@Override
public boolean dispatchTouchEvent(MotionEvent event) {
    if (event.getAction() == MotionEvent.ACTION_UP) {
        float per = Math.abs(mAppBarLayout.getY()) / mAppBarLayout.getTotalScrollRange();
        boolean setExpanded = (per <= 0.5F);
        mAppBarLayout.setExpanded(setExpanded,true);
    }
    return super.dispatchTouchEvent(event);
}

关于自动滚动到最后的位置,我在GitHub上放了一些代码,显示如何programmatically smooth scroll to a specific location可能有帮助.调用滚动到list.size() – 1在一个逃跑的例子可以复制的行为.这部分代码的方式是从StylingAndroid和Novoda博客改编：

public class RecyclerLayoutManager extends LinearLayoutManager {

    private AppBarManager mAppBarManager;
    private int visibleHeightForRecyclerView;

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

    @Override
    public void smoothScrollToPosition(RecyclerView recyclerView,RecyclerView.State state,int position) {
        View firstVisibleChild = recyclerView.getChildAt(0);
        final int childHeight = firstVisibleChild.getHeight();
        int distanceInPixels = ((findFirstVisibleItemPosition() - position) * childHeight);
        if (distanceInPixels == 0) {
            distanceInPixels = (int) Math.abs(firstVisibleChild.getY());
        }
        //Called Once
        if (visibleHeightForRecyclerView == 0) {
            visibleHeightForRecyclerView = mAppBarManager.getVisibleHeightForRecyclerViewInPx();
        }
        //Subtract one as adapter position 0 based
        final int visibleChildCount = visibleHeightForRecyclerView/childHeight - 1;

        if (position <= visibleChildCount) {
            //Scroll to the very top and expand the app bar
            position = 0;
            mAppBarManager.expandAppBar();
        } else {
            mAppBarManager.collapseAppBar();
        }

        SmoothScroller smoothScroller = new SmoothScroller(recyclerView.getContext(),Math.abs(distanceInPixels),1000);
        smoothScroller.setTargetPosition(position);
        startSmoothScroll(smoothScroller);
    }

    public void setAppBarManager(AppBarManager appBarManager) {
        mAppBarManager = appBarManager;
    }

    private class SmoothScroller extends LinearSmoothScroller {
        private static final int TARGET_SEEK_SCROLL_DISTANCE_PX = 10000;
        private final float distanceInPixels;
        private final float duration;

        public SmoothScroller(Context context,int distanceInPixels,int duration) {
            super(context);
            this.distanceInPixels = distanceInPixels;
            float millisecondsPerPx = calculateSpeedPerPixel(context.getResources().getDisplayMetrics());
            this.duration = distanceInPixels < TARGET_SEEK_SCROLL_DISTANCE_PX ?
                    (int) (Math.abs(distanceInPixels) * millisecondsPerPx) : duration;
        }

        @Override
        public PointF computeScrollVectorForPosition(int targetPosition) {
            return RecyclerLayoutManager.this
                    .computeScrollVectorForPosition(targetPosition);
        }

        @Override
        protected int calculateTimeForScrolling(int dx) {
            float proportion = (float) dx / distanceInPixels;
            return (int) (duration * proportion);
        }
    }
}

编辑：

以上代码片段中的AppBarManager是指用于与活动中的AppBarLayout通信的界面.使用动画来折叠/展开应用程序栏方法.最终的方法用于计算屏幕上可见的RecyclerView行数：

AppBarManager.java

public interface AppBarManager {

    void collapseAppBar();
    void expandAppBar();
    int getVisibleHeightForRecyclerViewInPx();

}

MainActivity.java

public class MainActivity extends AppCompatActivity implements AppBarManager{

@Override
public void collapseAppBar() {
    mAppBarLayout.setExpanded(false,true);
}

@Override
public void expandAppBar() {
    mAppBarLayout.setExpanded(true,true);
}

@Override
public int getVisibleHeightForRecyclerViewInPx() {

    if (mRecyclerFragment == null) mRecyclerFragment =
            (RecyclerFragment) getSupportFragmentManager().findFragmentByTag(RecyclerFragment.TAG);

    int windowHeight,appBarHeight,headerViewHeight;
    windowHeight = getWindow().getDecorView().getHeight();
    appBarHeight = mAppBarLayout.getHeight();
    headerViewHeight = mRecyclerFragment.getHeaderView().getHeight();
    return windowHeight - (appBarHeight + headerViewHeight);
}