ios - 如何在 SwiftUI 中实现自定义委托(delegate)

Question

例如，我有一个 SwitUI ContentView。当您第一次制作项目时出现的那个。

import SwiftUI

struct ContentView: View {
   var manager = TestManager()
   var body: some View {
    ZStack{
        Color(.green)
            .edgesIgnoringSafeArea(.all)
        VStack {
            Text("Test Text")

            Button(action:{}) {
                Text("Get number 2")
                    .font(.title)
                    .foregroundColor(.white)
                .padding()
                .overlay(RoundedRectangle(cornerRadius: 30)
                .stroke(Color.white, lineWidth: 5))
                }
           }
       }
   }
}

我有一个将处理 Api 调用的 TestManager。我为具有两个功能的类做了一个委托(delegate)。

protocol TestManagerDelegate {
    func didCorrectlyComplete(_ testName: TestManager, model: TestModel)
    func didFailWithError(_ error: Error)
}

struct TestManager {

    var delegate: TestManagerDelegate?
    let urlString = "http://numbersapi.com/2/trivia?json"

    func Get(){
        if let url = URL(string: urlString){

            let session = URLSession(configuration: .default)

            let task = session.dataTask(with: url) { (data, response, error) in
                if error != nil{
                    self.delegate?.didFailWithError(error!)
                    return
                }

                if let safeData = data{
                    if let parsedData = self.parseJson(safeData){
                        self.delegate?.didCorrectlyComplete(self, model: parsedData)
                    }
                }
            }
            task.resume()
        }
    }

   func parseJson(_ jsonData: Data) -> TestModel?{
       let decoder = JSONDecoder()
       do {
           let decodedData = try decoder.decode(TestModel.self,  from: jsonData)
           let mes = decodedData.message
           let model = TestModel(message: mes)
           return model

       } catch {
           delegate?.didFailWithError(error)
           return nil
       }
     }

  }

这是 testModel 数据类。只抓取返回的 Json 文本。

struct TestModel :Decodable{
    let text: String
}

如何将 TestManager 连接到 View 并让 View 处理委托(delegate)，就像我们在 Storyboard 中所做的那样？

Answer 1

关于TestModel

Decodable协议(protocol)(在您的上下文中)假设您使用通过 JSON 获得的所有属性创建模型结构。当请求 http://numbersapi.com/2/trivia?json你会得到类似的东西:

{
 "text": "2 is the number of stars in a binary star system (a stellar system consisting of two stars orbiting around their center of mass).",
 "number": 2,
 "found": true,
 "type": "trivia"
}

这意味着，您的模型应如下所示:

struct TestModel: Decodable {
    let text: String
    let number: Int
    let found: Bool
    let type: String
}

关于委托(delegate)

在 SwiftUI 中，这种方法是无法实现的。相反，开发人员需要调整 Combine 框架的特性:属性包装器 @ObservedObject , @Published , 和 ObservableObject协议(protocol)。
您想将逻辑放入某个结构中。坏消息，(目前) ObservableObject是 AnyObject协议(protocol)(即 Class-Only Protocol )。你需要重写你的 TestManager作为类:

class TestManager: ObservableObject {
   // ...
}

只有这样你才能在你的 CurrentView 中使用它。使用 @ObservedObject属性包装器:

struct ContentView: View {
    @ObservedObject var manager = TestManager()
    // ...
}

关于TestManager

您的逻辑现在排除了 delegate因此，您需要使用您的 TestModel将数据传递给您的 CustomView .您可以修改 TestManager通过使用 @Published 添加新属性属性包装器:

class TestManager: ObservableObject {
    let urlString = "http://numbersapi.com/2/trivia?json"
    // 1
    @Published var model: TestModel?

    func get(){
        if let url = URL(string: urlString){
            let session = URLSession(configuration: .default)
            let task = session.dataTask(with: url) { [weak self] (data, response, error) in
                // 2
                DispatchQueue.main.async { 
                    if let safeData = data {
                        if let parsedData = self?.parseJson(safeData) {
                            // 3
                            self?.model = parsedData
                        }
                    }
                }
            }
            task.resume()
        }
    }

    private func parseJson(_ jsonData: Data) -> TestModel? {
        let decoder = JSONDecoder()
        do {
            let decodedData = try decoder.decode(TestModel.self, from: jsonData)
            return decodedData
        } catch {
            return nil
        }
    }
}

为了能够“从外部”访问您的模型，在您的情况下为 ContentView .

使用DispatchQueue.main.async{ }对于异步任务，因为 Publishing changes from background threads is not allowed; make sure to publish values from the main thread (via operators like receive(on:)) on model updates.

只需使用您解析的模型。

然后在 ContentView使用您的 TestManager像这样:

struct ContentView: View {
    @ObservedObject var manager = TestManager()
    var body: some View {
        ZStack{
            Color(.green)
                .edgesIgnoringSafeArea(.all)
            VStack {
                Text("Trivia is: \(self.manager.model?.text ?? "Unknown")")
                Button(action:{ self.manager.get() }) {
                    Text("Get number 2")
                        .font(.title)
                        .foregroundColor(.white)
                        .padding()
                        .overlay(RoundedRectangle(cornerRadius: 30)
                            .stroke(Color.white, lineWidth: 5))
                }
            }
        }
    }
}

关于 HTTP

您使用链接 http://numbersapi.com/2/trivia?json这是 not allowed by Apple ，请使用 https相反，或添加 App Transport Security Settings带有 Allow Arbitrary Loads 的键参数设置为 YES into your Info.Plist .但是这样做 very carefully因为http链接根本不起作用。

进一步的步骤

您可以根据上面的描述自行实现错误处理。

完整代码(复制粘贴):

import SwiftUI

struct ContentView: View {
    @ObservedObject var manager = TestManager()
    var body: some View {
        ZStack{
            Color(.green)
                .edgesIgnoringSafeArea(.all)
            VStack {
                Text("Trivia is: \(self.manager.model?.text ?? "Unknown")")
                Button(action:{ self.manager.get() }) {
                    Text("Get number 2")
                        .font(.title)
                        .foregroundColor(.white)
                        .padding()
                        .overlay(RoundedRectangle(cornerRadius: 30)
                            .stroke(Color.white, lineWidth: 5))
                }
            }
        }
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}

class TestManager: ObservableObject {
    let urlString = "http://numbersapi.com/2/trivia?json"
    @Published var model: TestModel?

    func get(){
        if let url = URL(string: urlString){
            let session = URLSession(configuration: .default)
            let task = session.dataTask(with: url) { [weak self] (data, response, error) in
                DispatchQueue.main.async {
                    if let safeData = data {
                        if let parsedData = self?.parseJson(safeData) {
                            self?.model = parsedData
                        }
                    }
                }
            }
            task.resume()
        }
    }

    private func parseJson(_ jsonData: Data) -> TestModel? {
        let decoder = JSONDecoder()
        do {
            let decodedData = try decoder.decode(TestModel.self, from: jsonData)
            return decodedData
        } catch {
            return nil
        }
    }
}

struct TestModel: Decodable {
    let text: String
    let number: Int
    let found: Bool
    let type: String
}