ios - 当 AlertController 出现时，UICollectionViewFlowLayout 错误

Question

我想在 super ViewController 中呈现一个 AlertController。 (事实上​​，里面没有CollectionView)，但是当AlertController出现时。调试区会调用一些bug:

//2016-02-25 14:55:06.721 treatα[53173:1063624] the behavior of the 
UICollectionViewFlowLayout is not defined because:
//2016-02-25 14:55:06.721 treatα[53173:1063624] the item height must 
be less than the height of the UICollectionView minus the section 
insets top and bottom values, minus the content insets top and 
bottom values.
//2016-02-25 14:55:06.722 treatα[53173:1063624] The relevant UICollectionViewFlowLayout instance is
 <_UIAlertControllerCollectionViewFlowLayout: 0x7fc883dfb1d0>, and it is attached to <UICollectionView: 0x7fc8848de800; 
frame = (0 104.667; 270 44); clipsToBounds = YES; gestureRecognizers = <NSArray: 0x7fc883dfbb50>; layer = <CALayer: 0x7fc883dfb680>; contentOffset: {0, 0}; 
contentSize: {0, 0}> collection view layout: <_UIAlertControllerCollectionViewFlowLayout: 0x7fc883dfb1d0>.
//2016-02-25 14:55:06.722 treatα[53173:1063624] Make a symbolic breakpoint at UICollectionViewFlowLayoutBreakForInvalidSizes
             to catch this in the debugger.

Answer 1

我自己解决了。需要添加

alert.view.setNeedsLayout()

之前

self.presentViewController(alert, animated: true, completion: nil)

然后，修复bug