-1

ObservableObject 类是从 ContentView() 和另一个 Swift 类中实例化的。当 Swift 类运行 ObservableObject 类的函数时，它不会更新 ContentView() 的 @ObservedObject。

我知道这是因为我两次实例化 ObservableObject 类。当 ContentView() 不能/不能实例化 Observable 类时，使用 @ObservedObject 的最佳做法是什么？

我还没有找到让 @EnvironmentObject 与 Swift 类一起工作的方法。
我可以使用全局变量并运行 Timer() 来检查对它的更改。但是，这感觉像是一种丑陋的做法？！？

请参阅下面的示例代码。请在设备上运行，以查看打印语句。


import SwiftUI

struct ContentView: View {
    
    @ObservedObject var observedClass: ObservedClass = ObservedClass()
    
    // The callingObservedClass does not exist on the ContentView, but is called
    // somewhere in the app with no reference to the ContentView.
    // It is included here to better showcase the issue.
   
    let callingObservedClass: CallingObservedClass = CallingObservedClass()
    
    var body: some View {
        
        VStack {
   
            // This Text shall be updated, when
            // self.callingObservedClass.increaseObservedClassCount() has been executed.
   
            Text(String(observedClass.count))
            
            Button(action: {
    
                // This updates the count-variable, but as callingObservedClass creates
                // a new instance of ObservedClass, the Text(observedClass.count) is not updated.
   
                self.callingObservedClass.increaseObservedClassCount()
            }, label: {
                Text("Increase")
            })
        }
    }
}


class CallingObservedClass {
    
    let observedClass = ObservedClass()
    
    func increaseObservedClassCount() {
   
        // Returning an Int here to better showcase that count is increased.
        // But not in the ObservedClass instance of the ContentView, as the
        // Text(observedClass.count) remains at 0.
    
        let printCount = observedClass.increaseCount()
        print(printCount)
    }
}


class ObservedClass: ObservableObject {
    @Published var count: Int = 0
    
    func increaseCount() -> Int {
        count = count + 1
        return count
    }
}


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

编辑：我想我的问题是当我无法从 SwiftUI 视图实例化 Swift 类时，如何从 Swift 类获取数据并更新 SwiftUI 视图。

4

1 回答 1

0

一个可能的解决方案是链接 ObservableObject 类。不幸的是，从 iOS 13.6 开始，这并不是开箱即用的。

我通过以下方式找到了答案： 如何告诉 SwiftUI 视图绑定到嵌套的 ObservableObjects

调整和运行示例：

// Add Combine

import Combine
import SwiftUI

struct ContentView: View {

    @ObservedObject var callingObservedClass: CallingObservedClass = CallingObservedClass()
    
    var body: some View {
        
        VStack {

            // Calling the chained ObservableObject
            
            Text(String(callingObservedClass.observedClass.count))
            
            Button(action: {

                self.callingObservedClass.increaseObservedClassCount()
            }, label: {
                Text("Increase")
            })
        }
    }
}

class CallingObservedClass: ObservableObject {
    
    // Chaining Observable Objects
    
    @Published var observedClass = ObservedClass()
    
    // ObservableObject-chaining does not work out of the box.
    // The anyCancellable variable with the below init() will do the trick.
    // Thanks to https://stackoverflow.com/questions/58406287/how-to-tell-swiftui-views-to-bind-to-nested-observableobjects
    
    var anyCancellable: AnyCancellable? = nil
    
    init() {
        anyCancellable = observedClass.objectWillChange.sink { (_) in
            self.objectWillChange.send()
        }
    }
    
    func increaseObservedClassCount() {
        let printCount = observedClass.increaseCount()
        print(printCount)
    }
}

class ObservedClass: ObservableObject {
    @Published var count: Int = 0
    
    func increaseCount() -> Int {
        count = count + 1
        return count
    }
}


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

如果 ObservableObject-Chaining 不是一个选项，我对如何访问 Swift 类数据和更新 SwiftUI 视图很感兴趣。

如果您对此有解决方案，请在下面回答。

于 2020-07-29T14:35:44.070 回答