appcompat/widget/AlertDialogLayout.java

/*
 * Copyright (C) 2016 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 androidx.appcompat.widget;

import static androidx.annotation.RestrictTo.Scope.LIBRARY_GROUP;

import android.content.Context;
import android.graphics.drawable.Drawable;
import android.util.AttributeSet;
import android.view.Gravity;
import android.view.View;
import android.view.ViewGroup;

import androidx.annotation.Nullable;
import androidx.annotation.RestrictTo;
import androidx.appcompat.R;
import androidx.core.view.GravityCompat;
import androidx.core.view.ViewCompat;

/**
 * Special implementation of linear layout that's capable of laying out alert
 * dialog components.
 * <p>
 * A dialog consists of up to three panels. All panels are optional, and a
 * dialog may contain only a single panel. The panels are laid out according
 * to the following guidelines:
 * <ul>
 *     <li>topPanel: exactly wrap_content</li>
 *     <li>contentPanel OR customPanel: at most fill_parent, first priority for
 *         extra space</li>
 *     <li>buttonPanel: at least minHeight, at most wrap_content, second
 *         priority for extra space</li>
 * </ul>
 *
 * @hide
 */
@RestrictTo(LIBRARY_GROUP)
public class AlertDialogLayout extends LinearLayoutCompat {

    public AlertDialogLayout(@Nullable Context context) {
        super(context);
    }

    public AlertDialogLayout(@Nullable Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        if (!tryOnMeasure(widthMeasureSpec, heightMeasureSpec)) {
            // Failed to perform custom measurement, let superclass handle it.
            super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        }
    }

    private boolean tryOnMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        View topPanel = null;
        View buttonPanel = null;
        View middlePanel = null;

        final int count = getChildCount();
        for (int i = 0; i < count; i++) {
            final View child = getChildAt(i);
            if (child.getVisibility() == View.GONE) {
                continue;
            }

            final int id = child.getId();
            if (id == R.id.topPanel) {
                topPanel = child;
            } else if (id == R.id.buttonPanel) {
                buttonPanel = child;
            } else if (id == R.id.contentPanel || id == R.id.customPanel) {
                if (middlePanel != null) {
                    // Both the content and custom are visible. Abort!
                    return false;
                }
                middlePanel = child;
            } else {
                // Unknown top-level child. Abort!
                return false;
            }
        }

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

        int childState = 0;
        int usedHeight = getPaddingTop() + getPaddingBottom();

        if (topPanel != null) {
            topPanel.measure(widthMeasureSpec, MeasureSpec.UNSPECIFIED);

            usedHeight += topPanel.getMeasuredHeight();
            childState = View.combineMeasuredStates(childState, topPanel.getMeasuredState());
        }

        int buttonHeight = 0;
        int buttonWantsHeight = 0;
        if (buttonPanel != null) {
            buttonPanel.measure(widthMeasureSpec, MeasureSpec.UNSPECIFIED);
            buttonHeight = resolveMinimumHeight(buttonPanel);
            buttonWantsHeight = buttonPanel.getMeasuredHeight() - buttonHeight;

            usedHeight += buttonHeight;
            childState = View.combineMeasuredStates(childState, buttonPanel.getMeasuredState());
        }

        int middleHeight = 0;
        if (middlePanel != null) {
            final int childHeightSpec;
            if (heightMode == MeasureSpec.UNSPECIFIED) {
                childHeightSpec = MeasureSpec.UNSPECIFIED;
            } else {
                childHeightSpec = MeasureSpec.makeMeasureSpec(
                        Math.max(0, heightSize - usedHeight), heightMode);
            }

            middlePanel.measure(widthMeasureSpec, childHeightSpec);
            middleHeight = middlePanel.getMeasuredHeight();

            usedHeight += middleHeight;
            childState = View.combineMeasuredStates(childState, middlePanel.getMeasuredState());
        }

        int remainingHeight = heightSize - usedHeight;

        // Time for the "real" button measure pass. If we have remaining space,
        // make the button pane bigger up to its target height. Otherwise,
        // just remeasure the button at whatever height it needs.
        if (buttonPanel != null) {
            usedHeight -= buttonHeight;

            final int heightToGive = Math.min(remainingHeight, buttonWantsHeight);
            if (heightToGive > 0) {
                remainingHeight -= heightToGive;
                buttonHeight += heightToGive;
            }

            final int childHeightSpec = MeasureSpec.makeMeasureSpec(
                    buttonHeight, MeasureSpec.EXACTLY);
            buttonPanel.measure(widthMeasureSpec, childHeightSpec);

            usedHeight += buttonPanel.getMeasuredHeight();
            childState = View.combineMeasuredStates(childState, buttonPanel.getMeasuredState());
        }

        // If we still have remaining space, make the middle pane bigger up
        // to the maximum height.
        if (middlePanel != null && remainingHeight > 0) {
            usedHeight -= middleHeight;

            final int heightToGive = remainingHeight;
            remainingHeight -= heightToGive;
            middleHeight += heightToGive;

            // Pass the same height mode as we're using for the dialog itself.
            // If it's EXACTLY, then the middle pane MUST use the entire
            // height.
            final int childHeightSpec = MeasureSpec.makeMeasureSpec(
                    middleHeight, heightMode);
            middlePanel.measure(widthMeasureSpec, childHeightSpec);

            usedHeight += middlePanel.getMeasuredHeight();
            childState = View.combineMeasuredStates(childState, middlePanel.getMeasuredState());
        }

        // Compute desired width as maximum child width.
        int maxWidth = 0;
        for (int i = 0; i < count; i++) {
            final View child = getChildAt(i);
            if (child.getVisibility() != View.GONE) {
                maxWidth = Math.max(maxWidth, child.getMeasuredWidth());
            }
        }

        maxWidth += getPaddingLeft() + getPaddingRight();

        final int widthSizeAndState = View.resolveSizeAndState(
                maxWidth, widthMeasureSpec, childState);
        final int heightSizeAndState = View.resolveSizeAndState(
                usedHeight, heightMeasureSpec, 0);
        setMeasuredDimension(widthSizeAndState, heightSizeAndState);

        // If the children weren't already measured EXACTLY, we need to run
        // another measure pass to for MATCH_PARENT widths.
        if (widthMode != MeasureSpec.EXACTLY) {
            forceUniformWidth(count, heightMeasureSpec);
        }

        return true;
    }

    /**
     * Remeasures child views to exactly match the layout's measured width.
     *
     * @param count the number of child views
     * @param heightMeasureSpec the original height measure spec
     */
    private void forceUniformWidth(int count, int heightMeasureSpec) {
        // Pretend that the linear layout has an exact size.
        final int uniformMeasureSpec = MeasureSpec.makeMeasureSpec(
                getMeasuredWidth(), MeasureSpec.EXACTLY);

        for (int i = 0; i < count; i++) {
            final View child = getChildAt(i);
            if (child.getVisibility() != GONE) {
                final LayoutParams lp = (LayoutParams) child.getLayoutParams();
                if (lp.width == LayoutParams.MATCH_PARENT) {
                    // Temporarily force children to reuse their old measured
                    // height.
                    final int oldHeight = lp.height;
                    lp.height = child.getMeasuredHeight();

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

    /**
     * Attempts to resolve the minimum height of a view.
     * <p>
     * If the view doesn't have a minimum height set and only contains a single
     * child, attempts to resolve the minimum height of the child view.
     *
     * @param v the view whose minimum height to resolve
     * @return the minimum height
     */
    private static int resolveMinimumHeight(View v) {
        final int minHeight = ViewCompat.getMinimumHeight(v);
        if (minHeight > 0) {
            return minHeight;
        }

        if (v instanceof ViewGroup) {
            final ViewGroup vg = (ViewGroup) v;
            if (vg.getChildCount() == 1) {
                return resolveMinimumHeight(vg.getChildAt(0));
            }
        }

        return 0;
    }

    @Override
    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
        final int paddingLeft = getPaddingLeft();

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

        // Space available for child
        final int childSpace = width - paddingLeft - getPaddingRight();

        final int totalLength = getMeasuredHeight();
        final int count = getChildCount();
        final int gravity = getGravity();
        final int majorGravity = gravity & Gravity.VERTICAL_GRAVITY_MASK;
        final int minorGravity = gravity & GravityCompat.RELATIVE_HORIZONTAL_GRAVITY_MASK;

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

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

            case Gravity.TOP:
            default:
                childTop = getPaddingTop();
                break;
        }

        final Drawable dividerDrawable = getDividerDrawable();
        final int dividerHeight = dividerDrawable == null ?
                0 : dividerDrawable.getIntrinsicHeight();

        for (int i = 0; i < count; i++) {
            final View child = getChildAt(i);
            if (child != null && child.getVisibility() != GONE) {
                final int childWidth = child.getMeasuredWidth();
                final int childHeight = child.getMeasuredHeight();

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

                int layoutGravity = lp.gravity;
                if (layoutGravity < 0) {
                    layoutGravity = minorGravity;
                }
                final int layoutDirection = ViewCompat.getLayoutDirection(this);
                final int absoluteGravity = GravityCompat.getAbsoluteGravity(
                        layoutGravity, layoutDirection);

                final int childLeft;
                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 += dividerHeight;
                }

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

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