Vertical Scrolling CoordinatorLayout Behavior for BottomNavigationView with RecyclerView vertical scrolling

Question

How to define a CoordinatorLayout.Behavior class for BottomNavigationView which scrolls synchronized with the RecyclerView veritical scroll.

I have seen this and this, but all it does is just show/hide the NavigationView on veritical scroll events immediately. I don't want to show/hide the NavigationView immediately, instead i want a behavior something like the AppbarLayout having a Toolbar with scroll flag as app:layout_scrollFlags="scroll|enterAlways".

 public class BottomNavigationBehavior extends CoordinatorLayout.Behavior<BottomNavigationView> {

    public BottomNavigationBehavior() {
        super();
    }

    public BottomNavigationBehavior(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    @Override
    public boolean layoutDependsOn(CoordinatorLayout parent, BottomNavigationView child, View dependency) {
        boolean dependsOn = dependency instanceof FrameLayout;
        return dependsOn;
    }

    @Override
    public boolean onStartNestedScroll(CoordinatorLayout coordinatorLayout, BottomNavigationView child, View directTargetChild, View target, int nestedScrollAxes) {
        return nestedScrollAxes == ViewCompat.SCROLL_AXIS_VERTICAL;
    }

    @Override
    public void onNestedPreScroll(CoordinatorLayout coordinatorLayout, BottomNavigationView child, View target, int dx, int dy, int[] consumed) {
        if(dy < 0) {
            showBottomNavigationView(child);
        }
        else if(dy > 0) {
            hideBottomNavigationView(child);
        }
    }

    private void hideBottomNavigationView(BottomNavigationView view) {
        view.animate().translationY(view.getHeight());
    }

    private void showBottomNavigationView(BottomNavigationView view) {
        view.animate().translationY(0);
    }
}

Answer 1

After some trying I came up with this solution:

  recyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
                @Override
                public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                    super.onScrolled(recyclerView, dx, dy);
                    if(dy > 0 && visible){
                        mBinding.bnv.test.setY(mBinding.bnv.getY() + dy);
                        DisplayMetrics metrics = new DisplayMetrics();
                        getActivity().getWindowManager().getDefaultDisplay().getMetrics(metrics);
                        visible = mBiding.bnv.getY() > metrics.heightPixels;
                        if(!visible) {
                            mBinding.bnv.setY(metrics.heightPixels);
                        }
                    } else {
                        mBinding.bnv.setY(mBinding.bnv.getY() + dy);
                        DisplayMetrics metrics = new DisplayMetrics();
                        getActivity().getWindowManager().getDefaultDisplay().getMetrics(metrics);
                        visible = mBinding.bnv.getY() > metrics.heightPixels;
                    }
        }

So you are scrollling the BottomNavigationView with the recycler view

Or with CoordinatorLayout.Behavior class:

public class ViewScrollWithRecyclerViewBehavior extends CoordinatorLayout.Behavior<View> {
    private boolean visible = true;
    private boolean inStartPosition = true;
    private float oldY;
    private DisplayMetrics metrics;



    public ViewScrollWithRecyclerViewBehavior(Context context, AttributeSet attrs) {
        super(context, attrs);
        metrics = Resources.getSystem().getDisplayMetrics();
    }

    @Override
    public boolean layoutDependsOn(CoordinatorLayout parent, View fab, View dependency) {
        return dependency instanceof AppBarLayout;
    }

    @Override
    public boolean onDependentViewChanged(CoordinatorLayout parent, View child, View dependency) {
        if (dependency instanceof AppBarLayout) {
            CoordinatorLayout.LayoutParams lp = (CoordinatorLayout.LayoutParams) child.getLayoutParams();
            float dy  = oldY - dependency.getY();
            if(dy > 0 && visible){
                moveDown(child, oldY);
            } else if(!inStartPosition) {
               moveUp(child, oldY);
            }
            oldY = dependency.getY();
        }
        return true;
    }

    private void moveUp(View child, float dy){
        if(child.getY() + dy >= metrics.heightPixels - child.getHeight()){
            child.setY(metrics.heightPixels - child.getHeight());
        } else {
            child.setY(child.getY() + dy);
        }
        inStartPosition = child.getY() == metrics.heightPixels - child.getHeight();
        visible = child.getY() > metrics.heightPixels;
    }


    private void moveDown(View child, float dy){
        child.setY(child.getY() + dy);

        visible = child.getY() > metrics.heightPixels;
        if(!visible) {
            child.setY(metrics.heightPixels);
        }
    }

    @Override
    public boolean onStartNestedScroll(final CoordinatorLayout coordinatorLayout, final View child,
                                       final View directTargetChild, final View target, final int nestedScrollAxes) {
        return true;
    }

    @Override
    public void onNestedScroll(final CoordinatorLayout coordinatorLayout,
                               final View child,
                               final View target, final int dxConsumed, final int dy,
                               final int dxUnconsumed, final int dyUnconsumed) {
        super.onNestedScroll(coordinatorLayout, child, target, dxConsumed, dy, dxUnconsumed, dyUnconsumed);
        if(dy > 0 && visible){
           moveDown(child, dy);
        } else if(!inStartPosition) {
          moveUp(child, dy);
        }
    }


}