SwiftUI 中的可选 @ObservableObject [英] Optional @ObservableObject in SwiftUI

问题描述

我想在 SwiftUI 中有一个可选的 @ObservedObject，但我一直收到编译时错误.

I want to have an optional @ObservedObject in SwiftUI but I keep getting a compile time error of.

Property type 'AModel?' does not match that of the 'wrappedValue' property of its wrapper type 'ObservedObject'

这是一些最低限度的可重现代码.

Here is some minimum reproducible code.

import SwiftUI

public struct AView: View {
    
    //MARK: View Model
    //Error thrown here.
    @ObservedObject var model: AModel?
    
    //MARK: Body
    public var body: some View {
        Text("\(model?.value ?? 0)")
    }
    
    //MARK: Init
    public init() {
        
    }
    
}

class AModel: ObservableObject {
    let value: Int = 0
}

推荐答案

技术原因是 Optional 不是一个类，所以不能符合 ObservableObject.

The technical reason is that Optional is not a class, so it cannot be conformed to ObservableObject.

但是如果你想避免重构对象本身——例如，如果它不在你的控制范围内——你可以这样做:

But if you want to avoid refactoring the object itself - for example, if it's not in your control - you could do something like this:

struct AView: View {

    private struct Content: View {
       @ObservedObject var model: AModel
       var body: some View {
          Text("\(model.value)")
       }
    }

    var model: AModel?
    
    var body: some View {
       if let model = model {
          Content(model: model)
       } else {
          Text("0")
       }
    }    
}

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