AppBarLayout 부드럽게 스크롤

어느 양키성님께서 만든 클래스

아주 부드럽게 작동한다

/**
 * Created by achee7059 on 2017. 4. 14..
 *
 * 앱바 스크롤 부드럽게 하는 클래스
 */

public class FlingBehavior extends AppBarLayout.Behavior {

    private static final String TAG = FlingBehavior.class.getName();
    private static final int TOP_CHILD_FLING_THRESHOLD = 1;
    private static final float OPTIMAL_FLING_VELOCITY = 3500;
    private static final float MIN_FLING_VELOCITY = 20;

    boolean shouldFling = false;
    float flingVelocityY = 0;

    public FlingBehavior() {
    }

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

    @Override
    public void onNestedPreScroll(CoordinatorLayout coordinatorLayout, AppBarLayout child, View target,
                                  int velocityX, int velocityY, int[] consumed) {

        super.onNestedPreScroll(coordinatorLayout, child, target, velocityX, velocityY, consumed);

        if (velocityY > MIN_FLING_VELOCITY) {
            shouldFling = true;
            flingVelocityY = velocityY;
        } else {
            shouldFling = false;
        }
    }

    @Override
    public void onStopNestedScroll(CoordinatorLayout coordinatorLayout, AppBarLayout abl, View target) {
        super.onStopNestedScroll(coordinatorLayout, abl, target);
        if (shouldFling) {
            Log.d(TAG, "onNestedPreScroll: running nested fling, velocityY is " + flingVelocityY);
            onNestedFling(coordinatorLayout, abl, target, 0, flingVelocityY, true);
        }
    }

    @Override
    public boolean onNestedFling(CoordinatorLayout coordinatorLayout, AppBarLayout child, View target,
                                 float velocityX, float velocityY, boolean consumed) {

        if (target instanceof RecyclerView && velocityY < 0) {
            Log.d(TAG, "onNestedFling: target is recyclerView");
            final RecyclerView recyclerView = (RecyclerView) target;
            final View firstChild = recyclerView.getChildAt(0);
            final int childAdapterPosition = recyclerView.getChildAdapterPosition(firstChild);
            consumed = childAdapterPosition > TOP_CHILD_FLING_THRESHOLD;
        }

        // prevent fling flickering when going up
        if (target instanceof NestedScrollView && velocityY > 0) {
            consumed = true;
        }

        if (Math.abs(velocityY) < OPTIMAL_FLING_VELOCITY) {
            velocityY = OPTIMAL_FLING_VELOCITY * (velocityY < 0 ? -1 : 1);
        }
        Log.d(TAG, "onNestedFling: velocityY - " + velocityY + ", consumed - " + consumed);

        return super.onNestedFling(coordinatorLayout, child, target, velocityX, velocityY, consumed);
    }
}

<android.support.design.widget.AppBarLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:id="@+id/abl_recommend_detail"
    app:layout_behavior="com.ubist.tourtainment.flag.utils.FlingBehavior">

mNestedScrollView.setOnScrollChangeListener(new NestedScrollView.OnScrollChangeListener() {
    @Override
    public void onScrollChange(NestedScrollView v, int scrollX, int scrollY, int oldScrollX, int oldScrollY) {
        if (!shouldScroll)
            mNestedScrollView.fullScroll(ScrollView.FOCUS_UP);
    }
});

@Override
public void onOffsetChanged(AppBarLayout appBarLayout, int verticalOffset) {

    Log.e(TAG, "verticalOffset = " + Math.abs(verticalOffset));
    Log.e(TAG, "appBarLayout.getTotalScrollRange = " + appBarLayout.getTotalScrollRange());

    shouldScroll = Math.abs(verticalOffset) == appBarLayout.getTotalScrollRange();

}