删除视图时约束会发生什么

问题描述

我的问题很简单，但我在文档中找不到任何信息.

The question I have is simple but I couldn't find any information in the documentation.

当视图从视图层次结构中移除(或移动到另一个视图)时，布局约束会发生什么情况?

What happens with layout constraints when a view is removed from the view hierarchy (or moved to another view)?

例如，让我们有容器 C 与子视图 A 和 B.容器 C 包含一些约束.然后我们调用 [A removeFromSuperview].A 的约束会发生什么?

For example, let's have container C with subviews A and B. Container C holds some constraints. Then we call [A removeFromSuperview]. What happens with the constraints for A?

如果我们再次将 A 添加到 C 会发生什么?

What then happens if we add A to C again?

推荐答案

约束被移除.如果再次添加 A，则必须为其创建新的约束，或者如果在删除 A 之前保存约束，则可以重新添加它们.当我做这样的事情时，我会为一个名为 view1 的视图保存这样的约束:

The constraints are removed. If you add A again, you will have to make new constraints for it, or if you save the constraints before you remove A, you can add them back. When I do something like this, I save the constraints like this for a view called view1:

self.portraitConstraints = [NSMutableArray new];
for (NSLayoutConstraint *con in self.view.constraints) {
    if (con.firstItem == self.view1 || con.secondItem == self.view1) {
       [self.portraitConstraints addObject:con];
    }
}

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