问检测浮动操作按钮何时隐藏

EN

public interface OnAppearanceChangedListener {
    void onAppearanceChanged(int alpha);
}

public class MyFloatingActionButton extends FloatingActionButton {
    private OnAppearanceChangedListener mListener;

    public void setListener(OnAppearanceChangedListener mListener){
        this.mListener = mListener;
    }
    /*insert code here to call mListener.onAppearanceChanged(),
      probably by overriding some method */
}

public class MainActivity extends Activity implements OnAppearanceChangedListener {
    @Override
    public void onAppearanceChanged(boolean visible) {
        // I want this function to be called when Floating Action Button hide/show state is changed
    }
}