ios 在 Swift 中以编程方式更新约束的常量属性？
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Update the constant property of a constraint programmatically in Swift?
提问by Cesare
I want to animate an object, so I declare a constraint and add it to the view. I then update the constantproperty of the constraint inside an UIViewanimation. Why doesn't this code move the object?
我想为一个对象设置动画，所以我声明了一个约束并将其添加到视图中。然后我更新动画中constant约束的属性UIView。为什么这段代码不移动对象？
UIView.animateWithDuration(1, animations: {
myConstraint.constant = 0
self.view.updateConstraints(myConstraint)
})
回答by duan
In order to declare an animation, you cannot re-define the constraint and call updateConstraints. You are supposed to change the constantof your constraint and follow the format below:
为了声明动画，您不能重新定义约束并调用updateConstraints. 您应该更改constant约束并遵循以下格式：
self.view.layoutIfNeeded()
UIView.animate(withDuration: 1) {
self.sampleConstraint.constant = 20
self.view.layoutIfNeeded()
}
