@Override
    public void onNestedScrollAccepted(View child, View target, int nestedScrollAxes) {
        mParentHelper.onNestedScrollAccepted(child, target, nestedScrollAxes);
        startNestedScroll(ViewCompat.SCROLL_AXIS_VERTICAL);
    }
Sentinel value for no current active pointer.
Used by {@link #mActivePointerId}.
app/src/main/java/home/smart/fly/animations/widget/NestedScrollView.java