在 Swift 中枚举视图的 NSLayoutConstraints? [英] Enumerating a view's NSLayoutConstraints in Swift?

问题描述

   [self.view.constraints enumerateObjectsUsingBlock:^(NSLayoutConstraint *constraint, NSUInteger idx, BOOL *stop) {
        if ((constraint.firstItem == view) && (constraint.firstAttribute == NSLayoutAttributeTop)) {
            constraint.constant = -200;
        }
    }];

在 Objective-C 中，我将能够枚举视图的约束并相应地调整约束，但在 Swift 中我很难弄清楚如何去做.

In Objective-C, I would be able to enumerate a view's constraints and adjust the constraints accordingly, but in Swift I'm having difficulty figuring out to do the equivalent.

这是我在 swift 中应用代码的尝试:

here is my attempt at applying the code in swift:

   for (index, value) in enumerate(view.constraints()) {
        var constraint = value as NSLayoutConstraint
        if value.firstItem? = view  {
            constraint.constant = -200;
        }

    }

我收到一个编译器错误，指出类型 '[AnyObject!'不符合此代码第一行的协议序列".

I get a compiler error stating "Type '[AnyObject!' does not conform to protocol 'Sequence' on the first line of this code.

任何帮助将不胜感激！

推荐答案

As constraints() 返回 [AnyObject]! 这是可选的所以你需要解开 view.constraints()! 在使用之前.所以解开它使用下面的代码

As constraints() returns [AnyObject]! which is optional so you need to unwrap view.constraints()! before use.So unwrap it Use below code

    for (index, value) in enumerate(view.constraints()!) {
        var constraint = value as NSLayoutConstraint
        if value.firstItem? = view  {
            constraint.constant = -200;
        }

    }

你也不能分配 firstItem 因为它是只读属性.我想你想比较它.所以使用 if value.firstItem！作为 UIView == self.view. 所以使用 `

Also you cannot assign firstItem as it is readonly property.I think you want to compare it.So use if value.firstItem! as UIView == self.view.So use `

 for (index, value) in enumerate(view.constraints()!) {
        var constraint = value as NSLayoutConstraint
        if value.firstItem! as UIView == self.view {
            constraint.constant = -200;
        }

    }

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