xcode 约束不断更新不适用于 iOS 8
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Constraint constant update not work on iOS 8
提问by arthankamal
I have a strange problem with my constraints on this simple UIViewController. I have only two elements in it and precisely:
我对这个简单的 UIViewController 的约束有一个奇怪的问题。我只有两个元素，准确地说：
1 UIButton with these constraints:
1 PageControl with these constraints:
The problem is in iOS 8. I have connected the BottomSpace Constraint of UIPageControl to change the constant value (that in iOS 7 works perfectly). In iOS 8 the value doesn't change without any error. My code is simple:
1 个带有这些约束的 UIButton：
1 个带有这些约束的 PageControl：
问题出在 iOS 8 中。我已经连接了 UIPageControl 的底部空间约束来更改常量值（在 iOS 7 中完美运行）。在 iOS 8 中，该值不会在没有任何错误的情况下更改。我的代码很简单：
pageControlBottomConstraint.constant = 50
What is the difference between the two iOS version?
两个iOS版本有什么区别？
回答by arthankamal
Do the following,
请执行下列操作，
1. call updateConstraintsIfNeeded
2. call layoutIfNeeded (for currentView and ViewYouWantToUpdate)
1. 调用 updateConstraintsIfNeeded
2. 调用 layoutIfNeeded（用于 currentView 和 ViewYouWantToUpdate）
So you code should be
所以你的代码应该是
[pageControl updateConstraintsIfNeeded];
[self.view layoutIfNeeded];
[pageControl layoutIfNeeded];
if you want to animate the Constraints
如果你想动画 Constraints
Objective-C
目标-C
[pageControl updateConstraintsIfNeeded];
[UIView animateWithDuration:.75f animations:^{
__weak __typeof__(self) weakSelf = self
[self.view layoutIfNeeded];
[pageControl layoutIfNeeded];
}
Swift 3.0:
斯威夫特 3.0：
pageControl.updateConstraintsIfNeeded()
UIView.animate(withDuration: 0.75) {
weak var weakSelf = self
weakSelf?.view.layoutIfNeeded()
weakSelf?.pageControl.layoutIfNeeded()
}
