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      1 /*
      2  * Copyright 2018 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 package androidx.recyclerview.widget;
     18 
     19 import android.view.View;
     20 
     21 /**
     22  * Helper class that keeps temporary state while {LayoutManager} is filling out the empty
     23  * space.
     24  */
     25 class LayoutState {
     26 
     27     static final String TAG = "LayoutState";
     28 
     29     static final int LAYOUT_START = -1;
     30 
     31     static final int LAYOUT_END = 1;
     32 
     33     static final int INVALID_LAYOUT = Integer.MIN_VALUE;
     34 
     35     static final int ITEM_DIRECTION_HEAD = -1;
     36 
     37     static final int ITEM_DIRECTION_TAIL = 1;
     38 
     39     /**
     40      * We may not want to recycle children in some cases (e.g. layout)
     41      */
     42     boolean mRecycle = true;
     43 
     44     /**
     45      * Number of pixels that we should fill, in the layout direction.
     46      */
     47     int mAvailable;
     48 
     49     /**
     50      * Current position on the adapter to get the next item.
     51      */
     52     int mCurrentPosition;
     53 
     54     /**
     55      * Defines the direction in which the data adapter is traversed.
     56      * Should be {@link #ITEM_DIRECTION_HEAD} or {@link #ITEM_DIRECTION_TAIL}
     57      */
     58     int mItemDirection;
     59 
     60     /**
     61      * Defines the direction in which the layout is filled.
     62      * Should be {@link #LAYOUT_START} or {@link #LAYOUT_END}
     63      */
     64     int mLayoutDirection;
     65 
     66     /**
     67      * This is the target pixel closest to the start of the layout that we are trying to fill
     68      */
     69     int mStartLine = 0;
     70 
     71     /**
     72      * This is the target pixel closest to the end of the layout that we are trying to fill
     73      */
     74     int mEndLine = 0;
     75 
     76     /**
     77      * If true, layout should stop if a focusable view is added
     78      */
     79     boolean mStopInFocusable;
     80 
     81     /**
     82      * If the content is not wrapped with any value
     83      */
     84     boolean mInfinite;
     85 
     86     /**
     87      * @return true if there are more items in the data adapter
     88      */
     89     boolean hasMore(RecyclerView.State state) {
     90         return mCurrentPosition >= 0 && mCurrentPosition < state.getItemCount();
     91     }
     92 
     93     /**
     94      * Gets the view for the next element that we should render.
     95      * Also updates current item index to the next item, based on {@link #mItemDirection}
     96      *
     97      * @return The next element that we should render.
     98      */
     99     View next(RecyclerView.Recycler recycler) {
    100         final View view = recycler.getViewForPosition(mCurrentPosition);
    101         mCurrentPosition += mItemDirection;
    102         return view;
    103     }
    104 
    105     @Override
    106     public String toString() {
    107         return "LayoutState{"
    108                 + "mAvailable=" + mAvailable
    109                 + ", mCurrentPosition=" + mCurrentPosition
    110                 + ", mItemDirection=" + mItemDirection
    111                 + ", mLayoutDirection=" + mLayoutDirection
    112                 + ", mStartLine=" + mStartLine
    113                 + ", mEndLine=" + mEndLine
    114                 + '}';
    115     }
    116 }
    117