为什么 SwiftUI UIHostingController 有额外的间距？

Question

我正在尝试使用 UIHostingController 将 SwiftUI 视图添加到 UIKit 视图，它显示了额外的间距（此示例用于模拟生产应用程序上的问题）。这是屏幕截图。

布局概览：

View
  UIStackView
    UIImageView
    UIView(red)
    UIHostingController
    UIView(blue)

问题： swift UI 视图 (UIHostingController) 显示在红色和蓝色视图之间，它在分隔线后显示额外的间距。间距根据 SwiftUI 视图的大小而变化。

如果我减少行数（Hello World 文本）或减少间距，它似乎工作正常。

这里是完整的源代码(https://www.sendspace.com/file/ux0xt7)：

ViewController.swift（主视图）

import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var mainStackView: UIStackView!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
        
        addView()
    }


    private func addView() {
        mainStackView.spacing = 0
        mainStackView.alignment = .fill
        
        let imageView = UIImageView()
        imageView.image = UIImage(named: "mountain")
        imageView.contentMode = .scaleAspectFill
        imageView.clipsToBounds = true
        imageView.heightAnchor.constraint(equalToConstant: 260).isActive = true
        mainStackView.addArrangedSubview(imageView)
        
        let redView = UIView()
        redView.backgroundColor = .red
        redView.heightAnchor.constraint(equalToConstant: 100).isActive = true
        mainStackView.addArrangedSubview(redView)
        
        
        
        let sampleVC = SampleViewController()
        //let size = sampleVC.view.systemLayoutSizeFitting(UIView.layoutFittingCompressedSize)
        //sampleVC.view.heightAnchor.constraint(equalToConstant: size.height).isActive = true
        mainStackView.addArrangedSubview(sampleVC.view)
        
        
        let blueView = UIView()
        blueView.backgroundColor = .blue
        blueView.heightAnchor.constraint(equalToConstant: 100).isActive = true
        mainStackView.addArrangedSubview(blueView)
    }
}

SampleView.swift

import SwiftUI

struct SampleView: View {
    var body: some View {
        VStack(spacing: 0) {
            Text("Title")

            VStack (alignment: .leading, spacing: 30) {
                Text("Hello World1")
                Text("Hello World2")
                Text("Hello World3")
                Text("Hello World4")
                Text("Hello World5")
                Text("Hello World6")
                Text("Hello World7")
                Text("Hello World8")
                Text("Hello World9")
                Text("Hello World10")
            }
            Divider()
        }
        
    }
}



struct SampleView_Previews: PreviewProvider {

    
    static var previews: some View {
        Group {
            SampleView()
        }
    }
}

SampleViewController.swift

import UIKit
import SwiftUI

class SampleViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        
        addView()
    }
    
    private func addView() {
        let hostingController = UIHostingController(rootView: SampleView())
        
        hostingController.view.backgroundColor = .clear
        hostingController.view.translatesAutoresizingMaskIntoConstraints = false
        addChild(hostingController)
        view.addSubview(hostingController.view)
        hostingController.didMove(toParent: self)
        
        NSLayoutConstraint.activate([
            hostingController.view.leadingAnchor.constraint(equalTo: self.view.leadingAnchor),
            hostingController.view.trailingAnchor.constraint(equalTo: self.view.trailingAnchor),
            hostingController.view.topAnchor.constraint(equalTo: self.view.topAnchor, constant: 0),
            hostingController.view.bottomAnchor.constraint(equalTo: self.view.bottomAnchor)
        ])
    }
}

提前致谢！

Answer 1

除了UIView(red)，您可以简单地使用Color.red 与UIView(blue) 相同：

struct SampleView: View {
    var body: some View {
        
        VStack(spacing: .zero) {
            
            Color.red
            
            Text("Title")

            VStack (alignment: .leading, spacing: 30) {
                Text("Hello World1")
                Text("Hello World2")
                Text("Hello World3")
                Text("Hello World4")
                Text("Hello World5")
                Text("Hello World6")
                Text("Hello World7")
                Text("Hello World8")
                Text("Hello World9")
                Text("Hello World10")
            }
            
            Divider()
            
            Color.blue.opacity(0.1)
        }
 
    }
}

---

结果：

Answer 2

让宿主控制器的视图再次更新其布局：

class SampleViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        
        addView()
    }
    
    private func addView() {
        let hostingController = UIHostingController(rootView: SampleView())
        
        hostingController.view.backgroundColor = .clear
        hostingController.view.translatesAutoresizingMaskIntoConstraints = false
        addChild(hostingController)
        view.addSubview(hostingController.view)
        hostingController.didMove(toParent: self)
        
        NSLayoutConstraint.activate([
            hostingController.view.leadingAnchor.constraint(equalTo: self.view.leadingAnchor),
            hostingController.view.trailingAnchor.constraint(equalTo: self.view.trailingAnchor),
            hostingController.view.topAnchor.constraint(equalTo: self.view.topAnchor, constant: 0),
            hostingController.view.bottomAnchor.constraint(equalTo: self.view.bottomAnchor)
        ])
        
        hostingController.view.layoutIfNeeded()
    }

}

Answer 3

我遇到了类似的问题，就像 @Asperi mentions，由于 SwiftUI 视图应用了额外的安全区域插图。

很遗憾，简单地将edgesIgnoringSafeArea() 添加到 SwiftUI 视图中是行不通的。

相反，您可以使用以下 UIHostingController 扩展来解决此问题：

extension UIHostingController {
    convenience public init(rootView: Content, ignoreSafeArea: Bool) {
        self.init(rootView: rootView)
        
        if ignoreSafeArea {
            disableSafeArea()
        }
    }
    
    func disableSafeArea() {
        guard let viewClass = object_getClass(view) else { return }
        
        let viewSubclassName = String(cString: class_getName(viewClass)).appending("_IgnoreSafeArea")
        if let viewSubclass = NSClassFromString(viewSubclassName) {
            object_setClass(view, viewSubclass)
        }
        else {
            guard let viewClassNameUtf8 = (viewSubclassName as NSString).utf8String else { return }
            guard let viewSubclass = objc_allocateClassPair(viewClass, viewClassNameUtf8, 0) else { return }
            
            if let method = class_getInstanceMethod(UIView.self, #selector(getter: UIView.safeAreaInsets)) {
                let safeAreaInsets: @convention(block) (AnyObject) -> UIEdgeInsets = { _ in
                    return .zero
                }
                class_addMethod(viewSubclass, #selector(getter: UIView.safeAreaInsets), imp_implementationWithBlock(safeAreaInsets), method_getTypeEncoding(method))
            }
            
            objc_registerClassPair(viewSubclass)
            object_setClass(view, viewSubclass)
        }
    }
}

并像这样使用它：

let hostingController = UIHostingController(rootView: SampleView(), ignoreSafeArea: true)

解决方案出处：https://defagos.github.io/swiftui_collection_part3/#fixing-cell-frames