GridLayoutQuirksFixedManager.java

package android.support.v7.widget;

import android.content.Context;
import android.util.AttributeSet;
import android.view.View;

/**
 * Bug fixed version of GridLayoutManager
 * Created by SangsooNam on 20/09/15.
 * Modified by Cain Wong on 13/11/15: Updated for Recyclerview-v7:22.2.1
 * <p/>
 * --- Bug ---
 * <br>
 * https://code.google.com/p/android/issues/detail?id=182517
 * <br>
 * After calling `scrollToPosition`, only first grid column is shown and others are shown in
 * the other row. This is due to wrong `anchorInfo.mPosition`. There are two modes depending on the
 * value `anchorInfo.mLayoutFromEnd`. One is to layout from start to end, and the other is to layout
 * from end to start. When to layout from start to end, `ensureAnchorInFirstSpan` is reasonable.
 * However, it doesn't make sense when to layout from end to start. At that time, we need to ensure
 * that anchor is in the last span instead of the first. This class is fixing that issue.
 */
public class GridLayoutQuirksFixedManager extends GridLayoutManager {

    public GridLayoutQuirksFixedManager(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
        super(context, attrs, defStyleAttr, defStyleRes);
    }

    public GridLayoutQuirksFixedManager(Context context, int spanCount) {
        super(context, spanCount);
    }

    public GridLayoutQuirksFixedManager(Context context, int spanCount, int orientation, boolean reverseLayout) {
        super(context, spanCount, orientation, reverseLayout);
    }

    @Override
    void onAnchorReady(RecyclerView.Recycler recycler, RecyclerView.State state,
                       AnchorInfo anchorInfo) {
        super.onAnchorReady(recycler, state, anchorInfo);
        updateMeasurements();
        if (state.getItemCount() > 0 && !state.isPreLayout()) {
            if (anchorInfo.mLayoutFromEnd) {
                ensureAnchorIsInLastSpan(recycler, state, anchorInfo);
            } else {
                ensureAnchorIsInFirstSpan(recycler, state, anchorInfo);
            }
        }
        if (mSet == null || mSet.length != mSpanCount) {
            mSet = new View[mSpanCount];
        }
    }

    private void ensureAnchorIsInLastSpan(RecyclerView.Recycler recycler, RecyclerView.State state,
                                          AnchorInfo anchorInfo) {
        int spanIndex = getSpanIndex(recycler, state, anchorInfo.mPosition);
        int spanSize = mSpanSizeLookup.getSpanSize(anchorInfo.mPosition);
        while (spanIndex + spanSize < mSpanCount && anchorInfo.mPosition < getItemCount()) {
            anchorInfo.mPosition++;
            spanIndex = mSpanSizeLookup.getCachedSpanIndex(anchorInfo.mPosition, mSpanCount);
            spanSize = mSpanSizeLookup.getSpanSize(anchorInfo.mPosition);
        }
    }

    /**
     * The same code from GridLayoutManager
     */
    private void ensureAnchorIsInFirstSpan(RecyclerView.Recycler recycler, RecyclerView.State state,
                                           AnchorInfo anchorInfo) {
        int span = getSpanIndex(recycler, state, anchorInfo.mPosition);
        while (span > 0 && anchorInfo.mPosition > 0) {
            anchorInfo.mPosition--;
            span = getSpanIndex(recycler, state, anchorInfo.mPosition);
        }
    }

    /**
     * The same code from GridLayoutManager except commented out logging
     */
    private int getSpanIndex(RecyclerView.Recycler recycler, RecyclerView.State state, int pos) {
        if (!state.isPreLayout()) {
            return mSpanSizeLookup.getCachedSpanIndex(pos, mSpanCount);
        }
        final int cached = mPreLayoutSpanIndexCache.get(pos, -1);
        if (cached != -1) {
            return cached;
        }
        final int adapterPosition = recycler.convertPreLayoutPositionToPostLayout(pos);
        if (adapterPosition == -1) {
//            if (DEBUG) {
//                throw new RuntimeException("Cannot find span index for pre layout position. It is"
//                        + " not cached, not in the adapter. Pos:" + pos);
//            }
//            Log.w(TAG, "Cannot find span size for pre layout position. It is"
//                    + " not cached, not in the adapter. Pos:" + pos);
            return 0;
        }
        return mSpanSizeLookup.getCachedSpanIndex(adapterPosition, mSpanCount);
    }


    /**
     * The same code from GridLayoutManager
     */
    private void updateMeasurements() {
        int totalSpace;
        if (getOrientation() == VERTICAL) {
            totalSpace = getWidth() - getPaddingRight() - getPaddingLeft();
        } else {
            totalSpace = getHeight() - getPaddingBottom() - getPaddingTop();
        }
        calculateItemBorders(totalSpace);
    }


    /**
     * The same code from GridLayoutManager
     */
    private void calculateItemBorders(int totalSpace) {
        if (mCachedBorders == null || mCachedBorders.length != mSpanCount + 1
                || mCachedBorders[mCachedBorders.length - 1] != totalSpace) {
            mCachedBorders = new int[mSpanCount + 1];
        }
        mCachedBorders[0] = 0;
        int sizePerSpan = totalSpace / mSpanCount;
        int sizePerSpanRemainder = totalSpace % mSpanCount;
        int consumedPixels = 0;
        int additionalSize = 0;
        for (int i = 1; i <= mSpanCount; i++) {
            int itemSize = sizePerSpan;
            additionalSize += sizePerSpanRemainder;
            if (additionalSize > 0 && (mSpanCount - additionalSize) < sizePerSpanRemainder) {
                itemSize += 1;
                additionalSize -= mSpanCount;
            }
            consumedPixels += itemSize;
            mCachedBorders[i] = consumedPixels;
        }
    }

}