iOS NSLayoutConstraint使用constraintWithItem修复宽度 [英] iOS NSLayoutConstraint Fixed Width using constraintWithItem

问题描述

我想设置一个约束，以编程方式为UIButton提供固定（常量）宽度。我知道我可以使用constraintsWithVisualFormat来做到这一点，但我一直在使用constraintWithItem来解决代码中的所有约束。如果有任何方法可以使用constraintWithItem，我想知道好奇/一致性。

I'd like to set a constraint to give a UIButton a fixed (constant) width programmatically. I know I can do this with constraintsWithVisualFormat, but I've been using constraintWithItem for all of my constraints in code. I was wondering for the sake of curiosity/consistency if there was any way to do this with constraintWithItem.

推荐答案

找到我的解决方案。只需将另一个对象设置为nil，将另一个属性设置为NSLayoutAttributeNotAnAttribute（这是我没想到的）并使用常量参数作为固定宽度：

Found my solution. Just set the other object to nil, and the other attribute to NSLayoutAttributeNotAnAttribute (this was what I failed to think of) and use the constant parameter for the fixed width:

[self addConstraint:[NSLayoutConstraint constraintWithItem:myButton
      attribute:NSLayoutAttributeWidth 
      relatedBy:NSLayoutRelationEqual 
      toItem:nil 
      attribute:NSLayoutAttributeNotAnAttribute 
      multiplier:1.0 
      constant:200]];

编辑：因为这个答案似乎仍然得到了相当多的观点，我想我会添加Swift语法：

since this answer still seems to get a fair share of views, I thought I'd add the Swift syntax:

self.addConstraint(NSLayoutConstraint(
        item: myButton,
        attribute: .width,
        relatedBy: .equal,
        toItem: nil,
        attribute: .notAnAttribute,
        multiplier: 1.0,
        constant: 200))

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