/** Call when the ViewGroup is layout. */
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
super.onLayout(changed, l, t, r, b);
int galleryCenter = getCenterOfGallery();
View v = this.getChildAt(0);
int height = (null != v) ? v.getMeasuredHeight() : 50;
int top = galleryCenter - height / 2;
int bottom = top + height;
mSelectorBound.set(getPaddingLeft(), top, getWidth() - getPaddingRight(), bottom);
}
