iOS - 通过Swift更改约束的乘数 [英] iOS - Change the multiplier of constraint by Swift

问题描述

如何使用Swift更改约束的乘数。

How to change the multiplier of a constraint by using Swift.

someConstraint.multiplier = 0.6 // error: 'multiplier' is get-only property

我想知道如何更改代码中的乘数（Swift） 。

I would like to know how to change the multiplier in code (Swift).

推荐答案

由于乘数是一个只读属性，你可以要改变它，你需要用它修改过的克隆来替换约束。

Since multiplier is a read-only property and you can't change it, you need to replace the constraint with its modified clone.

你可以写一个扩展来做它，如：

You can write an extension to do it, like:

extension NSLayoutConstraint {
    func constraintWithMultiplier(_ multiplier: CGFloat) -> NSLayoutConstraint {
        return NSLayoutConstraint.constraintWithItem(self.firstItem, attribute: self.firstAttribute, relatedBy: self.relation, toItem: self.secondItem, attribute: self.secondAttribute, multiplier: multiplier, constant: self.constant)
    }
}

Swift 3.0+版本：

Swift 3.0+ version:

extension NSLayoutConstraint {
    func constraintWithMultiplier(_ multiplier: CGFloat) -> NSLayoutConstraint {
        return NSLayoutConstraint(item: self.firstItem, attribute: self.firstAttribute, relatedBy: self.relation, toItem: self.secondItem, attribute: self.secondAttribute, multiplier: multiplier, constant: self.constant)
    }
}

用法：

var newConstraint = self.constraintToChange.constraintWithMultiplier(0.75)
self.view!.removeConstraint(self.constraintToChange)
self.view!.addConstraint(self.constraintToChange = newConstraint)
self.view!.layoutIfNeeded()

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