ios - UIImageView 重复显示在另一个单元格中

Question

我在表格单元格中的 UIView 中动态添加了一个 UIImageView(作为缩略图)及其 NSLayoutConstraints。我有两个问题。

1. 添加 ImageView 后，如果用户向该表中插入文本，仍会显示图像。我的意思是，而不是文本表打印一张图片。但是，如果我停止并重新运行该应用程序，这次文本会按应有的方式显示。不过，如果我写一个文字图片来了。为什么以及我应该做什么？

2. 我这样设置图像及其约束:

   -(void)setThumbnail:(UIImageView)imageView {
   
   [self.messageView addSubview:imageView];
   
   NSLayoutConstraint *leadingOfThumbnail = [NSLayoutConstraint constraintWithItem:imageView attribute:NSLayoutAttributeLeading relatedBy:NSLayoutRelationEqual toItem:self.messageView attribute:NSLayoutAttributeLeading multiplier:1.0 constant:8.f];
   NSLayoutConstraint *trailingOfThumbnail = [NSLayoutConstraint constraintWithItem:imageView attribute:NSLayoutAttributeTrailing relatedBy:NSLayoutRelationEqual toItem:self.messageView attribute:NSLayoutAttributeTrailing multiplier:1.0 constant:-8.f];
   NSLayoutConstraint *topOfThumbnail = [NSLayoutConstraint constraintWithItem:imageView attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual toItem:self.messageView attribute:NSLayoutAttributeTop multiplier:1.0 constant:8.f];
   NSLayoutConstraint *bottomOfThumbnail = [NSLayoutConstraint constraintWithItem:imageView attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual toItem:self.messageView attribute:NSLayoutAttributeBottom multiplier:1.0 constant:-8.f];
   [self.messageView addConstraint:leadingOfThumbnail];
   [self.messageView addConstraint:trailingOfThumbnail];
   [self.messageView addConstraint:topOfThumbnail];
   [self.messageView addConstraint:bottomOfThumbnail];
   [self.messageView setTranslatesAutoresizingMaskIntoConstraints:NO];
   
   [self.messageView removeConstraints:[self.messageTextLabel constraints]];
   }
   

加载时，出现约束错误。它说:

2016-10-07 09:35:32.532 application[3733:2922397] 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)  (
    "NSAutoresizingMaskLayoutConstraint:0x1281474d0 h=--& v=--& UIImageView:0x126d7e020.midY == + 100",
    "NSAutoresizingMaskLayoutConstraint:0x128147520 h=--& v=--& V:[UIImageView:0x126d7e020(200)]",
    "NSLayoutConstraint:0x126d6c880 V:|-(8)-[UIImageView:0x126d7e020]   (Names: '|':UIView:0x1281480d0 )" )

Will attempt to recover by breaking constraint  NSLayoutConstraint:0x126d6c880 V:|-(8)-[UIImageView:0x126d7e020]   (Names: '|':UIView:0x1281480d0 )

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.

我检查过，我设置的前导和顶部约束导致了这个错误。他们已经不能正常工作了。我的图片是200 * 200，所以不需要高宽限制。我只想要 8 pt leading, trailing, top, bottom 从消息 View 。有什么问题？

谢谢。

第一个问题的解释编辑: 表格随机放置 UIImageView，多个单元格 - 不是它应该的样子。

Answer 1

您可能想要实现 prepareForReuse 方法并在那里做一些清理，将 imageView 设置为 nil 并将其从此处的 subview 中删除。
当您的单元格出列并即将在 tableview 中重复使用时，将调用此方法。