我正在使用 iMessage 应用程序并以编程方式添加了一个 View 。但是，我似乎无法找出正确的约束条件来使其始终保持正确的大小。例如，如果我离开另一个扩展名并返回到它， View 将向下移动几百像素。我认为这与 .isActive 有关。我的目标是让 View 自动调整大小以始终保持正确的大小或占据全部可用的高度和宽度。

func createBrowser() {
    let controller = MSStickerBrowserViewController(stickerSize: .small)
    addChildViewController(controller)
    view.addSubview(controller.view)

    controller.view.translatesAutoresizingMaskIntoConstraints = false
    controller.stickerBrowserView.backgroundColor = UIColor.blue
    controller.stickerBrowserView.dataSource = self

    view.topAnchor.constraint(equalTo: controller.view.topAnchor).isActive = true
    view.bottomAnchor.constraint(equalTo: controller.view.bottomAnchor).isActive = true
    view.leftAnchor.constraint(equalTo: controller.view.leftAnchor).isActive = true
    view.rightAnchor.constraint(equalTo: controller.view.rightAnchor).isActive = true
    view.centerXAnchor.constraint(equalTo: controller.view.centerXAnchor).isActive = true
    view.centerYAnchor.constraint(equalTo: controller.view.centerYAnchor).isActive = true
}

截图:https://d17oy1vhnax1f7.cloudfront.net/items/1F2B0s3v0s1k3E2L0Z07/Screen%20Shot%202016-09-19%20at%2011.42.51%20AM.png

最佳答案

为了更好地解释我整理了以下内容。这演示了两种固定 subview 布局的方法。使用约束时，我更喜欢将约束创建为数组并一次性激活它们，正如您将在 createredSquareWithConstraints 的代码中看到的那样。约束只是一个将一个 View 的特征与另一个 View 的特征相关联的线性方程。例如，在“伪代码”中，我的数组中的第一个约束可以写成:

“将 subview 的前导边距设置为容器 View 前导边距的 1 倍加上常数 0。”

(这就是我之前感到困惑的原因，因为在我看来，您好像是在根据其中一个 subview 的特征设置包含 View 的约束。)

虽然使用布局约束仍然完全有效，但我认为现在首选的方法是覆盖 viewWillTransitionToSize() 委托(delegate)方法，它只要求您在给定包含 View 的大小的情况下指定 View 的框架是什么 View Controller 的 subview 应该是。因此，我也包含了一个实现，创建一个带有初始框架的黄色方 block ，然后在调用 viewWillTransitionToSize 时修改该框架。我个人觉得这比使用布局约束要简单得多。

如果您使用按钮并旋转屏幕，您应该会发现这两种方法都可以实现相同的效果。 [注意，我将一个正方形标记为受约束，另一个标记为不受约束，但实际上它们当然都受到约束，只是方式不同。我要补充一点，这显然不是您在实践中做事的方式 - 您应该选择一种方法并坚持使用它，否则您的代码将到处都是!]。

希望对您有所帮助!

import UIKit

class ViewController: UIViewController {

    var constrainedredSquare : UIView!
    var unconstrainedRedSquare : UIView!
    var methodOneButton : UIButton!
    var methodTwoButton : UIButton!

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        self.view.backgroundColor = UIColor.blue

        func getButton(name: String) -> UIButton {
            let button : UIButton = UIButton()
            button.backgroundColor = UIColor.white
            button.layer.cornerRadius = 3
            button.clipsToBounds = true
            button.setTitle(name, for: UIControlState.normal)
            button.setTitleColor(UIColor.black, for: UIControlState.normal)
            return button
        }

        self.methodOneButton = getButton(name: "Red - Constraints")
        self.methodTwoButton = getButton(name: "Yellow - viewWillTransitionToSize")

        self.methodOneButton.addTarget(self, action: #selector(self.createRedSquareWithConstraints), for: .touchUpInside)
        self.methodTwoButton.addTarget(self, action: #selector(self.createYellowSquareWithoutConstraints), for: .touchUpInside)
        self.methodOneButton.frame = CGRect(origin: CGPoint(x: 200, y: 100), size: CGSize(width: 300, height: 300))
        self.methodTwoButton.frame = CGRect(origin: CGPoint(x: self.view.frame.width - 500, y: 100), size: CGSize(width: 300, height: 300))
        self.view.addSubview(self.methodOneButton)
        self.view.addSubview(self.methodTwoButton)

    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    override func viewWillTransition(to size: CGSize, with coordinator: UIViewControllerTransitionCoordinator) {
        if let _ = self.unconstrainedRedSquare {
            self.unconstrainedRedSquare.frame = CGRect(origin: CGPoint.zero, size: size)
        }
        self.methodOneButton.frame = CGRect(origin: CGPoint(x: 200, y: 100), size: CGSize(width: 300, height: 300))
        self.methodTwoButton.frame = CGRect(origin: CGPoint(x: size.width - 500, y: 100), size: CGSize(width: 300, height: 300))
    }


    func createYellowSquareWithoutConstraints() {
        if let _ = self.unconstrainedRedSquare {
            self.unconstrainedRedSquare.removeFromSuperview()
        }
        else
        {
            if let _ = constrainedredSquare {
                self.constrainedredSquare.removeFromSuperview()
            }
            self.unconstrainedRedSquare = UIView()
            self.unconstrainedRedSquare.backgroundColor = UIColor.yellow
            self.unconstrainedRedSquare.frame = CGRect(origin: CGPoint.zero, size: self.view.frame.size)
            self.view.addSubview(self.unconstrainedRedSquare)

            self.view.bringSubview(toFront: self.methodOneButton)
            self.view.bringSubview(toFront: self.methodTwoButton)
        }

    }

    func createRedSquareWithConstraints() {
        if let _ = self.constrainedredSquare {
            self.constrainedredSquare.removeFromSuperview()
        }
        else
        {
            if let _ = self.unconstrainedRedSquare {
                self.unconstrainedRedSquare.removeFromSuperview()
            }
            let redSquare : UIView = UIView()
            redSquare.backgroundColor = UIColor.red

            self.view.addSubview(redSquare)

            self.view.bringSubview(toFront: self.methodOneButton)
            self.view.bringSubview(toFront: self.methodTwoButton)

            let rsConstraints : [NSLayoutConstraint] = [NSLayoutConstraint(item: redSquare, attribute: NSLayoutAttribute.leading, relatedBy: NSLayoutRelation.equal, toItem: self.view, attribute: NSLayoutAttribute.leading, multiplier: 1.0, constant: 0),
                                                 NSLayoutConstraint(item: redSquare, attribute: NSLayoutAttribute.trailing, relatedBy: NSLayoutRelation.equal, toItem: self.view, attribute: NSLayoutAttribute.trailing, multiplier: 1.0, constant: 0),
                                                 NSLayoutConstraint(item: redSquare, attribute: NSLayoutAttribute.top, relatedBy: NSLayoutRelation.equal, toItem: self.view, attribute: NSLayoutAttribute.top, multiplier: 1.0, constant: 0),
                                                 NSLayoutConstraint(item: redSquare, attribute: NSLayoutAttribute.bottom, relatedBy: NSLayoutRelation.equal, toItem: self.view, attribute: NSLayoutAttribute.bottom, multiplier: 1.0, constant: 0),
                                                 NSLayoutConstraint(item: redSquare, attribute: NSLayoutAttribute.width, relatedBy: NSLayoutRelation.equal, toItem: self.view, attribute: NSLayoutAttribute.width, multiplier: 1.0, constant: 0),
                                                 NSLayoutConstraint(item: redSquare, attribute: NSLayoutAttribute.height, relatedBy: NSLayoutRelation.equal, toItem: self.view, attribute: NSLayoutAttribute.height, multiplier: 1.0, constant: 0)]
            redSquare.translatesAutoresizingMaskIntoConstraints = false
            NSLayoutConstraint.activate(rsConstraints)
        }
    }
}

关于ios - 以编程方式快速添加全尺寸 View ，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/39577079/