Flinging with RecyclerView + AppBarLayout

I am using the new CoordinatorLayout with AppBarLayout and CollapsingToolbarLayout. Below AppBarLayout, I have a RecyclerView with a list of content.

I have verified that fling scrolling works on the RecyclerView when I am scrolling up and down the list. However, I would also like the AppBarLayout to smoothly scroll during expansion.

When scrolling up to expand the CollaspingToolbarLayout, scrolling immediately stops once lifting your finger off the screen. If you scroll up in a quick motion, sometimes the CollapsingToolbarLayout re-collapses as well. This behavior with the RecyclerView seems to function much differently than when using a NestedScrollView.

I've tried to set different scroll properties on the recyclerview but I haven't been able to figure this out.

Here is a video showing some of the scrolling issues. https://youtu.be/xMLKoJOsTAM

Here is an example showing the issue with the RecyclerView (CheeseDetailActivity). https://github.com/tylerjroach/cheesesquare

Here is the original example that uses a NestedScrollView from Chris Banes. https://github.com/chrisbanes/cheesesquare

The answer of Kirill Boyarshinov was almost correct.

The main problem is that the RecyclerView sometimes is giving incorrect fling direction, so if you add the following code to his answer it works correctly:

public final class FlingBehavior extends AppBarLayout.Behavior {
    private static final int TOP_CHILD_FLING_THRESHOLD = 3;
    private boolean isPositive;

    public FlingBehavior() {
    }

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

    @Override
    public boolean onNestedFling(CoordinatorLayout coordinatorLayout, AppBarLayout child, View target, float velocityX, float velocityY, boolean consumed) {
        if (velocityY > 0 && !isPositive || velocityY < 0 && isPositive) {
            velocityY = velocityY * -1;
        }
        if (target instanceof RecyclerView && velocityY < 0) {
            final RecyclerView recyclerView = (RecyclerView) target;
            final View firstChild = recyclerView.getChildAt(0);
            final int childAdapterPosition = recyclerView.getChildAdapterPosition(firstChild);
            consumed = childAdapterPosition > TOP_CHILD_FLING_THRESHOLD;
        }
        return super.onNestedFling(coordinatorLayout, child, target, velocityX, velocityY, consumed);
    }

    @Override
    public void onNestedPreScroll(CoordinatorLayout coordinatorLayout, AppBarLayout child, View target, int dx, int dy, int[] consumed) {
        super.onNestedPreScroll(coordinatorLayout, child, target, dx, dy, consumed);
        isPositive = dy > 0;
    }
}

I hope that this helps.

Seems that v23 update did not fix it yet.

I have found sort of of hack to fix it with flinging down. The trick is to reconsume fling event if ScrollingView's top child is close to the beginning of data in Adapter.

public final class FlingBehavior extends AppBarLayout.Behavior {

    public FlingBehavior() {
    }

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

    @Override
    public boolean onNestedFling(CoordinatorLayout coordinatorLayout, AppBarLayout child, View target, float velocityX, float velocityY, boolean consumed) {
        if (target instanceof ScrollingView) {
            final ScrollingView scrollingView = (ScrollingView) target;
            consumed = velocityY > 0 || scrollingView.computeVerticalScrollOffset() > 0;
        }
        return super.onNestedFling(coordinatorLayout, child, target, velocityX, velocityY, consumed);
    }
}

Use it in your layout like that:

 <android.support.design.widget.AppBarLayout
    android:id="@+id/appbar"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    app:layout_behavior="your.package.FlingBehavior">
    <!--your views here-->
 </android.support.design.widget.AppBarLayout>

EDIT: Fling event reconsuming is now based on verticalScrollOffset instead of amount of items on from top of RecyclerView.

EDIT2: Check target as ScrollingView interface instance instead of RecyclerView. Both RecyclerView and NestedScrollingView implement it.

I have found the fix by applying OnScrollingListener to the recyclerView. now it works very well. The issue is that recyclerview provided the wrong consumed value and the behavior doesn't know when the recyclerview is scrolled to the top.

package com.singmak.uitechniques.util.coordinatorlayout;

import android.content.Context;
import android.support.design.widget.AppBarLayout;
import android.support.design.widget.CoordinatorLayout;
import android.support.v7.widget.RecyclerView;
import android.util.AttributeSet;
import android.view.View;

import java.lang.ref.WeakReference;
import java.util.HashMap;
import java.util.Map;

/**
 * Created by maksing on 26/3/2016.
 */
public final class RecyclerViewAppBarBehavior extends AppBarLayout.Behavior {

    private Map<RecyclerView, RecyclerViewScrollListener> scrollListenerMap = new HashMap<>(); //keep scroll listener map, the custom scroll listener also keep the current scroll Y position.

    public RecyclerViewAppBarBehavior() {
    }

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

    /**
     *
     * @param coordinatorLayout
     * @param child The child that attached the behavior (AppBarLayout)
     * @param target The scrolling target e.g. a recyclerView or NestedScrollView
     * @param velocityX
     * @param velocityY
     * @param consumed The fling should be consumed by the scrolling target or not
     * @return
     */
    @Override
    public boolean onNestedFling(CoordinatorLayout coordinatorLayout, AppBarLayout child, View target, float velocityX, float velocityY, boolean consumed) {
        if (target instanceof RecyclerView) {
            final RecyclerView recyclerView = (RecyclerView) target;
            if (scrollListenerMap.get(recyclerView) == null) {
                RecyclerViewScrollListener recyclerViewScrollListener = new RecyclerViewScrollListener(coordinatorLayout, child, this);
                scrollListenerMap.put(recyclerView, recyclerViewScrollListener);
                recyclerView.addOnScrollListener(recyclerViewScrollListener);
            }
            scrollListenerMap.get(recyclerView).setVelocity(velocityY);
            consumed = scrollListenerMap.get(recyclerView).getScrolledY() > 0; //recyclerView only consume the fling when it's not scrolled to the top
        }
        return super.onNestedFling(coordinatorLayout, child, target, velocityX, velocityY, consumed);
    }

    private static class RecyclerViewScrollListener extends RecyclerView.OnScrollListener {
        private int scrolledY;
        private boolean dragging;
        private float velocity;
        private WeakReference<CoordinatorLayout> coordinatorLayoutRef;
        private WeakReference<AppBarLayout> childRef;
        private WeakReference<RecyclerViewAppBarBehavior> behaviorWeakReference;

        public RecyclerViewScrollListener(CoordinatorLayout coordinatorLayout, AppBarLayout child, RecyclerViewAppBarBehavior barBehavior) {
            coordinatorLayoutRef = new WeakReference<CoordinatorLayout>(coordinatorLayout);
            childRef = new WeakReference<AppBarLayout>(child);
            behaviorWeakReference = new WeakReference<RecyclerViewAppBarBehavior>(barBehavior);
        }

        @Override
        public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
            dragging = newState == RecyclerView.SCROLL_STATE_DRAGGING;
        }

        public void setVelocity(float velocity) {
            this.velocity = velocity;
        }

        public int getScrolledY() {
            return scrolledY;
        }

        @Override
        public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
            scrolledY += dy;

            if (scrolledY <= 0 && !dragging && childRef.get() != null && coordinatorLayoutRef.get() != null && behaviorWeakReference.get() != null) {
                //manually trigger the fling when it's scrolled at the top
                behaviorWeakReference.get().onNestedFling(coordinatorLayoutRef.get(), childRef.get(), recyclerView, 0, velocity, false);
            }
        }
    }
}

It has been fixed since support design 26.0.0.

compile 'com.android.support:design:26.0.0'

This is a smooth version of Google Support Design AppBarLayout. If you are using AppBarLayout, you will know it has an issue with fling.

compile "me.henrytao:smooth-app-bar-layout:<latest-version>"

See Library here.. https://github.com/henrytao-me/smooth-app-bar-layout