Collapsing Toolbar bounces with error after supporting lib 26.0.0

Question

Since updating the Android support libraries from version 25.4.0 to 26.0.0 (to 27.0.0), I experience some strange behavior in the minimizing toolbar inside the action.

See the difference in these gifs:

• 25.4.0
• 26.0.0 (+)

When scrolling, you will see a strange bounce of a collapsing toolbar.

See the layout code snippet below:

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <android.support.design.widget.AppBarLayout
        android:id="@+id/appBar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="@color/white_opacity10"
        android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar">

        <android.support.design.widget.CollapsingToolbarLayout
            android:id="@+id/collapsing"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:contentScrim="?attr/colorPrimary"
            app:layout_scrollFlags="scroll|exitUntilCollapsed|snap"
            app:scrimAnimationDuration="@integer/scrim_animation_short"
            app:titleEnabled="false">

            <FrameLayout
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_gravity="center"
                app:layout_collapseMode="parallax">

                <!-- Here is layout of header -->

            </FrameLayout>

            <android.support.v7.widget.Toolbar
                android:id="@+id/toolbar"
                android:layout_width="match_parent"
                android:layout_height="?attr/actionBarSize"
                android:layout_gravity="top"
                android:layout_marginBottom="?attr/actionBarSize"
                app:layout_collapseMode="pin"/>

            <android.support.design.widget.TabLayout
                android:id="@+id/tabLayout"
                android:layout_width="match_parent"
                android:layout_height="?attr/actionBarSize"
                android:layout_gravity="bottom"
                app:tabGravity="center"
                app:tabMode="scrollable"
                app:tabSelectedTextColor="@color/white"
                app:tabTextColor="@color/white_inactive"/>

        </android.support.design.widget.CollapsingToolbarLayout>

    </android.support.design.widget.AppBarLayout>

    <FrameLayout
        android:id="@+id/content"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_behavior="@string/appbar_scrolling_view_behavior">

        <android.support.v4.view.ViewPager
            android:id="@+id/viewPager"
            android:layout_width="match_parent"
            android:layout_height="match_parent"/>

    </FrameLayout>

</android.support.design.widget.CoordinatorLayout>

Does anyone have the same problem? Is this lib support error, or am I something wrong?

EDIT:

• a crash occurs only when you tap the screen, not when dragging
• for testing, you can pull out the following project: https://github.com/aaronbond/CollapsingToolbarLayoutExample and extend support for libs to 26 and above

Answer 1

- , AppBarLayout.

    <android.support.design.widget.AppBarLayout
        android:id="@+id/main_appbar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="@color/white_40"
        android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar" 
        app:layout_behavior="CustomFlingBehavior">

        <android.support.design.widget.CollapsingToolbarLayout
            android:id="@+id/main_collapsing"
            android:layout_width="match_parent"
            android:layout_height="144dp"
            app:layout_scrollFlags="scroll|exitUntilCollapsed">

            <LinearLayout
                android:id="@+id/ll_horizontal_ruler"
                android:layout_width="match_parent"
                android:layout_height="1dp"
                android:layout_gravity="bottom"
                android:orientation="horizontal"/>

        </android.support.design.widget.CollapsingToolbarLayout>
    </android.support.design.widget.AppBarLayout>

public final class FlingBehavior extends AppBarLayout.Behavior {

private static final int TOP_CHILD_FLING_THRESHOLD = 3;
private boolean isPositive;
private boolean enabled = true;

public FlingBehavior() {
    setDragCallback();
}

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

private void setDragCallback() {
    setDragCallback(new DragCallback() {
        @Override
        public boolean canDrag(@NonNull AppBarLayout appBarLayout) {
            return enabled;
        }
    });
}

@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;
}

public void setEnabled(boolean enabled) {
    this.enabled = enabled;
}

@Override
public boolean onStartNestedScroll(CoordinatorLayout parent, AppBarLayout child, View directTargetChild, View target, int nestedScrollAxes) {
    return enabled && super.onStartNestedScroll(parent, child, directTargetChild, target, nestedScrollAxes);
}

public boolean isEnabled() {
    return enabled;
}
}

: fooobar.com/questions/39420/...