ios - Collection View 上奇怪的自动布局行为

Question

我遇到自动布局问题，控制台报告单元格中的 ImageView 存在问题:

RefreshCatalogue[31754:16177989] Unable to simultaneously satisfy constraints.
    Probably at least one of the constraints in the following list is one you don't want. Try this: (1) look at each constraint and try to figure out which you don't expect; (2) find the code that added the unwanted constraint or constraints and fix it. (Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints) 
(
    "<NSLayoutConstraint:0x7fa98103b740 V:[UIImageView:0x7fa9810375d0]-(0)-|   (Names: '|':UIView:0x7fa9810371d0 )>",
    "<NSLayoutConstraint:0x7fa98103b7e0 V:|-(0)-[UIImageView:0x7fa9810375d0]   (Names: '|':UIView:0x7fa9810371d0 )>",
    "<NSLayoutConstraint:0x7fa98103b8d0 UIImageView:0x7fa9810375d0.centerY == UIImageView:0x7fa981037490.centerY>",
    "<NSLayoutConstraint:0x7fa98103ba60 UIImageView:0x7fa981037490.top == UIView:0x7fa9810371d0.topMargin + 71>",
    "<NSAutoresizingMaskLayoutConstraint:0x7fa980d44a10 h=--& v=--& V:[UIView:0x7fa9810371d0(50)]>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x7fa98103b8d0 UIImageView:0x7fa9810375d0.centerY == UIImageView:0x7fa981037490.centerY>

Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful.

问题是如果我这样做:

[self.collectionView reloadItemsAtIndexPaths:@[indexPath]];

即使 ImageView 似乎具有正确的框架，也没有任何显示，图像属性已设置。如果我重新加载整个 Collection View :

[self.collectionView reloadData];

错误仍然存​​在，但图像显示。代码在这里公开，有兴趣的可以看看: https://github.com/Ridiculous-Innovations/RefreshCatalogue

此外， Storyboard中的所有约束似乎都是蓝色的。知道可能导致问题的原因吗？

编辑:不用说所有元素，包括 ImageView 都在正确的位置(我调试了帧并设置了随机颜色)但是图像直到刷新才显示...有时单元格不显示完全显示

Answer 1

您遇到 UIImageView:0x7fa981037490.top == UIView:0x7fa9810371d0.topMargin + 71 和高度为 0 的父框架的问题(因此 imageview 高度必须为负，但这是不允许的)，就像在调用 dequeueReusableCell 方法之后一样。这种情况下可能的解决方法是将嵌套 View 中最底部约束的优先级从 1000 更改为 999(垂直空间 - catalogueHeaderCell - ImageView 和垂直空间 - catalogueCell - 信息 View )。