集合视图上的奇怪自动布局行为

Question

我有自动布局的问题,控制台报告我在单元格中的图像视图的问题:

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]];

即使图像视图似乎具有正确的帧也没有显示,图像属性被设置.如果我重新加载整个集合视图:

[self.collectionView reloadData];

错误仍然存​​在,但图像显示.这里的代码是开放的,任何人都有兴趣看看:https: //github.com/Ridiculous-Innovations/RefreshCatalogue

此外,故事板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,包括图像视图都在正确的位置(我做了调试帧和设置随机颜色)但图像直到刷新才显示...有时单元格根本不显示

Answer 1

您遇到 UIImageView:0x7fa981037490.top == UIView:0x7fa9810371d0.topMargin + 71 和父框架高度为 0 的问题（因此 imageview 高度必须为负数，但这是不允许的），就像调用 dequeueReusableCell 方法之后一样。这种情况的可能解决方法是将嵌套视图中最底部约束的优先级从 1000 更改为 999（垂直空间 - CatalogueHeaderCell - 图像视图和垂直空间 - CatalogueCell - 信息视图）。