ios - 约束会影响哪些属性？

Question

我正在尝试理解约束的逻辑，但有些事情我无法找到...

我创建了一个自定义 UIButton 并添加了一些约束来更改它的宽度和高度，并且它工作正常。但是我找不到按钮的新宽度和高度值。约束更改后如何获取这些值？

这是我的代码...

import Foundation
import UIKit

class RoundedButton: UIButton {

    class func make (text:String, color:UIColor) -> RoundedButton {

        let button = self.buttonWithType(UIButtonType.System) as RoundedButton
        button.frame = CGRectMake(0, 0, 150, 40)
        button.layer.cornerRadius = 20
        button.layer.borderColor = color.CGColor
        button.layer.borderWidth = 2

        button.setTitle(text, forState: UIControlState.Normal)
        button.setTitleColor(color, forState: UIControlState.Normal)
        button.titleLabel?.font = UIFont(name: "OpenSans-Semibold", size: 14)
        return button
    }

    func resizeAndPlace(width:CGFloat, height:CGFloat)
    {
        self.setTranslatesAutoresizingMaskIntoConstraints(false)

        let widthCons = NSLayoutConstraint(item: self, attribute: NSLayoutAttribute.Width, relatedBy: NSLayoutRelation.Equal, toItem: nil, attribute: NSLayoutAttribute.NotAnAttribute, multiplier: 1, constant: width)

        let heightCons = NSLayoutConstraint(item: self, attribute: NSLayoutAttribute.Height, relatedBy: NSLayoutRelation.Equal, toItem: nil, attribute: NSLayoutAttribute.NotAnAttribute, multiplier: 1, constant: height)

        self.superview!.addConstraint(widthCons)
        self.superview!.addConstraint(heightCons)

        println(self.frame.width) // 150 and never changes
    }
}

Answer 1

您没有看到约束生效的原因是布局尚未发生。如果你打电话:

self.layoutIfNeeded()

设置约束后，值将立即反射(reflect)在框架中。