当容器视图控制器动态更改子视图控制器时，布局不起作用

Question

我有一个包含contavewiewController的MainViewController。

单击ChildViewControllera中的按钮时，ContainServiewController开始显示ChildViewControllera，并将其动态切换到ChildViewControllerb：

func showNextViewContoller() {

    let childViewControllerB = ChildViewControllerB()

    container.addViewController(childViewControllerB)
    container.children.first?.remove()  // Remove childViewControllerA
}

<

a a href =“ https://i.sstatic.net/zlimu.png” noreferrer“>

第二视图控制器（viewControllerb）具有图像视图，我会喜欢在中心展示。因此，我分配了以下约束：

imageView.translatesAutoresizingMaskIntoConstraints = false
imageView.contentMode = .scaleAspectFill
   
    NSLayoutConstraint.activate([
        imageView.centerYAnchor.constraint(equalTo: view.centerYAnchor),
        imageView.centerXAnchor.constraint(equalTo: view.centerXAnchor),
        imageView.heightAnchor.constraint(equalTo: view.heightAnchor, multiplier: 0.6),
    ])

我遇到的问题是图像视图不是垂直居中的：它比应有的要低。

当我运行该应用程序时，该应用程序contunerveiwcontroller首先显示ChildViewControllerb，然后按预期工作。此问题仅在ChildViewControllera之后动态切换时才发生：

为了帮助调试，我将以下代码添加到所有三个ViewControllers：

override func viewWillLayoutSubviews() {
        super.viewWillLayoutSubviews()
        print("MainViewController bounds = \(self.view.bounds)")
    }

这给出了一个有趣的打印（在iPhone 13 Mini上运行此码）模拟器）：

MainViewController bounds = (0.0, 0.0, 375.0, 812.0) //iPhone 13 mini screen is 375 x 812
ChildViewControllerA bounds = (0.0, 0.0, 375.0,738.0). // 812 - 50 safety margin - 24 titlebar = 738.

现在，在单击按钮并添加了ChildViewControllerb之后发生的开关发生：

ChildViewControllerB bounds = (0.0, 0.0, 375.0, 812.0)

似乎ChildViewControllerb假设全屏幕大小并忽略其父级视图控制器的边界（containerServiewController）。因此，ImageView的Hightanchor基于全屏高度，导致其出现在中间。

因此，我将图像视图上的约束更改为：

NSLayoutConstraint.activate([
        imageView.centerYAnchor.constraint(equalTo: super.view.centerYAnchor),
        imageView.centerXAnchor.constraint(equalTo: super.view.centerXAnchor),
        imageView.heightAnchor.constraint(equalTo: super.view.heightAnchor, multiplier: 0.6),
    ])

接下来，我尝试通过添加任何这些行在上面的showextviewcontroller（）函数上以上：

container.children.first?.view.layoutSubviews()

//and

container.children.first?.view.setNeedsLayout()

它们都没有使用后，尝试强制布局更新。

如何获得ChildViewControllerb来尊重ContainerServiewController的界限？

如果有帮助，则图像视图最初只需要位于中心。它最终会附着一个锅，捏和旋转的手势，因此用户可以将其移动到任何地方。

编辑01：

这是我要添加和删除子查看控制器的方式：

extension UIViewController {
    func addViewController(_ child: UIViewController) {
        addChild(child)
        view.addSubview(child.view)
        child.didMove(toParent: self)
    }
    
    func remove() {
        guard parent != nil else { return }
        willMove(toParent: nil)
        view.removeFromSuperview()
        removeFromParent()
    }
}

编辑02：

在一些评论员的推荐下，我更新了AddViewController（）函数

func addViewController(_ child: UIViewController) {
        
        addChild(child)
        view.addSubview(child.view)
        
        child.view.translatesAutoresizingMaskIntoConstraints = false
        
        NSLayoutConstraint.activate([
            child.view.topAnchor.constraint(equalTo: self.view.topAnchor),
            child.view.leadingAnchor.constraint(equalTo: self.view.leadingAnchor),
            child.view.trailingAnchor.constraint(equalTo: self.view.trailingAnchor),
            child.view.bottomAnchor.constraint(equalTo: self.view.bottomAnchor),
        ])
        
        
        child.didMove(toParent: self)
        
    }

：似乎没有用，我遇到了错误，说“无法同时满足约束”。不幸的是，我对如何破译错误消息的知识很少...

编辑03：简化项目：

这是一个简化的项目。有四个文件加上AppDelegate（我不使用故事板）：

• MainViewController
• ViewControllera
• ViewControllerb
• 实用程序
• AppDelegate

MainViewController：

import UIKit

class MainViewController: UIViewController {
    
    let titleBarView = UIView(frame: .zero)
    let container = UIViewController()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        setup()
        layout()
    }
    
    func setup() {
        
        titleBarView.backgroundColor = .gray
        view.addSubview(titleBarView)
        
        addViewController(container)
        showViewControllerA()
    }
    
    func layout() {
        titleBarView.translatesAutoresizingMaskIntoConstraints = false
        container.view.translatesAutoresizingMaskIntoConstraints = false
        
        NSLayoutConstraint.activate([
            titleBarView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor),
            titleBarView.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            titleBarView.trailingAnchor.constraint(equalTo: view.trailingAnchor),
            titleBarView.heightAnchor.constraint(equalToConstant: 24),

            container.view.topAnchor.constraint(equalTo: titleBarView.bottomAnchor, constant: 0),
            container.view.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            container.view.trailingAnchor.constraint(equalTo: view.trailingAnchor),
            container.view.bottomAnchor.constraint(equalTo: view.bottomAnchor),
        ])
    }
    
    func showViewControllerA() {
        let viewControllerA = ViewControllerA()
        viewControllerA.delegate = self
        
        container.children.first?.remove()
        container.addViewController(viewControllerA)
    }
    
    func showViewControllerB() {
        let viewControllerB = ViewControllerB()
        
        container.children.first?.remove()
        container.addViewController(viewControllerB)
    }
}

extension MainViewController: ViewControllerADelegate {
    func nextViewController() {
        showViewControllerB()
    }
}

ViewController A：ViewController a：

protocol ViewControllerADelegate: AnyObject {
    func nextViewController()
}

class ViewControllerA: UIViewController {
    
    let nextButton = UIButton()
    
    weak var delegate: ViewControllerADelegate?
    
    override func viewDidLoad() {
        super.viewDidLoad()
        setup()
        layout()
        view.backgroundColor = .gray
    }
    
    func setup() {
        nextButton.setTitle("next", for: .normal)
        nextButton.addTarget(self, action: #selector(nextButtonPressed), for: .primaryActionTriggered)
        view.addSubview(nextButton)
    }
    
    func layout() {
        nextButton.translatesAutoresizingMaskIntoConstraints = false
        
        NSLayoutConstraint.activate([
            nextButton.centerXAnchor.constraint(equalTo: view.centerXAnchor),
            nextButton.centerYAnchor.constraint(equalTo: view.centerYAnchor)
        ])
    }
    
    @objc func nextButtonPressed() {
        delegate?.nextViewController()
    }  
}

viewController b：

import import uikit uikit

class ViewControllerB: UIViewController {
    
    let imageView = UIImageView()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        setup()
        layout()
    }
    
    func setup() {
        view.addSubview(imageView)
        blankImage()
    }
    
    func layout() {
        imageView.translatesAutoresizingMaskIntoConstraints = false
        imageView.contentMode = .scaleAspectFill
        imageView.layer.magnificationFilter = CALayerContentsFilter.nearest;
       

        NSLayoutConstraint.activate([
            imageView.centerYAnchor.constraint(equalTo: super.view.centerYAnchor),
            imageView.centerXAnchor.constraint(equalTo: super.view.centerXAnchor),
            imageView.heightAnchor.constraint(equalTo: super.view.heightAnchor, multiplier: 0.6),
        ])
        
        view.layoutSubviews()

    }
    
    func blankImage() {
        let ciImage = CIImage(cgImage: createBlankCGImage(width: 32, height: 64)!)
        imageView.image = cIImageToUIImage(ciimage: ciImage, context: CIContext())
    }
}

Utilities

import Foundation
import UIKit

func createBlankCGImage(width: Int, height: Int) -> CGImage? {
    
    let bounds = CGRect(x: 0, y:0, width: width, height: height)
    let intWidth = Int(ceil(bounds.width))
    let intHeight = Int(ceil(bounds.height))
    let bitmapContext = CGContext(data: nil,
                                  width: intWidth, height: intHeight,
                                  bitsPerComponent: 8,
                                  bytesPerRow: 0,
                                  space: CGColorSpace(name: CGColorSpace.sRGB)!,
                                  bitmapInfo: CGImageAlphaInfo.premultipliedLast.rawValue)

    if let cgContext = bitmapContext {
        cgContext.saveGState()
        let r = CGFloat.random(in: 0...1)
        let g = CGFloat.random(in: 0...1)
        let b = CGFloat.random(in: 0...1)
        
        cgContext.setFillColor(red: r, green: g, blue: b, alpha: 1)
        cgContext.fill(bounds)
        cgContext.restoreGState()
        
        return cgContext.makeImage()
    }
    
    return nil
}

func cIImageToUIImage(ciimage: CIImage, context: CIContext) -> UIImage? {
    if let cgimg = context.createCGImage(ciimage, from: ciimage.extent) {
        return UIImage(cgImage: cgimg)
    }
    return nil
}


extension UIViewController {
    
    func addViewController(_ child: UIViewController) {
        addChild(child)
        view.addSubview(child.view)
        child.didMove(toParent: self)
    }
    
    func remove() {
        guard parent != nil else { return }
        willMove(toParent: nil)
        view.removeFromSuperview()
        removeFromParent()
    }
}

：appdelegate：appdelegate：appdelegate：appdelegate：appdelegate ：：

import UIKit

@main
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?
    
    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        window = UIWindow(frame: UIScreen.main.bounds)
        window?.backgroundColor = .white
        window?.makeKeyAndVisible()
        
        window?.rootViewController = MainViewController()
        
        return true
    }
}

Answer 1

小行星在正确的轨道上，但是其他问题……

您没有给子控制器的视图任何约束，因此它们以“本地”大小加载。

建议，更改addViewController（...） func求解a和b缺少约束，但是...

如小行星 您的容器 Controller 和 在layout（）中添加约束，因此您最终会添加约束矛盾的约束。

一种解决方案是将您的addViewController func更改为：

func addViewController(_ child: UIViewController, constrainToSuperview: Bool = true) {
    addChild(child)
    view.addSubview(child.view)
    
    if constrainToSuperview {
        child.view.translatesAutoresizingMaskIntoConstraints = false
        NSLayoutConstraint.activate([
            child.view.topAnchor.constraint(equalTo: view.topAnchor),
            child.view.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            child.view.trailingAnchor.constraint(equalTo: view.trailingAnchor),
            child.view.bottomAnchor.constraint(equalTo: view.bottomAnchor),
        ])
    }
    
    child.didMove(toParent: self)
}

然后在setup（）中：

func setup() {
    
    titleBarView.backgroundColor = .red
    view.addSubview(titleBarView)

    // change this
    //addViewController(container)
    
    // to this
    addViewController(container, constrainToSuperview: false)

    showViewControllerA()
}

在留下其他“添加视图控制器”呼叫时

container.addViewController(viewControllerA)
container.addViewController(viewControllerB)

：将您丢掉的是图像查看约束中的无关 super。：

    NSLayoutConstraint.activate([
        // change this
        //imageView.centerYAnchor.constraint(equalTo: super.view.centerYAnchor),
        //imageView.centerXAnchor.constraint(equalTo: super.view.centerXAnchor),
        //imageView.heightAnchor.constraint(equalTo: super.view.heightAnchor, multiplier: 0.6),

        // to this
        imageView.centerYAnchor.constraint(equalTo: view.centerYAnchor),
        imageView.centerXAnchor.constraint(equalTo: view.centerXAnchor),
        imageView.heightAnchor.constraint(equalTo: view.heightAnchor, multiplier: 0.6),
    ])
    

Answer 2

如下：

func addViewController(_ child: UIViewController) {
    addChild(child)
    view.addSubview(child.view)
    child.didMove(toParent: self)
        
    child.view.translatesAutoresizingMaskIntoConstraints = false

    NSLayoutConstraint.activate([
        child.view.leadingAnchor.constraint(equalTo: view.leadingAnchor),
        child.view.trailingAnchor.constraint(equalTo: view.trailingAnchor),
        child.view.topAnchor.constraint(equalTo: view.topAnchor),
        child.view.bottomAnchor.constraint(equalTo: view.bottomAnchor)])
}
    

在 mainviewViewController中

func layout() {
    titleBarView.translatesAutoresizingMaskIntoConstraints = false
    container.view.translatesAutoresizingMaskIntoConstraints = false
        
    NSLayoutConstraint.activate([
        titleBarView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor),
        titleBarView.leadingAnchor.constraint(equalTo: view.leadingAnchor),
        titleBarView.trailingAnchor.constraint(equalTo: view.trailingAnchor),
        titleBarView.heightAnchor.constraint(equalToConstant: 24),

        //container.view.topAnchor.constraint(equalTo: titleBarView.bottomAnchor, constant: 0),
        //container.view.leadingAnchor.constraint(equalTo: view.leadingAnchor),
        //container.view.trailingAnchor.constraint(equalTo: view.trailingAnchor),
        //container.view.bottomAnchor.constraint(equalTo: view.bottomAnchor),
    ])
        
}