自支持lib 26.0.0起，折叠工具栏会出现小故障

Question

Since update of Android Support libs from version 25.4.0 to 26.0.0 (up to 27.0.0) I'm experiencing some weird behaviour in Collapsing Toolbar inside activity.

See difference on these gifs:

• 25.4.0
• 26.0.0 (+)

When scrolling up you will see strange bounce of collapsing toolbar.

See code snippet of layout bellow:

<?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>

Anybody experiencing same issue? Is this support lib bug, or me doing something wrong?

EDIT:

• glitch happens only when you fling screen, not when drag
• for testingyou can pull following project: https://github.com/aaronbond/CollapsingToolbarLayoutExample and encrease support libs to 26 and higher

Answer 1

I experienced something similar, and solved it by defining a custom behaviour for the 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>

and

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;
}
}

which is based upon the answer here: https://stackoverflow.com/a/40091360/494179