android/widget/LinearLayout.java

/*
 * Copyright (C) 2006 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package android.widget;

import com.android.internal.R;

import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.graphics.drawable.Drawable;
import android.util.AttributeSet;
import android.view.Gravity;
import android.view.View;
import android.view.ViewDebug;
import android.view.ViewGroup;
import android.view.accessibility.AccessibilityEvent;
import android.view.accessibility.AccessibilityNodeInfo;
import android.widget.RemoteViews.RemoteView;


/**
 * A Layout that arranges its children in a single column or a single row. The direction of
 * the row can be set by calling {@link #setOrientation(int) setOrientation()}.
 * You can also specify gravity, which specifies the alignment of all the child elements by
 * calling {@link #setGravity(int) setGravity()} or specify that specific children
 * grow to fill up any remaining space in the layout by setting the <em>weight</em> member of
 * {@link android.widget.LinearLayout.LayoutParams LinearLayout.LayoutParams}.
 * The default orientation is horizontal.
 *
 * <p>See the <a href="{@docRoot}guide/topics/ui/layout/linear.html">Linear Layout</a>
 * guide.</p>
 *
 * <p>
 * Also see {@link LinearLayout.LayoutParams android.widget.LinearLayout.LayoutParams}
 * for layout attributes </p>
 *
 * @attr ref android.R.styleable#LinearLayout_baselineAligned
 * @attr ref android.R.styleable#LinearLayout_baselineAlignedChildIndex
 * @attr ref android.R.styleable#LinearLayout_gravity
 * @attr ref android.R.styleable#LinearLayout_measureWithLargestChild
 * @attr ref android.R.styleable#LinearLayout_orientation
 * @attr ref android.R.styleable#LinearLayout_weightSum
 */
@RemoteView
public class LinearLayout extends ViewGroup {
    public static final int HORIZONTAL = 0;
    public static final int VERTICAL = 1;

    /**
     * Don't show any dividers.
     */
    public static final int SHOW_DIVIDER_NONE = 0;
    /**
     * Show a divider at the beginning of the group.
     */
    public static final int SHOW_DIVIDER_BEGINNING = 1;
    /**
     * Show dividers between each item in the group.
     */
    public static final int SHOW_DIVIDER_MIDDLE = 2;
    /**
     * Show a divider at the end of the group.
     */
    public static final int SHOW_DIVIDER_END = 4;

    /**
     * Whether the children of this layout are baseline aligned.  Only applicable
     * if {@link #mOrientation} is horizontal.
     */
    @ViewDebug.ExportedProperty(category = "layout")
    private boolean mBaselineAligned = true;

    /**
     * If this layout is part of another layout that is baseline aligned,
     * use the child at this index as the baseline.
     *
     * Note: this is orthogonal to {@link #mBaselineAligned}, which is concerned
     * with whether the children of this layout are baseline aligned.
     */
    @ViewDebug.ExportedProperty(category = "layout")
    private int mBaselineAlignedChildIndex = -1;

    /**
     * The additional offset to the child's baseline.
     * We'll calculate the baseline of this layout as we measure vertically; for
     * horizontal linear layouts, the offset of 0 is appropriate.
     */
    @ViewDebug.ExportedProperty(category = "measurement")
    private int mBaselineChildTop = 0;

    @ViewDebug.ExportedProperty(category = "measurement")
    private int mOrientation;

    @ViewDebug.ExportedProperty(category = "measurement", flagMapping = {
            @ViewDebug.FlagToString(mask = -1,
                equals = -1, name = "NONE"),
            @ViewDebug.FlagToString(mask = Gravity.NO_GRAVITY,
                equals = Gravity.NO_GRAVITY,name = "NONE"),
            @ViewDebug.FlagToString(mask = Gravity.TOP,
                equals = Gravity.TOP, name = "TOP"),
            @ViewDebug.FlagToString(mask = Gravity.BOTTOM,
                equals = Gravity.BOTTOM, name = "BOTTOM"),
            @ViewDebug.FlagToString(mask = Gravity.LEFT,
                equals = Gravity.LEFT, name = "LEFT"),
            @ViewDebug.FlagToString(mask = Gravity.RIGHT,
                equals = Gravity.RIGHT, name = "RIGHT"),
            @ViewDebug.FlagToString(mask = Gravity.START,
                equals = Gravity.START, name = "START"),
            @ViewDebug.FlagToString(mask = Gravity.END,
                equals = Gravity.END, name = "END"),
            @ViewDebug.FlagToString(mask = Gravity.CENTER_VERTICAL,
                equals = Gravity.CENTER_VERTICAL, name = "CENTER_VERTICAL"),
            @ViewDebug.FlagToString(mask = Gravity.FILL_VERTICAL,
                equals = Gravity.FILL_VERTICAL, name = "FILL_VERTICAL"),
            @ViewDebug.FlagToString(mask = Gravity.CENTER_HORIZONTAL,
                equals = Gravity.CENTER_HORIZONTAL, name = "CENTER_HORIZONTAL"),
            @ViewDebug.FlagToString(mask = Gravity.FILL_HORIZONTAL,
                equals = Gravity.FILL_HORIZONTAL, name = "FILL_HORIZONTAL"),
            @ViewDebug.FlagToString(mask = Gravity.CENTER,
                equals = Gravity.CENTER, name = "CENTER"),
            @ViewDebug.FlagToString(mask = Gravity.FILL,
                equals = Gravity.FILL, name = "FILL"),
            @ViewDebug.FlagToString(mask = Gravity.RELATIVE_LAYOUT_DIRECTION,
                equals = Gravity.RELATIVE_LAYOUT_DIRECTION, name = "RELATIVE")
        })
    private int mGravity = Gravity.START | Gravity.TOP;

    @ViewDebug.ExportedProperty(category = "measurement")
    private int mTotalLength;

    @ViewDebug.ExportedProperty(category = "layout")
    private float mWeightSum;

    @ViewDebug.ExportedProperty(category = "layout")
    private boolean mUseLargestChild;

    private int[] mMaxAscent;
    private int[] mMaxDescent;

    private static final int VERTICAL_GRAVITY_COUNT = 4;

    private static final int INDEX_CENTER_VERTICAL = 0;
    private static final int INDEX_TOP = 1;
    private static final int INDEX_BOTTOM = 2;
    private static final int INDEX_FILL = 3;

    private Drawable mDivider;
    private int mDividerWidth;
    private int mDividerHeight;
    private int mShowDividers;
    private int mDividerPadding;

    public LinearLayout(Context context) {
        super(context);
    }

    public LinearLayout(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public LinearLayout(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);

        TypedArray a = context.obtainStyledAttributes(attrs,
                com.android.internal.R.styleable.LinearLayout, defStyle, 0);

        int index = a.getInt(com.android.internal.R.styleable.LinearLayout_orientation, -1);
        if (index >= 0) {
            setOrientation(index);
        }

        index = a.getInt(com.android.internal.R.styleable.LinearLayout_gravity, -1);
        if (index >= 0) {
            setGravity(index);
        }

        boolean baselineAligned = a.getBoolean(R.styleable.LinearLayout_baselineAligned, true);
        if (!baselineAligned) {
            setBaselineAligned(baselineAligned);
        }

        mWeightSum = a.getFloat(R.styleable.LinearLayout_weightSum, -1.0f);

        mBaselineAlignedChildIndex =
                a.getInt(com.android.internal.R.styleable.LinearLayout_baselineAlignedChildIndex, -1);

        mUseLargestChild = a.getBoolean(R.styleable.LinearLayout_measureWithLargestChild, false);

        setDividerDrawable(a.getDrawable(R.styleable.LinearLayout_divider));
        mShowDividers = a.getInt(R.styleable.LinearLayout_showDividers, SHOW_DIVIDER_NONE);
        mDividerPadding = a.getDimensionPixelSize(R.styleable.LinearLayout_dividerPadding, 0);

        a.recycle();
    }

    /**
     * Set how dividers should be shown between items in this layout
     *
     * @param showDividers One or more of {@link #SHOW_DIVIDER_BEGINNING},
     *                     {@link #SHOW_DIVIDER_MIDDLE}, or {@link #SHOW_DIVIDER_END},
     *                     or {@link #SHOW_DIVIDER_NONE} to show no dividers.
     */
    public void setShowDividers(int showDividers) {
        if (showDividers != mShowDividers) {
            requestLayout();
        }
        mShowDividers = showDividers;
    }

    @Override
    public boolean shouldDelayChildPressedState() {
        return false;
    }

    /**
     * @return A flag set indicating how dividers should be shown around items.
     * @see #setShowDividers(int)
     */
    public int getShowDividers() {
        return mShowDividers;
    }

    /**
     * @return the divider Drawable that will divide each item.
     *
     * @see #setDividerDrawable(Drawable)
     *
     * @attr ref android.R.styleable#LinearLayout_divider
     */
    public Drawable getDividerDrawable() {
        return mDivider;
    }

    /**
     * Set a drawable to be used as a divider between items.
     *
     * @param divider Drawable that will divide each item.
     *
     * @see #setShowDividers(int)
     *
     * @attr ref android.R.styleable#LinearLayout_divider
     */
    public void setDividerDrawable(Drawable divider) {
        if (divider == mDivider) {
            return;
        }
        mDivider = divider;
        if (divider != null) {
            mDividerWidth = divider.getIntrinsicWidth();
            mDividerHeight = divider.getIntrinsicHeight();
        } else {
            mDividerWidth = 0;
            mDividerHeight = 0;
        }
        setWillNotDraw(divider == null);
        requestLayout();
    }

    /**
     * Set padding displayed on both ends of dividers.
     *
     * @param padding Padding value in pixels that will be applied to each end
     *
     * @see #setShowDividers(int)
     * @see #setDividerDrawable(Drawable)
     * @see #getDividerPadding()
     */
    public void setDividerPadding(int padding) {
        mDividerPadding = padding;
    }

    /**
     * Get the padding size used to inset dividers in pixels
     *
     * @see #setShowDividers(int)
     * @see #setDividerDrawable(Drawable)
     * @see #setDividerPadding(int)
     */
    public int getDividerPadding() {
        return mDividerPadding;
    }

    /**
     * Get the width of the current divider drawable.
     *
     * @hide Used internally by framework.
     */
    public int getDividerWidth() {
        return mDividerWidth;
    }

    @Override
    protected void onDraw(Canvas canvas) {
        if (mDivider == null) {
            return;
        }

        if (mOrientation == VERTICAL) {
            drawDividersVertical(canvas);
        } else {
            drawDividersHorizontal(canvas);
        }
    }

    void drawDividersVertical(Canvas canvas) {
        final int count = getVirtualChildCount();
        for (int i = 0; i < count; i++) {
            final View child = getVirtualChildAt(i);

            if (child != null && child.getVisibility() != GONE) {
                if (hasDividerBeforeChildAt(i)) {
                    final LayoutParams lp = (LayoutParams) child.getLayoutParams();
                    final int top = child.getTop() - lp.topMargin - mDividerHeight;
                    drawHorizontalDivider(canvas, top);
                }
            }
        }

        if (hasDividerBeforeChildAt(count)) {
            final View child = getVirtualChildAt(count - 1);
            int bottom = 0;
            if (child == null) {
                bottom = getHeight() - getPaddingBottom() - mDividerHeight;
            } else {
                final LayoutParams lp = (LayoutParams) child.getLayoutParams();
                bottom = child.getBottom() + lp.bottomMargin;
            }
            drawHorizontalDivider(canvas, bottom);
        }
    }

    void drawDividersHorizontal(Canvas canvas) {
        final int count = getVirtualChildCount();
        final boolean isLayoutRtl = isLayoutRtl();
        for (int i = 0; i < count; i++) {
            final View child = getVirtualChildAt(i);

            if (child != null && child.getVisibility() != GONE) {
                if (hasDividerBeforeChildAt(i)) {
                    final LayoutParams lp = (LayoutParams) child.getLayoutParams();
                    final int position;
                    if (isLayoutRtl) {
                        position = child.getRight() + lp.rightMargin;
                    } else {
                        position = child.getLeft() - lp.leftMargin - mDividerWidth;
                    }
                    drawVerticalDivider(canvas, position);
                }
            }
        }

        if (hasDividerBeforeChildAt(count)) {
            final View child = getVirtualChildAt(count - 1);
            int position;
            if (child == null) {
                if (isLayoutRtl) {
                    position = getPaddingLeft();
                } else {
                    position = getWidth() - getPaddingRight() - mDividerWidth;
                }
            } else {
                final LayoutParams lp = (LayoutParams) child.getLayoutParams();
                if (isLayoutRtl) {
                    position = child.getLeft() - lp.leftMargin - mDividerWidth;
                } else {
                    position = child.getRight() + lp.rightMargin;
                }
            }
            drawVerticalDivider(canvas, position);
        }
    }

    void drawHorizontalDivider(Canvas canvas, int top) {
        mDivider.setBounds(getPaddingLeft() + mDividerPadding, top,
                getWidth() - getPaddingRight() - mDividerPadding, top + mDividerHeight);
        mDivider.draw(canvas);
    }

    void drawVerticalDivider(Canvas canvas, int left) {
        mDivider.setBounds(left, getPaddingTop() + mDividerPadding,
                left + mDividerWidth, getHeight() - getPaddingBottom() - mDividerPadding);
        mDivider.draw(canvas);
    }

    /**
     * <p>Indicates whether widgets contained within this layout are aligned
     * on their baseline or not.</p>
     *
     * @return true when widgets are baseline-aligned, false otherwise
     */
    public boolean isBaselineAligned() {
        return mBaselineAligned;
    }

    /**
     * <p>Defines whether widgets contained in this layout are
     * baseline-aligned or not.</p>
     *
     * @param baselineAligned true to align widgets on their baseline,
     *         false otherwise
     *
     * @attr ref android.R.styleable#LinearLayout_baselineAligned
     */
    @android.view.RemotableViewMethod
    public void setBaselineAligned(boolean baselineAligned) {
        mBaselineAligned = baselineAligned;
    }

    /**
     * When true, all children with a weight will be considered having
     * the minimum size of the largest child. If false, all children are
     * measured normally.
     *
     * @return True to measure children with a weight using the minimum
     *         size of the largest child, false otherwise.
     *
     * @attr ref android.R.styleable#LinearLayout_measureWithLargestChild
     */
    public boolean isMeasureWithLargestChildEnabled() {
        return mUseLargestChild;
    }

    /**
     * When set to true, all children with a weight will be considered having
     * the minimum size of the largest child. If false, all children are
     * measured normally.
     *
     * Disabled by default.
     *
     * @param enabled True to measure children with a weight using the
     *        minimum size of the largest child, false otherwise.
     *
     * @attr ref android.R.styleable#LinearLayout_measureWithLargestChild
     */
    @android.view.RemotableViewMethod
    public void setMeasureWithLargestChildEnabled(boolean enabled) {
        mUseLargestChild = enabled;
    }

    @Override
    public int getBaseline() {
        if (mBaselineAlignedChildIndex < 0) {
            return super.getBaseline();
        }

        if (getChildCount() <= mBaselineAlignedChildIndex) {
            throw new RuntimeException("mBaselineAlignedChildIndex of LinearLayout "
                    + "set to an index that is out of bounds.");
        }

        final View child = getChildAt(mBaselineAlignedChildIndex);
        final int childBaseline = child.getBaseline();

        if (childBaseline == -1) {
            if (mBaselineAlignedChildIndex == 0) {
                // this is just the default case, safe to return -1
                return -1;
            }
            // the user picked an index that points to something that doesn't
            // know how to calculate its baseline.
            throw new RuntimeException("mBaselineAlignedChildIndex of LinearLayout "
                    + "points to a View that doesn't know how to get its baseline.");
        }

        // TODO: This should try to take into account the virtual offsets
        // (See getNextLocationOffset and getLocationOffset)
        // We should add to childTop:
        // sum([getNextLocationOffset(getChildAt(i)) / i < mBaselineAlignedChildIndex])
        // and also add:
        // getLocationOffset(child)
        int childTop = mBaselineChildTop;

        if (mOrientation == VERTICAL) {
            final int majorGravity = mGravity & Gravity.VERTICAL_GRAVITY_MASK;
            if (majorGravity != Gravity.TOP) {
               switch (majorGravity) {
                   case Gravity.BOTTOM:
                       childTop = mBottom - mTop - mPaddingBottom - mTotalLength;
                       break;

                   case Gravity.CENTER_VERTICAL:
                       childTop += ((mBottom - mTop - mPaddingTop - mPaddingBottom) -
                               mTotalLength) / 2;
                       break;
               }
            }
        }

        LinearLayout.LayoutParams lp = (LinearLayout.LayoutParams) child.getLayoutParams();
        return childTop + lp.topMargin + childBaseline;
    }

    /**
     * @return The index of the child that will be used if this layout is
     *   part of a larger layout that is baseline aligned, or -1 if none has
     *   been set.
     */
    public int getBaselineAlignedChildIndex() {
        return mBaselineAlignedChildIndex;
    }

    /**
     * @param i The index of the child that will be used if this layout is
     *          part of a larger layout that is baseline aligned.
     *
     * @attr ref android.R.styleable#LinearLayout_baselineAlignedChildIndex
     */
    @android.view.RemotableViewMethod
    public void setBaselineAlignedChildIndex(int i) {
        if ((i < 0) || (i >= getChildCount())) {
            throw new IllegalArgumentException("base aligned child index out "
                    + "of range (0, " + getChildCount() + ")");
        }
        mBaselineAlignedChildIndex = i;
    }

    /**
     * <p>Returns the view at the specified index. This method can be overriden
     * to take into account virtual children. Refer to
     * {@link android.widget.TableLayout} and {@link android.widget.TableRow}
     * for an example.</p>
     *
     * @param index the child's index
     * @return the child at the specified index
     */
    View getVirtualChildAt(int index) {
        return getChildAt(index);
    }

    /**
     * <p>Returns the virtual number of children. This number might be different
     * than the actual number of children if the layout can hold virtual
     * children. Refer to
     * {@link android.widget.TableLayout} and {@link android.widget.TableRow}
     * for an example.</p>
     *
     * @return the virtual number of children
     */
    int getVirtualChildCount() {
        return getChildCount();
    }

    /**
     * Returns the desired weights sum.
     *
     * @return A number greater than 0.0f if the weight sum is defined, or
     *         a number lower than or equals to 0.0f if not weight sum is
     *         to be used.
     */
    public float getWeightSum() {
        return mWeightSum;
    }

    /**
     * Defines the desired weights sum. If unspecified the weights sum is computed
     * at layout time by adding the layout_weight of each child.
     *
     * This can be used for instance to give a single child 50% of the total
     * available space by giving it a layout_weight of 0.5 and setting the
     * weightSum to 1.0.
     *
     * @param weightSum a number greater than 0.0f, or a number lower than or equals
     *        to 0.0f if the weight sum should be computed from the children's
     *        layout_weight
     */
    @android.view.RemotableViewMethod
    public void setWeightSum(float weightSum) {
        mWeightSum = Math.max(0.0f, weightSum);
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        if (mOrientation == VERTICAL) {
            measureVertical(widthMeasureSpec, heightMeasureSpec);
        } else {
            measureHorizontal(widthMeasureSpec, heightMeasureSpec);
        }
    }

    /**
     * Determines where to position dividers between children.
     *
     * @param childIndex Index of child to check for preceding divider
     * @return true if there should be a divider before the child at childIndex
     * @hide Pending API consideration. Currently only used internally by the system.
     */
    protected boolean hasDividerBeforeChildAt(int childIndex) {
        if (childIndex == 0) {
            return (mShowDividers & SHOW_DIVIDER_BEGINNING) != 0;
        } else if (childIndex == getChildCount()) {
            return (mShowDividers & SHOW_DIVIDER_END) != 0;
        } else if ((mShowDividers & SHOW_DIVIDER_MIDDLE) != 0) {
            boolean hasVisibleViewBefore = false;
            for (int i = childIndex - 1; i >= 0; i--) {
                if (getChildAt(i).getVisibility() != GONE) {
                    hasVisibleViewBefore = true;
                    break;
                }
            }
            return hasVisibleViewBefore;
        }
        return false;
    }

    /**
     * Measures the children when the orientation of this LinearLayout is set
     * to {@link #VERTICAL}.
     *
     * @param widthMeasureSpec Horizontal space requirements as imposed by the parent.
     * @param heightMeasureSpec Vertical space requirements as imposed by the parent.
     *
     * @see #getOrientation()
     * @see #setOrientation(int)
     * @see #onMeasure(int, int)
     */
    void measureVertical(int widthMeasureSpec, int heightMeasureSpec) {
        mTotalLength = 0;
        int maxWidth = 0;
        int childState = 0;
        int alternativeMaxWidth = 0;
        int weightedMaxWidth = 0;
        boolean allFillParent = true;
        float totalWeight = 0;

        final int count = getVirtualChildCount();

        final int widthMode = MeasureSpec.getMode(widthMeasureSpec);
        final int heightMode = MeasureSpec.getMode(heightMeasureSpec);

        boolean matchWidth = false;

        final int baselineChildIndex = mBaselineAlignedChildIndex;
        final boolean useLargestChild = mUseLargestChild;

        int largestChildHeight = Integer.MIN_VALUE;

        // See how tall everyone is. Also remember max width.
        for (int i = 0; i < count; ++i) {
            final View child = getVirtualChildAt(i);

            if (child == null) {
                mTotalLength += measureNullChild(i);
                continue;
            }

            if (child.getVisibility() == View.GONE) {
               i += getChildrenSkipCount(child, i);
               continue;
            }

            if (hasDividerBeforeChildAt(i)) {
                mTotalLength += mDividerHeight;
            }

            LinearLayout.LayoutParams lp = (LinearLayout.LayoutParams) child.getLayoutParams();

            totalWeight += lp.weight;

            if (heightMode == MeasureSpec.EXACTLY && lp.height == 0 && lp.weight > 0) {
                // Optimization: don't bother measuring children who are going to use
                // leftover space. These views will get measured again down below if
                // there is any leftover space.
                final int totalLength = mTotalLength;
                mTotalLength = Math.max(totalLength, totalLength + lp.topMargin + lp.bottomMargin);
            } else {
                int oldHeight = Integer.MIN_VALUE;

                if (lp.height == 0 && lp.weight > 0) {
                    // heightMode is either UNSPECIFIED or AT_MOST, and this
                    // child wanted to stretch to fill available space.
                    // Translate that to WRAP_CONTENT so that it does not end up
                    // with a height of 0
                    oldHeight = 0;
                    lp.height = LayoutParams.WRAP_CONTENT;
                }

                // Determine how big this child would like to be. If this or
                // previous children have given a weight, then we allow it to
                // use all available space (and we will shrink things later
                // if needed).
                measureChildBeforeLayout(
                       child, i, widthMeasureSpec, 0, heightMeasureSpec,
                       totalWeight == 0 ? mTotalLength : 0);

                if (oldHeight != Integer.MIN_VALUE) {
                   lp.height = oldHeight;
                }

                final int childHeight = child.getMeasuredHeight();
                final int totalLength = mTotalLength;
                mTotalLength = Math.max(totalLength, totalLength + childHeight + lp.topMargin +
                       lp.bottomMargin + getNextLocationOffset(child));

                if (useLargestChild) {
                    largestChildHeight = Math.max(childHeight, largestChildHeight);
                }
            }

            /**
             * If applicable, compute the additional offset to the child's baseline
             * we'll need later when asked {@link #getBaseline}.
             */
            if ((baselineChildIndex >= 0) && (baselineChildIndex == i + 1)) {
               mBaselineChildTop = mTotalLength;
            }

            // if we are trying to use a child index for our baseline, the above
            // book keeping only works if there are no children above it with
            // weight.  fail fast to aid the developer.
            if (i < baselineChildIndex && lp.weight > 0) {
                throw new RuntimeException("A child of LinearLayout with index "
                        + "less than mBaselineAlignedChildIndex has weight > 0, which "
                        + "won't work.  Either remove the weight, or don't set "
                        + "mBaselineAlignedChildIndex.");
            }

            boolean matchWidthLocally = false;
            if (widthMode != MeasureSpec.EXACTLY && lp.width == LayoutParams.MATCH_PARENT) {
                // The width of the linear layout will scale, and at least one
                // child said it wanted to match our width. Set a flag
                // indicating that we need to remeasure at least that view when
                // we know our width.
                matchWidth = true;
                matchWidthLocally = true;
            }

            final int margin = lp.leftMargin + lp.rightMargin;
            final int measuredWidth = child.getMeasuredWidth() + margin;
            maxWidth = Math.max(maxWidth, measuredWidth);
            childState = combineMeasuredStates(childState, child.getMeasuredState());

            allFillParent = allFillParent && lp.width == LayoutParams.MATCH_PARENT;
            if (lp.weight > 0) {
                /*
                 * Widths of weighted Views are bogus if we end up
                 * remeasuring, so keep them separate.
                 */
                weightedMaxWidth = Math.max(weightedMaxWidth,
                        matchWidthLocally ? margin : measuredWidth);
            } else {
                alternativeMaxWidth = Math.max(alternativeMaxWidth,
                        matchWidthLocally ? margin : measuredWidth);
            }

            i += getChildrenSkipCount(child, i);
        }

        if (mTotalLength > 0 && hasDividerBeforeChildAt(count)) {
            mTotalLength += mDividerHeight;
        }

        if (useLargestChild &&
                (heightMode == MeasureSpec.AT_MOST || heightMode == MeasureSpec.UNSPECIFIED)) {
            mTotalLength = 0;

            for (int i = 0; i < count; ++i) {
                final View child = getVirtualChildAt(i);

                if (child == null) {
                    mTotalLength += measureNullChild(i);
                    continue;
                }

                if (child.getVisibility() == GONE) {
                    i += getChildrenSkipCount(child, i);
                    continue;
                }

                final LinearLayout.LayoutParams lp = (LinearLayout.LayoutParams)
                        child.getLayoutParams();
                // Account for negative margins
                final int totalLength = mTotalLength;
                mTotalLength = Math.max(totalLength, totalLength + largestChildHeight +
                        lp.topMargin + lp.bottomMargin + getNextLocationOffset(child));
            }
        }

        // Add in our padding
        mTotalLength += mPaddingTop + mPaddingBottom;

        int heightSize = mTotalLength;

        // Check against our minimum height
        heightSize = Math.max(heightSize, getSuggestedMinimumHeight());

        // Reconcile our calculated size with the heightMeasureSpec
        int heightSizeAndState = resolveSizeAndState(heightSize, heightMeasureSpec, 0);
        heightSize = heightSizeAndState & MEASURED_SIZE_MASK;

        // Either expand children with weight to take up available space or
        // shrink them if they extend beyond our current bounds
        int delta = heightSize - mTotalLength;
        if (delta != 0 && totalWeight > 0.0f) {
            float weightSum = mWeightSum > 0.0f ? mWeightSum : totalWeight;

            mTotalLength = 0;

            for (int i = 0; i < count; ++i) {
                final View child = getVirtualChildAt(i);

                if (child.getVisibility() == View.GONE) {
                    continue;
                }

                LinearLayout.LayoutParams lp = (LinearLayout.LayoutParams) child.getLayoutParams();

                float childExtra = lp.weight;
                if (childExtra > 0) {
                    // Child said it could absorb extra space -- give him his share
                    int share = (int) (childExtra * delta / weightSum);
                    weightSum -= childExtra;
                    delta -= share;

                    final int childWidthMeasureSpec = getChildMeasureSpec(widthMeasureSpec,
                            mPaddingLeft + mPaddingRight +
                                    lp.leftMargin + lp.rightMargin, lp.width);

                    // TODO: Use a field like lp.isMeasured to figure out if this
                    // child has been previously measured
                    if ((lp.height != 0) || (heightMode != MeasureSpec.EXACTLY)) {
                        // child was measured once already above...
                        // base new measurement on stored values
                        int childHeight = child.getMeasuredHeight() + share;
                        if (childHeight < 0) {
                            childHeight = 0;
                        }

                        child.measure(childWidthMeasureSpec,
                                MeasureSpec.makeMeasureSpec(childHeight, MeasureSpec.EXACTLY));
                    } else {
                        // child was skipped in the loop above.
                        // Measure for this first time here
                        child.measure(childWidthMeasureSpec,
                                MeasureSpec.makeMeasureSpec(share > 0 ? share : 0,
                                        MeasureSpec.EXACTLY));
                    }

                    // Child may now not fit in vertical dimension.
                    childState = combineMeasuredStates(childState, child.getMeasuredState()
                            & (MEASURED_STATE_MASK>>MEASURED_HEIGHT_STATE_SHIFT));
                }

                final int margin =  lp.leftMargin + lp.rightMargin;
                final int measuredWidth = child.getMeasuredWidth() + margin;
                maxWidth = Math.max(maxWidth, measuredWidth);

                boolean matchWidthLocally = widthMode != MeasureSpec.EXACTLY &&
                        lp.width == LayoutParams.MATCH_PARENT;

                alternativeMaxWidth = Math.max(alternativeMaxWidth,
                        matchWidthLocally ? margin : measuredWidth);

                allFillParent = allFillParent && lp.width == LayoutParams.MATCH_PARENT;

                final int totalLength = mTotalLength;
                mTotalLength = Math.max(totalLength, totalLength + child.getMeasuredHeight() +
                        lp.topMargin + lp.bottomMargin + getNextLocationOffset(child));
            }

            // Add in our padding
            mTotalLength += mPaddingTop + mPaddingBottom;
            // TODO: Should we recompute the heightSpec based on the new total length?
        } else {
            alternativeMaxWidth = Math.max(alternativeMaxWidth,
                                           weightedMaxWidth);


            // We have no limit, so make all weighted views as tall as the largest child.
            // Children will have already been measured once.
            if (useLargestChild && heightMode != MeasureSpec.EXACTLY) {
                for (int i = 0; i < count; i++) {
                    final View child = getVirtualChildAt(i);

                    if (child == null || child.getVisibility() == View.GONE) {
                        continue;
                    }

                    final LinearLayout.LayoutParams lp =
                            (LinearLayout.LayoutParams) child.getLayoutParams();

                    float childExtra = lp.weight;
                    if (childExtra > 0) {
                        child.measure(
                                MeasureSpec.makeMeasureSpec(child.getMeasuredWidth(),
                                        MeasureSpec.EXACTLY),
                                MeasureSpec.makeMeasureSpec(largestChildHeight,
                                        MeasureSpec.EXACTLY));
                    }
                }
            }
        }

        if (!allFillParent && widthMode != MeasureSpec.EXACTLY) {
            maxWidth = alternativeMaxWidth;
        }

        maxWidth += mPaddingLeft + mPaddingRight;

        // Check against our minimum width
        maxWidth = Math.max(maxWidth, getSuggestedMinimumWidth());

        setMeasuredDimension(resolveSizeAndState(maxWidth, widthMeasureSpec, childState),
                heightSizeAndState);

        if (matchWidth) {
            forceUniformWidth(count, heightMeasureSpec);
        }
    }

    private void forceUniformWidth(int count, int heightMeasureSpec) {
        // Pretend that the linear layout has an exact size.
        int uniformMeasureSpec = MeasureSpec.makeMeasureSpec(getMeasuredWidth(),
                MeasureSpec.EXACTLY);
        for (int i = 0; i< count; ++i) {
           final View child = getVirtualChildAt(i);
           if (child.getVisibility() != GONE) {
               LinearLayout.LayoutParams lp = ((LinearLayout.LayoutParams)child.getLayoutParams());

               if (lp.width == LayoutParams.MATCH_PARENT) {
                   // Temporarily force children to reuse their old measured height
                   // FIXME: this may not be right for something like wrapping text?
                   int oldHeight = lp.height;
                   lp.height = child.getMeasuredHeight();

                   // Remeasue with new dimensions
                   measureChildWithMargins(child, uniformMeasureSpec, 0, heightMeasureSpec, 0);
                   lp.height = oldHeight;
               }
           }
        }
    }

    /**
     * Measures the children when the orientation of this LinearLayout is set
     * to {@link #HORIZONTAL}.
     *
     * @param widthMeasureSpec Horizontal space requirements as imposed by the parent.
     * @param heightMeasureSpec Vertical space requirements as imposed by the parent.
     *
     * @see #getOrientation()
     * @see #setOrientation(int)
     * @see #onMeasure(int, int)
     */
    void measureHorizontal(int widthMeasureSpec, int heightMeasureSpec) {
        mTotalLength = 0;
        int maxHeight = 0;
        int childState = 0;
        int alternativeMaxHeight = 0;
        int weightedMaxHeight = 0;
        boolean allFillParent = true;
        float totalWeight = 0;

        final int count = getVirtualChildCount();

        final int widthMode = MeasureSpec.getMode(widthMeasureSpec);
        final int heightMode = MeasureSpec.getMode(heightMeasureSpec);

        boolean matchHeight = false;

        if (mMaxAscent == null || mMaxDescent == null) {
            mMaxAscent = new int[VERTICAL_GRAVITY_COUNT];
            mMaxDescent = new int[VERTICAL_GRAVITY_COUNT];
        }

        final int[] maxAscent = mMaxAscent;
        final int[] maxDescent = mMaxDescent;

        maxAscent[0] = maxAscent[1] = maxAscent[2] = maxAscent[3] = -1;
        maxDescent[0] = maxDescent[1] = maxDescent[2] = maxDescent[3] = -1;

        final boolean baselineAligned = mBaselineAligned;
        final boolean useLargestChild = mUseLargestChild;

        final boolean isExactly = widthMode == MeasureSpec.EXACTLY;

        int largestChildWidth = Integer.MIN_VALUE;

        // See how wide everyone is. Also remember max height.
        for (int i = 0; i < count; ++i) {
            final View child = getVirtualChildAt(i);

            if (child == null) {
                mTotalLength += measureNullChild(i);
                continue;
            }

            if (child.getVisibility() == GONE) {
                i += getChildrenSkipCount(child, i);
                continue;
            }

            if (hasDividerBeforeChildAt(i)) {
                mTotalLength += mDividerWidth;
            }

            final LinearLayout.LayoutParams lp = (LinearLayout.LayoutParams)
                    child.getLayoutParams();

            totalWeight += lp.weight;

            if (widthMode == MeasureSpec.EXACTLY && lp.width == 0 && lp.weight > 0) {
                // Optimization: don't bother measuring children who are going to use
                // leftover space. These views will get measured again down below if
                // there is any leftover space.
                if (isExactly) {
                    mTotalLength += lp.leftMargin + lp.rightMargin;
                } else {
                    final int totalLength = mTotalLength;
                    mTotalLength = Math.max(totalLength, totalLength +
                            lp.leftMargin + lp.rightMargin);
                }

                // Baseline alignment requires to measure widgets to obtain the
                // baseline offset (in particular for TextViews). The following
                // defeats the optimization mentioned above. Allow the child to
                // use as much space as it wants because we can shrink things
                // later (and re-measure).
                if (baselineAligned) {
                    final int freeSpec = MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED);
                    child.measure(freeSpec, freeSpec);
                }
            } else {
                int oldWidth = Integer.MIN_VALUE;

                if (lp.width == 0 && lp.weight > 0) {
                    // widthMode is either UNSPECIFIED or AT_MOST, and this
                    // child
                    // wanted to stretch to fill available space. Translate that to
                    // WRAP_CONTENT so that it does not end up with a width of 0
                    oldWidth = 0;
                    lp.width = LayoutParams.WRAP_CONTENT;
                }

                // Determine how big this child would like to be. If this or
                // previous children have given a weight, then we allow it to
                // use all available space (and we will shrink things later
                // if needed).
                measureChildBeforeLayout(child, i, widthMeasureSpec,
                        totalWeight == 0 ? mTotalLength : 0,
                        heightMeasureSpec, 0);

                if (oldWidth != Integer.MIN_VALUE) {
                    lp.width = oldWidth;
                }

                final int childWidth = child.getMeasuredWidth();
                if (isExactly) {
                    mTotalLength += childWidth + lp.leftMargin + lp.rightMargin +
                            getNextLocationOffset(child);
                } else {
                    final int totalLength = mTotalLength;
                    mTotalLength = Math.max(totalLength, totalLength + childWidth + lp.leftMargin +
                           lp.rightMargin + getNextLocationOffset(child));
                }

                if (useLargestChild) {
                    largestChildWidth = Math.max(childWidth, largestChildWidth);
                }
            }

            boolean matchHeightLocally = false;
            if (heightMode != MeasureSpec.EXACTLY && lp.height == LayoutParams.MATCH_PARENT) {
                // The height of the linear layout will scale, and at least one
                // child said it wanted to match our height. Set a flag indicating that
                // we need to remeasure at least that view when we know our height.
                matchHeight = true;
                matchHeightLocally = true;
            }

            final int margin = lp.topMargin + lp.bottomMargin;
            final int childHeight = child.getMeasuredHeight() + margin;
            childState = combineMeasuredStates(childState, child.getMeasuredState());

            if (baselineAligned) {
                final int childBaseline = child.getBaseline();
                if (childBaseline != -1) {
                    // Translates the child's vertical gravity into an index
                    // in the range 0..VERTICAL_GRAVITY_COUNT
                    final int gravity = (lp.gravity < 0 ? mGravity : lp.gravity)
                            & Gravity.VERTICAL_GRAVITY_MASK;
                    final int index = ((gravity >> Gravity.AXIS_Y_SHIFT)
                            & ~Gravity.AXIS_SPECIFIED) >> 1;

                    maxAscent[index] = Math.max(maxAscent[index], childBaseline);
                    maxDescent[index] = Math.max(maxDescent[index], childHeight - childBaseline);
                }
            }

            maxHeight = Math.max(maxHeight, childHeight);

            allFillParent = allFillParent && lp.height == LayoutParams.MATCH_PARENT;
            if (lp.weight > 0) {
                /*
                 * Heights of weighted Views are bogus if we end up
                 * remeasuring, so keep them separate.
                 */
                weightedMaxHeight = Math.max(weightedMaxHeight,
                        matchHeightLocally ? margin : childHeight);
            } else {
                alternativeMaxHeight = Math.max(alternativeMaxHeight,
                        matchHeightLocally ? margin : childHeight);
            }

            i += getChildrenSkipCount(child, i);
        }

        if (mTotalLength > 0 && hasDividerBeforeChildAt(count)) {
            mTotalLength += mDividerWidth;
        }

        // Check mMaxAscent[INDEX_TOP] first because it maps to Gravity.TOP,
        // the most common case
        if (maxAscent[INDEX_TOP] != -1 ||
                maxAscent[INDEX_CENTER_VERTICAL] != -1 ||
                maxAscent[INDEX_BOTTOM] != -1 ||
                maxAscent[INDEX_FILL] != -1) {
            final int ascent = Math.max(maxAscent[INDEX_FILL],
                    Math.max(maxAscent[INDEX_CENTER_VERTICAL],
                    Math.max(maxAscent[INDEX_TOP], maxAscent[INDEX_BOTTOM])));
            final int descent = Math.max(maxDescent[INDEX_FILL],
                    Math.max(maxDescent[INDEX_CENTER_VERTICAL],
                    Math.max(maxDescent[INDEX_TOP], maxDescent[INDEX_BOTTOM])));
            maxHeight = Math.max(maxHeight, ascent + descent);
        }

        if (useLargestChild &&
                (widthMode == MeasureSpec.AT_MOST || widthMode == MeasureSpec.UNSPECIFIED)) {
            mTotalLength = 0;

            for (int i = 0; i < count; ++i) {
                final View child = getVirtualChildAt(i);

                if (child == null) {
                    mTotalLength += measureNullChild(i);
                    continue;
                }

                if (child.getVisibility() == GONE) {
                    i += getChildrenSkipCount(child, i);
                    continue;
                }

                final LinearLayout.LayoutParams lp = (LinearLayout.LayoutParams)
                        child.getLayoutParams();
                if (isExactly) {
                    mTotalLength += largestChildWidth + lp.leftMargin + lp.rightMargin +
                            getNextLocationOffset(child);
                } else {
                    final int totalLength = mTotalLength;
                    mTotalLength = Math.max(totalLength, totalLength + largestChildWidth +
                            lp.leftMargin + lp.rightMargin + getNextLocationOffset(child));
                }
            }
        }

        // Add in our padding
        mTotalLength += mPaddingLeft + mPaddingRight;

        int widthSize = mTotalLength;

        // Check against our minimum width
        widthSize = Math.max(widthSize, getSuggestedMinimumWidth());

        // Reconcile our calculated size with the widthMeasureSpec
        int widthSizeAndState = resolveSizeAndState(widthSize, widthMeasureSpec, 0);
        widthSize = widthSizeAndState & MEASURED_SIZE_MASK;

        // Either expand children with weight to take up available space or
        // shrink them if they extend beyond our current bounds
        int delta = widthSize - mTotalLength;
        if (delta != 0 && totalWeight > 0.0f) {
            float weightSum = mWeightSum > 0.0f ? mWeightSum : totalWeight;

            maxAscent[0] = maxAscent[1] = maxAscent[2] = maxAscent[3] = -1;
            maxDescent[0] = maxDescent[1] = maxDescent[2] = maxDescent[3] = -1;
            maxHeight = -1;

            mTotalLength = 0;

            for (int i = 0; i < count; ++i) {
                final View child = getVirtualChildAt(i);

                if (child == null || child.getVisibility() == View.GONE) {
                    continue;
                }

                final LinearLayout.LayoutParams lp =
                        (LinearLayout.LayoutParams) child.getLayoutParams();

                float childExtra = lp.weight;
                if (childExtra > 0) {
                    // Child said it could absorb extra space -- give him his share
                    int share = (int) (childExtra * delta / weightSum);
                    weightSum -= childExtra;
                    delta -= share;

                    final int childHeightMeasureSpec = getChildMeasureSpec(
                            heightMeasureSpec,
                            mPaddingTop + mPaddingBottom + lp.topMargin + lp.bottomMargin,
                            lp.height);

                    // TODO: Use a field like lp.isMeasured to figure out if this
                    // child has been previously measured
                    if ((lp.width != 0) || (widthMode != MeasureSpec.EXACTLY)) {
                        // child was measured once already above ... base new measurement
                        // on stored values
                        int childWidth = child.getMeasuredWidth() + share;
                        if (childWidth < 0) {
                            childWidth = 0;
                        }

                        child.measure(
                            MeasureSpec.makeMeasureSpec(childWidth, MeasureSpec.EXACTLY),
                            childHeightMeasureSpec);
                    } else {
                        // child was skipped in the loop above. Measure for this first time here
                        child.measure(MeasureSpec.makeMeasureSpec(
                                share > 0 ? share : 0, MeasureSpec.EXACTLY),
                                childHeightMeasureSpec);
                    }

                    // Child may now not fit in horizontal dimension.
                    childState = combineMeasuredStates(childState,
                            child.getMeasuredState() & MEASURED_STATE_MASK);
                }

                if (isExactly) {
                    mTotalLength += child.getMeasuredWidth() + lp.leftMargin + lp.rightMargin +
                            getNextLocationOffset(child);
                } else {
                    final int totalLength = mTotalLength;
                    mTotalLength = Math.max(totalLength, totalLength + child.getMeasuredWidth() +
                            lp.leftMargin + lp.rightMargin + getNextLocationOffset(child));
                }

                boolean matchHeightLocally = heightMode != MeasureSpec.EXACTLY &&
                        lp.height == LayoutParams.MATCH_PARENT;

                final int margin = lp.topMargin + lp .bottomMargin;
                int childHeight = child.getMeasuredHeight() + margin;
                maxHeight = Math.max(maxHeight, childHeight);
                alternativeMaxHeight = Math.max(alternativeMaxHeight,
                        matchHeightLocally ? margin : childHeight);

                allFillParent = allFillParent && lp.height == LayoutParams.MATCH_PARENT;

                if (baselineAligned) {
                    final int childBaseline = child.getBaseline();
                    if (childBaseline != -1) {
                        // Translates the child's vertical gravity into an index in the range 0..2
                        final int gravity = (lp.gravity < 0 ? mGravity : lp.gravity)
                                & Gravity.VERTICAL_GRAVITY_MASK;
                        final int index = ((gravity >> Gravity.AXIS_Y_SHIFT)
                                & ~Gravity.AXIS_SPECIFIED) >> 1;

                        maxAscent[index] = Math.max(maxAscent[index], childBaseline);
                        maxDescent[index] = Math.max(maxDescent[index],
                                childHeight - childBaseline);
                    }
                }
            }

            // Add in our padding
            mTotalLength += mPaddingLeft + mPaddingRight;
            // TODO: Should we update widthSize with the new total length?

            // Check mMaxAscent[INDEX_TOP] first because it maps to Gravity.TOP,
            // the most common case
            if (maxAscent[INDEX_TOP] != -1 ||
                    maxAscent[INDEX_CENTER_VERTICAL] != -1 ||
                    maxAscent[INDEX_BOTTOM] != -1 ||
                    maxAscent[INDEX_FILL] != -1) {
                final int ascent = Math.max(maxAscent[INDEX_FILL],
                        Math.max(maxAscent[INDEX_CENTER_VERTICAL],
                        Math.max(maxAscent[INDEX_TOP], maxAscent[INDEX_BOTTOM])));
                final int descent = Math.max(maxDescent[INDEX_FILL],
                        Math.max(maxDescent[INDEX_CENTER_VERTICAL],
                        Math.max(maxDescent[INDEX_TOP], maxDescent[INDEX_BOTTOM])));
                maxHeight = Math.max(maxHeight, ascent + descent);
            }
        } else {
            alternativeMaxHeight = Math.max(alternativeMaxHeight, weightedMaxHeight);

            // We have no limit, so make all weighted views as wide as the largest child.
            // Children will have already been measured once.
            if (useLargestChild && widthMode != MeasureSpec.EXACTLY) {
                for (int i = 0; i < count; i++) {
                    final View child = getVirtualChildAt(i);

                    if (child == null || child.getVisibility() == View.GONE) {
                        continue;
                    }

                    final LinearLayout.LayoutParams lp =
                            (LinearLayout.LayoutParams) child.getLayoutParams();

                    float childExtra = lp.weight;
                    if (childExtra > 0) {
                        child.measure(
                                MeasureSpec.makeMeasureSpec(largestChildWidth, MeasureSpec.EXACTLY),
                                MeasureSpec.makeMeasureSpec(child.getMeasuredHeight(),
                                        MeasureSpec.EXACTLY));
                    }
                }
            }
        }

        if (!allFillParent && heightMode != MeasureSpec.EXACTLY) {
            maxHeight = alternativeMaxHeight;
        }

        maxHeight += mPaddingTop + mPaddingBottom;

        // Check against our minimum height
        maxHeight = Math.max(maxHeight, getSuggestedMinimumHeight());

        setMeasuredDimension(widthSizeAndState | (childState&MEASURED_STATE_MASK),
                resolveSizeAndState(maxHeight, heightMeasureSpec,
                        (childState<<MEASURED_HEIGHT_STATE_SHIFT)));

        if (matchHeight) {
            forceUniformHeight(count, widthMeasureSpec);
        }
    }

    private void forceUniformHeight(int count, int widthMeasureSpec) {
        // Pretend that the linear layout has an exact size. This is the measured height of
        // ourselves. The measured height should be the max height of the children, changed
        // to accommodate the heightMeasureSpec from the parent
        int uniformMeasureSpec = MeasureSpec.makeMeasureSpec(getMeasuredHeight(),
                MeasureSpec.EXACTLY);
        for (int i = 0; i < count; ++i) {
           final View child = getVirtualChildAt(i);
           if (child.getVisibility() != GONE) {
               LinearLayout.LayoutParams lp = (LinearLayout.LayoutParams) child.getLayoutParams();

               if (lp.height == LayoutParams.MATCH_PARENT) {
                   // Temporarily force children to reuse their old measured width
                   // FIXME: this may not be right for something like wrapping text?
                   int oldWidth = lp.width;
                   lp.width = child.getMeasuredWidth();

                   // Remeasure with new dimensions
                   measureChildWithMargins(child, widthMeasureSpec, 0, uniformMeasureSpec, 0);
                   lp.width = oldWidth;
               }
           }
        }
    }

    /**
     * <p>Returns the number of children to skip after measuring/laying out
     * the specified child.</p>
     *
     * @param child the child after which we want to skip children
     * @param index the index of the child after which we want to skip children
     * @return the number of children to skip, 0 by default
     */
    int getChildrenSkipCount(View child, int index) {
        return 0;
    }

    /**
     * <p>Returns the size (width or height) that should be occupied by a null
     * child.</p>
     *
     * @param childIndex the index of the null child
     * @return the width or height of the child depending on the orientation
     */
    int measureNullChild(int childIndex) {
        return 0;
    }

    /**
     * <p>Measure the child according to the parent's measure specs. This
     * method should be overriden by subclasses to force the sizing of
     * children. This method is called by {@link #measureVertical(int, int)} and
     * {@link #measureHorizontal(int, int)}.</p>
     *
     * @param child the child to measure
     * @param childIndex the index of the child in this view
     * @param widthMeasureSpec horizontal space requirements as imposed by the parent
     * @param totalWidth extra space that has been used up by the parent horizontally
     * @param heightMeasureSpec vertical space requirements as imposed by the parent
     * @param totalHeight extra space that has been used up by the parent vertically
     */
    void measureChildBeforeLayout(View child, int childIndex,
            int widthMeasureSpec, int totalWidth, int heightMeasureSpec,
            int totalHeight) {
        measureChildWithMargins(child, widthMeasureSpec, totalWidth,
                heightMeasureSpec, totalHeight);
    }

    /**
     * <p>Return the location offset of the specified child. This can be used
     * by subclasses to change the location of a given widget.</p>
     *
     * @param child the child for which to obtain the location offset
     * @return the location offset in pixels
     */
    int getLocationOffset(View child) {
        return 0;
    }

    /**
     * <p>Return the size offset of the next sibling of the specified child.
     * This can be used by subclasses to change the location of the widget
     * following <code>child</code>.</p>
     *
     * @param child the child whose next sibling will be moved
     * @return the location offset of the next child in pixels
     */
    int getNextLocationOffset(View child) {
        return 0;
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        if (mOrientation == VERTICAL) {
            layoutVertical(l, t, r, b);
        } else {
            layoutHorizontal(l, t, r, b);
        }
    }

    /**
     * Position the children during a layout pass if the orientation of this
     * LinearLayout is set to {@link #VERTICAL}.
     *
     * @see #getOrientation()
     * @see #setOrientation(int)
     * @see #onLayout(boolean, int, int, int, int)
     * @param left
     * @param top
     * @param right
     * @param bottom
     */
    void layoutVertical(int left, int top, int right, int bottom) {
        final int paddingLeft = mPaddingLeft;

        int childTop;
        int childLeft;

        // Where right end of child should go
        final int width = right - left;
        int childRight = width - mPaddingRight;

        // Space available for child
        int childSpace = width - paddingLeft - mPaddingRight;

        final int count = getVirtualChildCount();

        final int majorGravity = mGravity & Gravity.VERTICAL_GRAVITY_MASK;
        final int minorGravity = mGravity & Gravity.RELATIVE_HORIZONTAL_GRAVITY_MASK;

        switch (majorGravity) {
           case Gravity.BOTTOM:
               // mTotalLength contains the padding already
               childTop = mPaddingTop + bottom - top - mTotalLength;
               break;

               // mTotalLength contains the padding already
           case Gravity.CENTER_VERTICAL:
               childTop = mPaddingTop + (bottom - top - mTotalLength) / 2;
               break;

           case Gravity.TOP:
           default:
               childTop = mPaddingTop;
               break;
        }

        for (int i = 0; i < count; i++) {
            final View child = getVirtualChildAt(i);
            if (child == null) {
                childTop += measureNullChild(i);
            } else if (child.getVisibility() != GONE) {
                final int childWidth = child.getMeasuredWidth();
                final int childHeight = child.getMeasuredHeight();

                final LinearLayout.LayoutParams lp =
                        (LinearLayout.LayoutParams) child.getLayoutParams();

                int gravity = lp.gravity;
                if (gravity < 0) {
                    gravity = minorGravity;
                }
                final int layoutDirection = getLayoutDirection();
                final int absoluteGravity = Gravity.getAbsoluteGravity(gravity, layoutDirection);
                switch (absoluteGravity & Gravity.HORIZONTAL_GRAVITY_MASK) {
                    case Gravity.CENTER_HORIZONTAL:
                        childLeft = paddingLeft + ((childSpace - childWidth) / 2)
                                + lp.leftMargin - lp.rightMargin;
                        break;

                    case Gravity.RIGHT:
                        childLeft = childRight - childWidth - lp.rightMargin;
                        break;

                    case Gravity.LEFT:
                    default:
                        childLeft = paddingLeft + lp.leftMargin;
                        break;
                }

                if (hasDividerBeforeChildAt(i)) {
                    childTop += mDividerHeight;
                }

                childTop += lp.topMargin;
                setChildFrame(child, childLeft, childTop + getLocationOffset(child),
                        childWidth, childHeight);
                childTop += childHeight + lp.bottomMargin + getNextLocationOffset(child);

                i += getChildrenSkipCount(child, i);
            }
        }
    }

    /**
     * Position the children during a layout pass if the orientation of this
     * LinearLayout is set to {@link #HORIZONTAL}.
     *
     * @see #getOrientation()
     * @see #setOrientation(int)
     * @see #onLayout(boolean, int, int, int, int)
     * @param left
     * @param top
     * @param right
     * @param bottom
     */
    void layoutHorizontal(int left, int top, int right, int bottom) {
        final boolean isLayoutRtl = isLayoutRtl();
        final int paddingTop = mPaddingTop;

        int childTop;
        int childLeft;

        // Where bottom of child should go
        final int height = bottom - top;
        int childBottom = height - mPaddingBottom;

        // Space available for child
        int childSpace = height - paddingTop - mPaddingBottom;

        final int count = getVirtualChildCount();

        final int majorGravity = mGravity & Gravity.RELATIVE_HORIZONTAL_GRAVITY_MASK;
        final int minorGravity = mGravity & Gravity.VERTICAL_GRAVITY_MASK;

        final boolean baselineAligned = mBaselineAligned;

        final int[] maxAscent = mMaxAscent;
        final int[] maxDescent = mMaxDescent;

        final int layoutDirection = getLayoutDirection();
        switch (Gravity.getAbsoluteGravity(majorGravity, layoutDirection)) {
            case Gravity.RIGHT:
                // mTotalLength contains the padding already
                childLeft = mPaddingLeft + right - left - mTotalLength;
                break;

            case Gravity.CENTER_HORIZONTAL:
                // mTotalLength contains the padding already
                childLeft = mPaddingLeft + (right - left - mTotalLength) / 2;
                break;

            case Gravity.LEFT:
            default:
                childLeft = mPaddingLeft;
                break;
        }

        int start = 0;
        int dir = 1;
        //In case of RTL, start drawing from the last child.
        if (isLayoutRtl) {
            start = count - 1;
            dir = -1;
        }

        for (int i = 0; i < count; i++) {
            int childIndex = start + dir * i;
            final View child = getVirtualChildAt(childIndex);

            if (child == null) {
                childLeft += measureNullChild(childIndex);
            } else if (child.getVisibility() != GONE) {
                final int childWidth = child.getMeasuredWidth();
                final int childHeight = child.getMeasuredHeight();
                int childBaseline = -1;

                final LinearLayout.LayoutParams lp =
                        (LinearLayout.LayoutParams) child.getLayoutParams();

                if (baselineAligned && lp.height != LayoutParams.MATCH_PARENT) {
                    childBaseline = child.getBaseline();
                }

                int gravity = lp.gravity;
                if (gravity < 0) {
                    gravity = minorGravity;
                }

                switch (gravity & Gravity.VERTICAL_GRAVITY_MASK) {
                    case Gravity.TOP:
                        childTop = paddingTop + lp.topMargin;
                        if (childBaseline != -1) {
                            childTop += maxAscent[INDEX_TOP] - childBaseline;
                        }
                        break;

                    case Gravity.CENTER_VERTICAL:
                        // Removed support for baseline alignment when layout_gravity or
                        // gravity == center_vertical. See bug #1038483.
                        // Keep the code around if we need to re-enable this feature
                        // if (childBaseline != -1) {
                        //     // Align baselines vertically only if the child is smaller than us
                        //     if (childSpace - childHeight > 0) {
                        //         childTop = paddingTop + (childSpace / 2) - childBaseline;
                        //     } else {
                        //         childTop = paddingTop + (childSpace - childHeight) / 2;
                        //     }
                        // } else {
                        childTop = paddingTop + ((childSpace - childHeight) / 2)
                                + lp.topMargin - lp.bottomMargin;
                        break;

                    case Gravity.BOTTOM:
                        childTop = childBottom - childHeight - lp.bottomMargin;
                        if (childBaseline != -1) {
                            int descent = child.getMeasuredHeight() - childBaseline;
                            childTop -= (maxDescent[INDEX_BOTTOM] - descent);
                        }
                        break;
                    default:
                        childTop = paddingTop;
                        break;
                }

                if (hasDividerBeforeChildAt(childIndex)) {
                    childLeft += mDividerWidth;
                }

                childLeft += lp.leftMargin;
                setChildFrame(child, childLeft + getLocationOffset(child), childTop,
                        childWidth, childHeight);
                childLeft += childWidth + lp.rightMargin +
                        getNextLocationOffset(child);

                i += getChildrenSkipCount(child, childIndex);
            }
        }
    }

    private void setChildFrame(View child, int left, int top, int width, int height) {
        child.layout(left, top, left + width, top + height);
    }

    /**
     * Should the layout be a column or a row.
     * @param orientation Pass HORIZONTAL or VERTICAL. Default
     * value is HORIZONTAL.
     *
     * @attr ref android.R.styleable#LinearLayout_orientation
     */
    public void setOrientation(int orientation) {
        if (mOrientation != orientation) {
            mOrientation = orientation;
            requestLayout();
        }
    }

    /**
     * Returns the current orientation.
     *
     * @return either {@link #HORIZONTAL} or {@link #VERTICAL}
     */
    public int getOrientation() {
        return mOrientation;
    }

    /**
     * Describes how the child views are positioned. Defaults to GRAVITY_TOP. If
     * this layout has a VERTICAL orientation, this controls where all the child
     * views are placed if there is extra vertical space. If this layout has a
     * HORIZONTAL orientation, this controls the alignment of the children.
     *
     * @param gravity See {@link android.view.Gravity}
     *
     * @attr ref android.R.styleable#LinearLayout_gravity
     */
    @android.view.RemotableViewMethod
    public void setGravity(int gravity) {
        if (mGravity != gravity) {
            if ((gravity & Gravity.RELATIVE_HORIZONTAL_GRAVITY_MASK) == 0) {
                gravity |= Gravity.START;
            }

            if ((gravity & Gravity.VERTICAL_GRAVITY_MASK) == 0) {
                gravity |= Gravity.TOP;
            }

            mGravity = gravity;
            requestLayout();
        }
    }

    @android.view.RemotableViewMethod
    public void setHorizontalGravity(int horizontalGravity) {
        final int gravity = horizontalGravity & Gravity.RELATIVE_HORIZONTAL_GRAVITY_MASK;
        if ((mGravity & Gravity.RELATIVE_HORIZONTAL_GRAVITY_MASK) != gravity) {
            mGravity = (mGravity & ~Gravity.RELATIVE_HORIZONTAL_GRAVITY_MASK) | gravity;
            requestLayout();
        }
    }

    @android.view.RemotableViewMethod
    public void setVerticalGravity(int verticalGravity) {
        final int gravity = verticalGravity & Gravity.VERTICAL_GRAVITY_MASK;
        if ((mGravity & Gravity.VERTICAL_GRAVITY_MASK) != gravity) {
            mGravity = (mGravity & ~Gravity.VERTICAL_GRAVITY_MASK) | gravity;
            requestLayout();
        }
    }

    @Override
    public LayoutParams generateLayoutParams(AttributeSet attrs) {
        return new LinearLayout.LayoutParams(getContext(), attrs);
    }

    /**
     * Returns a set of layout parameters with a width of
     * {@link android.view.ViewGroup.LayoutParams#MATCH_PARENT}
     * and a height of {@link android.view.ViewGroup.LayoutParams#WRAP_CONTENT}
     * when the layout's orientation is {@link #VERTICAL}. When the orientation is
     * {@link #HORIZONTAL}, the width is set to {@link LayoutParams#WRAP_CONTENT}
     * and the height to {@link LayoutParams#WRAP_CONTENT}.
     */
    @Override
    protected LayoutParams generateDefaultLayoutParams() {
        if (mOrientation == HORIZONTAL) {
            return new LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
        } else if (mOrientation == VERTICAL) {
            return new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT);
        }
        return null;
    }

    @Override
    protected LayoutParams generateLayoutParams(ViewGroup.LayoutParams p) {
        return new LayoutParams(p);
    }


    // Override to allow type-checking of LayoutParams.
    @Override
    protected boolean checkLayoutParams(ViewGroup.LayoutParams p) {
        return p instanceof LinearLayout.LayoutParams;
    }

    @Override
    public void onInitializeAccessibilityEvent(AccessibilityEvent event) {
        super.onInitializeAccessibilityEvent(event);
        event.setClassName(LinearLayout.class.getName());
    }

    @Override
    public void onInitializeAccessibilityNodeInfo(AccessibilityNodeInfo info) {
        super.onInitializeAccessibilityNodeInfo(info);
        info.setClassName(LinearLayout.class.getName());
    }

    /**
     * Per-child layout information associated with ViewLinearLayout.
     *
     * @attr ref android.R.styleable#LinearLayout_Layout_layout_weight
     * @attr ref android.R.styleable#LinearLayout_Layout_layout_gravity
     */
    public static class LayoutParams extends ViewGroup.MarginLayoutParams {
        /**
         * Indicates how much of the extra space in the LinearLayout will be
         * allocated to the view associated with these LayoutParams. Specify
         * 0 if the view should not be stretched. Otherwise the extra pixels
         * will be pro-rated among all views whose weight is greater than 0.
         */
        @ViewDebug.ExportedProperty(category = "layout")
        public float weight;

        /**
         * Gravity for the view associated with these LayoutParams.
         *
         * @see android.view.Gravity
         */
        @ViewDebug.ExportedProperty(category = "layout", mapping = {
            @ViewDebug.IntToString(from =  -1,                       to = "NONE"),
            @ViewDebug.IntToString(from = Gravity.NO_GRAVITY,        to = "NONE"),
            @ViewDebug.IntToString(from = Gravity.TOP,               to = "TOP"),
            @ViewDebug.IntToString(from = Gravity.BOTTOM,            to = "BOTTOM"),
            @ViewDebug.IntToString(from = Gravity.LEFT,              to = "LEFT"),
            @ViewDebug.IntToString(from = Gravity.RIGHT,             to = "RIGHT"),
            @ViewDebug.IntToString(from = Gravity.START,            to = "START"),
            @ViewDebug.IntToString(from = Gravity.END,             to = "END"),
            @ViewDebug.IntToString(from = Gravity.CENTER_VERTICAL,   to = "CENTER_VERTICAL"),
            @ViewDebug.IntToString(from = Gravity.FILL_VERTICAL,     to = "FILL_VERTICAL"),
            @ViewDebug.IntToString(from = Gravity.CENTER_HORIZONTAL, to = "CENTER_HORIZONTAL"),
            @ViewDebug.IntToString(from = Gravity.FILL_HORIZONTAL,   to = "FILL_HORIZONTAL"),
            @ViewDebug.IntToString(from = Gravity.CENTER,            to = "CENTER"),
            @ViewDebug.IntToString(from = Gravity.FILL,              to = "FILL")
        })
        public int gravity = -1;

        /**
         * {@inheritDoc}
         */
        public LayoutParams(Context c, AttributeSet attrs) {
            super(c, attrs);
            TypedArray a =
                    c.obtainStyledAttributes(attrs, com.android.internal.R.styleable.LinearLayout_Layout);

            weight = a.getFloat(com.android.internal.R.styleable.LinearLayout_Layout_layout_weight, 0);
            gravity = a.getInt(com.android.internal.R.styleable.LinearLayout_Layout_layout_gravity, -1);

            a.recycle();
        }

        /**
         * {@inheritDoc}
         */
        public LayoutParams(int width, int height) {
            super(width, height);
            weight = 0;
        }

        /**
         * Creates a new set of layout parameters with the specified width, height
         * and weight.
         *
         * @param width the width, either {@link #MATCH_PARENT},
         *        {@link #WRAP_CONTENT} or a fixed size in pixels
         * @param height the height, either {@link #MATCH_PARENT},
         *        {@link #WRAP_CONTENT} or a fixed size in pixels
         * @param weight the weight
         */
        public LayoutParams(int width, int height, float weight) {
            super(width, height);
            this.weight = weight;
        }

        /**
         * {@inheritDoc}
         */
        public LayoutParams(ViewGroup.LayoutParams p) {
            super(p);
        }

        /**
         * {@inheritDoc}
         */
        public LayoutParams(ViewGroup.MarginLayoutParams source) {
            super(source);
        }

        /**
         * Copy constructor. Clones the width, height, margin values, weight,
         * and gravity of the source.
         *
         * @param source The layout params to copy from.
         */
        public LayoutParams(LayoutParams source) {
            super(source);

            this.weight = source.weight;
            this.gravity = source.gravity;
        }

        @Override
        public String debug(String output) {
            return output + "LinearLayout.LayoutParams={width=" + sizeToString(width) +
                    ", height=" + sizeToString(height) + " weight=" + weight +  "}";
        }
    }
}