swift 3:如何在UIView上对齐(垂直和水平)UIButton？

Question

我正在尝试创建一个图像UIButton,并使用Interface Builder以编程方式设置其位置.原因是我将根据ViewController中的一些逻辑显示/隐藏按钮.然而,我花了过去~4小时搜索无济于事.我尝试了以下方法:

1. 约束:看似推荐的方法
2. 将UIButton.center属性设置为 CGPoint(x: self.view.frame.width / 2, y: self.view.frame.height / 2)

这是完整的代码:

    class ViewController: UIViewController{
    //this is here so i can access playButton across different functions that i'll define in this ViewController
    let playButton:UIButton = {
      let play_btn = UIButton()
        play_btn.setImage(UIImage(named:"my_button_image.png"), for: UIControlState.normal)
        play_btn.translatesAutoresizingMaskIntoConstraints = false
        return play_btn
    }()

    override func viewDidLoad() {

       super.viewDidLoad()


       playButton.addTarget(self, action:#selector(self.toggle), for: .touchDown)
       let centerX = NSLayoutConstraint(item: self.playButton, attribute: NSLayoutAttribute.centerX, relatedBy: NSLayoutRelation.equal, toItem: self.view, attribute: NSLayoutAttribute.centerX, multiplier: 1, constant: 0)
       let centerY = NSLayoutConstraint(item: self.playButton, attribute: NSLayoutAttribute.centerY, relatedBy: NSLayoutRelation.equal, toItem: self.view, attribute: NSLayoutAttribute.centerY, multiplier: 1, constant: 0)

       self.view.addConstraints([centerX, centerY])

       view.addSubview(playButton)

    }
}

我也尝试过: playButton.center = CGPoint(x: self.view.frame.width / 2, y: self.view.frame.height / 2)

以及:

playButton.center.x = self.view.center.x playButton.center.y = self.view.center.y

以上都不起作用:(

任何帮助/建议/建议非常感谢!

Answer 1

当我尝试你的代码时,它崩溃了.问题是你在初始化视图之前尝试添加约束,添加约束应该在viewWillLayoutSubviews()中

在任何情况下,我建议创建更简单的按钮,即使按钮居中视图

let btn = UIButton(frame: CGRect(x:0 , y:0, width:100, heigth: 60))
btn.center = self.view.center
self.view.addSubview(btn)

以上将自动将按钮限制在视图的中心

希望能帮助到你!