Android retractable or collapsed toolbar for chat view

Question

I'm using a collapsed toolbar for a chat view, everything working fine I have

app:layout_behavior="@string/appbar_scrolling_view_behavior"

on my recycler view and

app:layout_scrollFlags="scroll|enterAlways|snap"

on the retractable header

I'm using it for a chat view so the first element in recyclerView are at the bottom of the list due to

LinearLayoutManager layoutManager = new LinearLayoutManager(getActivity());
layoutManager.setReverseLayout(true);

The thing is I would like to hide header when I'm scrolling up and hide it when I'm scrolling down, the exact inverse of the actual behavior. And the header appears when I reach the top of the list, (the oldest message) instead I would like to make it visible when I reach the bottom when I'm showing the latest message

Answer 1

I found a solution I'm using the old way with OnScrollListener for retractable header and inverse it for fit to the reverse layout manager

public abstract class HidingScrollListener extends RecyclerView.OnScrollListener {

private static final float HIDE_THRESHOLD = 10;
private static final float SHOW_THRESHOLD = 70;

private int mToolbarOffset = 0;
private boolean mControlsVisible = true;
private int mToolbarHeight;
private int mTotalScrolledDistance;

public HidingScrollListener(int mToolbarHeight) {
    this.mToolbarHeight = mToolbarHeight;
}

@Override
public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
    super.onScrollStateChanged(recyclerView, newState);
    if (newState == RecyclerView.SCROLL_STATE_IDLE) {
        if (mTotalScrolledDistance < mToolbarHeight) {
            setVisible();
        } else {
            if (mControlsVisible) {
                if (mToolbarOffset > HIDE_THRESHOLD) {
                    setInvisible();
                } else {
                    setVisible();
                }
            } else {
                if ((mToolbarHeight - mToolbarOffset) > SHOW_THRESHOLD) {
                    setVisible();
                } else {
                    setInvisible();
                }
            }
        }
    }
}

@Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
    super.onScrolled(recyclerView, dx, dy);
    dy = dy * -1;
    clipToolbarOffset();
    onMoved(mToolbarOffset);
    if ((mToolbarOffset < mToolbarHeight && dy > 0) || (mToolbarOffset > 0 && dy < 0)) {
        mToolbarOffset += dy;
    }
    mTotalScrolledDistance += dy;

}

private void clipToolbarOffset() {
    if (mToolbarOffset > mToolbarHeight) {
        mToolbarOffset = mToolbarHeight;
    } else if (mToolbarOffset < 0) {
        mToolbarOffset = 0;
    }
}

private void setVisible() {
    if (mToolbarOffset > 0) {
        onShow();
        mToolbarOffset = 0;
    }
    mControlsVisible = true;
}

private void setInvisible() {
    if (mToolbarOffset < mToolbarHeight) {
        onHide();
        mToolbarOffset = mToolbarHeight;
    }
    mControlsVisible = false;
}

public abstract void onMoved(int distance);

public abstract void onShow();

public abstract void onHide();
}

And then I'm using it like this in my Fragment

  dataBinding.chatDetailRoot.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
        @Override
        public void onGlobalLayout() {
            mToolbarHeight = dataBinding.chatDetailAdsHeader.getHeight();
            dataBinding.chatDetailRecyclerView.addOnScrollListener(new HidingScrollListener(mToolbarHeight) {
                @Override
                public void onMoved(int distance) {
                    dataBinding.chatDetailAdsHeader.setTranslationY(-distance);
                }

                @Override
                public void onShow() {
                    dataBinding.chatDetailAdsHeader.animate().translationY(0).setInterpolator(new DecelerateInterpolator(2)).start();
                }

                @Override
                public void onHide() {
                    dataBinding.chatDetailAdsHeader.animate().translationY(-mToolbarHeight).setInterpolator(new AccelerateInterpolator(2)).start();
                }
            });
            dataBinding.chatDetailRoot.getViewTreeObserver().removeOnGlobalLayoutListener(this);
        }
    });
}

I'm using a viewTreeObserver because I need to get the toolbar height and chatDetailAdsHeader is my AppBarLayout component