ios 以编程方式更改高度约束
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Change height constraint programmatically
提问by mxch
I want to change the height constraint of a UITextView programmatically so I set the constraint as an outlet in my controller like this:
我想以编程方式更改 UITextView 的高度约束，因此我将约束设置为控制器中的出口，如下所示：
@property (strong, nonatomic) IBOutlet NSLayoutConstraint *descriptionHeightConstraint;
To change it I do the following:
要更改它，我执行以下操作：
self.descriptionHeightConstraint.constant = self.description.contentSize.height;
This works if I do it in viewDidAppearbut the problem with this is that I can see how the height changes after the view displayed which is not very user friendly so I tried doing it in viewWillAppearbut didn't work there, the height doesn't change. Calling setNeedsUpdateConstraintsafter changing the constraint didn't work either.
如果我在viewDidAppear 中这样做，这会起作用，但问题在于我可以看到显示视图后高度如何变化，这对用户来说不是很友好，所以我尝试在viewWillAppear 中这样做，但没有在那里工作，高度没有改变。在更改约束后调用setNeedsUpdateConstraints也不起作用。
Why is working in viewDidAppear and not in viewWillAppear? Any workaround?
为什么在 viewDidAppear 中工作而不是在 viewWillAppear 中工作？任何解决方法？
Thanks in advance!
提前致谢！
采纳答案by bilobatum
Try setting the constant in viewDidLayoutSubviewsinstead.
尝试设置常量viewDidLayoutSubviews。
Note that using the text view's contentSizeproperty to set the text view's height does not work in iOS 7. See https://stackoverflow.com/a/18837714/1239263
请注意，使用文本视图的contentSize属性设置文本视图的高度在 iOS 7 中不起作用。请参阅https://stackoverflow.com/a/18837714/1239263
