setOnScrollChangeListener未按预期工作

Question

为什么setsetOnScrollChangeListener不起作用。我已将nestedscrollview定义为。有时它确实有效，但大部分时间即使没有任何代码更改也无法正常工作。

 <android.support.v4.widget.NestedScrollView
        android:id="@+id/lvToDoList"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:fillViewport="true"
        app:layout_behavior="@string/appbar_scrolling_view_behavior">
</android.support.v4.widget.NestedScrollView>




 scrollView.setOnScrollChangeListener(new NestedScrollView.OnScrollChangeListener() {
                @Override
                public void onScrollChange(NestedScrollView v, int scrollX, int scrollY, int oldScrollX, int oldScrollY) {

                    Log.v("scrollx ",Integer.toString(scrollX));
                    Log.v("scrollY ",Integer.toString(scrollY));
                    Log.v("oldScrollX ",Integer.toString(oldScrollX));
                    Log.v("oldScrollY ",Integer.toString(oldScrollY));

                    if (scrollY>oldScrollY)
                        fabBG1.hide();
                    else
                        fabBG1.show();

                }
            });

任何提示？