值更改时如何在 UIKit 中更新 SwiftUI 视图？

Posted 2023-02-24

【中文标题】值更改时如何在 UIKit 中更新 SwiftUI 视图？

【英文标题】：How do I update a SwiftUI View in UIKit when value changes?

【发布时间】：2020-02-06 00:19:30

【问题描述】：

我正在尝试将一个 SwiftUI 视图集成到一个现有的 UIKit 应用程序中，该视图在更改 @State 变量时进行动画处理（最初的进度是 @State 私有进度：SwiftUI 视图中的 CGFloat = 0.5） .我已经阅读了大量关于将 SwiftUI 集成到 UIKit（@State、@Binding、@Environment 等）的搜索结果，但似乎无法弄清楚这一点。

我创建了一个非常简单的示例来说明我正在尝试做的事情，因为我相信一旦我看到这个答案，我就可以将它应用到我现有的应用程序中。

Storyboard 只是带有 UISlider 的视图控制器。下面的代码显示了 SwiftUI 视图，但我希望它在我移动 UISlider 时更新。

import SwiftUI

class ViewController: UIViewController 

    var progress: CGFloat = 0.5

    override func viewDidLoad() 
        super.viewDidLoad()
        // Do any additional setup after loading the view.

        let frame = CGRect(x: 20, y: 200, width: 400, height: 400)

        let childView = UIHostingController(rootView: Animate_Trim(progress: progress))
        addChild(childView)
        childView.view.frame = frame
        view.addSubview(childView.view)
        childView.didMove(toParent: self)
    

    @IBAction func sliderAction(_ sender: UISlider) 
        progress = CGFloat(sender.value)
        print("Progress: \(progress)")
    



struct Animate_Trim: View 
    var progress: CGFloat

    var body: some View 
        VStack(spacing: 20) 

            Circle()
                .trim(from: 0, to: progress) // Animate trim
                .stroke(Color.blue,
                        style: StrokeStyle(lineWidth: 40,
                                           lineCap: CGLineCap.round))
                .frame(height: 300)
                .rotationEffect(.degrees(-90)) // Start from top
                .padding(40)
                .animation(.default)

            Spacer()

        .font(.title)
    
```

【参考方案1】：

接受的答案实际上并没有回答原始问题“在 UIKit 中更新 SwiftUI 视图...”？

恕我直言，当您想与 UIKit 交互时，您可以使用通知来更新进度视图：

extension Notification.Name 
  static var progress: Notification.Name  return .init("progress") 

class ViewController: UIViewController 
  var progress: CGFloat = 0.5 
    didSet 
      let userinfo: [String: CGFloat] = ["progress": self.progress]
      NotificationCenter.default.post(Notification(name: .progress,
                                                   object: nil,
                                                   userInfo: userinfo))
    
  
  var slider: UISlider = UISlider()
  override func viewDidLoad() 
    super.viewDidLoad()
    slider.addTarget(self, action: #selector(sliderAction(_:)), for: .valueChanged)
    slider.frame = CGRect(x: 0, y: 500, width: 200, height: 50)
    // Do any additional setup after loading the view.

    let frame = CGRect(x: 20, y: 200, width: 400, height: 400)

    let childView = UIHostingController(rootView: Animate_Trim())
    addChild(childView)
    childView.view.frame = frame
    view.addSubview(childView.view)
    view.addSubview(slider)
    childView.didMove(toParent: self)
  

  @IBAction func sliderAction(_ sender: UISlider) 
    progress = CGFloat(sender.value)
    print("Progress: \(progress)")
  


struct Animate_Trim: View 
  @State var progress: CGFloat = 0
  var notificationChanged = NotificationCenter.default.publisher(for: .progress)
  var body: some View 
    VStack(spacing: 20) 
      Circle()
        .trim(from: 0, to: progress) // Animate trim
        .stroke(Color.blue,
                style: StrokeStyle(lineWidth: 40,
                                   lineCap: CGLineCap.round))
        .frame(height: 300)
        .rotationEffect(.degrees(-90)) // Start from top
        .padding(40)
        .animation(.default)
        .onReceive(notificationChanged)  note in
          self.progress = note.userInfo!["progress"]! as! CGFloat
      
      Spacer()
    .font(.title)
  

【讨论】：

这看起来有点矫枉过正，没有更简单的方法可以从 UIKit 更新 SwiftUI 中的 @Binding 变量吗？

【参考方案2】：

如果您不想使用通知中心。您可以只使用 @Published 并分配或接收。

我在 Playground 中编写了一个工作示例来展示这个概念：

//This code runs on Xcode playground
import Combine
import SwiftUI

class ObservableSlider: ObservableObject 
    @Published public var value: Double = 0.0


class YourViewController 
    var observableSlider:ObservableSlider = ObservableSlider()
    private var cancellables: Set<AnyCancellable> = []
    let hostController = YourHostingController() // I put it here for the sake of the example, but you do need a reference to the Hosting Controller.

    init() // In a real VC this code would probably be on viewDidLoad

        let swiftUIView = hostController.rootView

        //This is where values of SwiftUI view and UIKit get glued together
        self.observableSlider.$value.assign(to: \.observableSlider.value, on: swiftUIView).store(in:&self.cancellables)
    
    func updateSlider() 
        observableSlider.value = 8.5
    


// In real app it would be something like:
//class YourHostingController<YourSwiftUIView> UIHostingController
class YourHostingController 
    var rootView = YourSwiftUIView()

//In a real Hosting controller you would do something like:
//    required init?(coder aDecoder: NSCoder)
//         super.init(coder: aDecoder, rootView: YourSwiftUIView())
//     


struct YourSwiftUIView: View
    var body: some View 
        EmptyView() // Your real SwiftUI body...
    
    @ObservedObject var observableSlider: ObservableSlider = ObservableSlider()
    func showValue()
        print(observableSlider.value)
    
    init()
        print(observableSlider.value)
    


let yourVC = YourViewController() // Inits view and prints 0.0
yourVC.updateSlider() // Updates from UIKit to 8.5
yourVC.hostController.rootView.showValue() // Value in SwiftUI View is updated (prints 8.5)

【参考方案3】：

Combine 是你的朋友......

创建模型 从 UISlider 或应用程序的任何其他部分更新模型 使用模型更新您的 SwiftUI.View

我做了简单的例子，只使用 SwiftUI，但使用相同的场景

import SwiftUI

class Model: ObservableObject 
    @Published var progress: Double = 0.2



struct SliderView: View 
    @EnvironmentObject var slidermodel: Model
    var body: some View 

        // this is not part of state of the View !!!
        // the bindig is created directly to your global EnnvironmentObject

        // be sure that it is available by
        // creating the SwiftUI view that provides the window contents
        // in your SceneDelegate.scene(....)
        // let model = Model()
        // let contentView = ContentView().environmentObject(model)

        let binding = Binding<Double>(get:  () -> Double in
            self.slidermodel.progress
        )  (value) in
            self.slidermodel.progress = value
        

        return Slider(value: binding, in: 0.0 ... 1.0)
    



struct ContentView: View 
    @EnvironmentObject var model: Model
    var body: some View 
        VStack 

            Circle()
                .trim(from: 0, to: CGFloat(model.progress)) // Animate trim
                .stroke(Color.blue,
                        style: StrokeStyle(lineWidth: 40,
                                           lineCap: CGLineCap.round))
                .frame(height: 300)
                .rotationEffect(.degrees(-90)) // Start from top
                .padding(40)
                .animation(.default)

            SliderView()
        
    


struct ContentView_Previews: PreviewProvider 
    static var previews: some View 
        ContentView().environmentObject(Model())
    

一切都很好地协同工作

【讨论】：

这很酷，但没有直接回答关于从 UIKit 更新 SwiftUI 的 OP

如前所述，这根本不使用 UIKit。