SwiftUI - 从 Swift 类启动的可观察对象不会更新 ContentView() 上的 @ObservedObject

Posted 2023-02-24

【中文标题】SwiftUI - 从 Swift 类启动的可观察对象不会更新 ContentView() 上的 @ObservedObject

【英文标题】：SwiftUI - Observable Object initiated from Swift class does not update @ObservedObject on ContentView()

【发布时间】：2020-07-29 11:53:01

【问题描述】：

ObservableObject 类是从 ContentView() 和另一个 Swift 类实例化的。 ObservableObject类的函数在Swift类运行时，不会更新ContentView()的@ObservedObject。

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

我还没有找到让@EnvironmentObject 与 Swift 类一起使用的方法。 我可以使用全局变量并运行 Timer() 来检查对它的更改。然而，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，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。

【参考方案1】：

一个可能的解决方案是链接 ObservableObject 类。不幸的是，从 ios 13.6 开始，这不能开箱即用。

我通过以下方式找到了答案： How to tell SwiftUI views to bind to nested 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://***.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。