面對 State 的一些奇怪行為或 SwiftUI 中的 didSet 情況下的綁定

Question

I am updating my State variable with a Binding from another View, I have some code in didSet of my State, it would fired when I do set value from State, but not from Binding, for this reason I have to give a didSet to Binding這個 State，這對我來說不合邏輯，綁定應該綁定，但它使用更新 State 的優勢創建了該值的自己版本，我在徘徊，如果它是一個錯誤，或者它應該以這種方式，我的意思是我我期待在狀態綁定方面的引用類型行為，但是使用這個向下代碼？ 它顯示更像值類型！ 為什么會這樣？ 我期待 State 的 didSet 即使來自 Binding 的更新也會被解雇！

    import SwiftUI

struct ContentView: View {
    
    @State var someProperty: String = "Empty string!" {
        
        didSet(oldValue) {
            
            print("State didSet → " + someProperty)
            
        }
    }
    
    var body: some View {
        
        Text(someProperty)
            .padding()
        
        ButtonView(someProperty: $someProperty)
        
    }
}


struct ButtonView: View {
    
    @Binding var someProperty: String  {
        
        didSet(oldValue) {
            
            print("Binding didSet → " + someProperty)
            
        }
    }
    
    var body: some View {
        
        Button("update Text") { someProperty = "Hello, world!" }
        
    }
}

---

更新：

    struct ContentView: View {

    @State private var someProperty: String = "Empty string!" {

        didSet(oldValue) {

            print("State didSet → " + someProperty)

        }
    }

    var body: some View {

        Text(someProperty)
            .padding()

        Button("update Text") { someProperty = "Hello, world!" }


    }
}

Answer 1

使用自定義綁定

var body: some View {
    
    Text(someProperty)
        .padding()
    
    ButtonView(someProperty: Binding(
        get: { self.someProperty },
        set: { self.someProperty = $0 }
    ))
    
}

Answer 2

didSet僅在您直接修改@State而不是在您更改其內部值時才與@State一起使用。

請注意， State是一個包裝器。 如果您使用Binding更改其內部值（此處_someProperty ），則不會調用didSet 。

您可以使用onReceive或onChange代替：

import Combine
import SwiftUI

struct ContentView: View {
    @State private var someProperty: String = "Empty string!"

    var body: some View {
        Text(someProperty)
            .padding()
            // updated on changes only
            .onChange(of: someProperty) {
                print("State onChange → " + $0)
            }
            // updated every time
            .onReceive(Just(someProperty)) {
                print("State onReceive → " + $0)
            }

        ButtonView(someProperty: $someProperty)
    }
}