ios – UIVisualEffectView模糊约束动画bug

我在扩展和签约UIEffectView时遇到问题.它的扩展很好,但是当它收缩时,它会立即捕捉到最后的高度并滑动到位,留下微弱的活力效果.想要一个gif来说明问题.
http://i.imgur.com/Lh8q7m1.gif

这种情况发生在一个新的空白项目设置中：

这是动画代码：

- (IBAction)toggleEffects:(id)sender {
[self.view setNeedsLayout];

if(self._effectsHeight.constant == 50){
    self._effectsHeight.constant = 500;
}else{
    self._effectsHeight.constant = 50;
}
[UIView animateWithDuration:1.5f
                 animations:^{
                     [self.view layoutIfNeeded];
                 }];

}

[UIView animateWithDuration:1.5f
                 animations:^{
                     if(self._effectsHeight.constant == 50){
                        self._effectsHeight.constant = 500;
                     }else{
                        self._effectsHeight.constant = 50;
                          }
                 }];