当变量嵌套在对象中时，如何使用 SwiftUI 将绑定传递给子视图？

Question

这个有效

import SwiftUI
struct ContentView : View {
    @State var val1: Int = 0
    var body: some View {
        MySubview(val1: $val1)
    }
}

#if DEBUG
struct ContentView_Previews : PreviewProvider {
    static var previews: some View {
        ContentView(val1: 0)
    }
}
#endif

struct MySubview : View {
    @Binding var val1: Int
    var body: some View {
        return Text("Value = \(val1)")
    }
}

但是当变量嵌套在对象中时，这会失败

import SwiftUI
struct MyStruct {
    let number: Int
}

struct ContentView : View {
    @State var val1 = MyStruct(number: 7)
    var body: some View {
        MySubview(val1: $val1.number)
    }
}

#if DEBUG
struct ContentView_Previews : PreviewProvider {
    static var previews: some View {
        ContentView(val1: 0)
    }
}
#endif

struct MySubview : View {
    @Binding var val1: Int
    var body: some View {
        return Text("Value = \(val1)")
    }
}

显示错误：Generic parameter 'Subject' could not be inferred

如何将嵌套变量作为绑定传递给子视图？

Answer 1

该错误具有很强的误导性。数字必须是 var，而不是 let:

struct MyStruct {
    var number: Int
}

改一下就可以了。

Answer 2

你的代码很好，除了需要 var number: Int 正如 kontiki 指出的那样。

为了帮助理解在视图之间传递绑定，我准备了以下代码，它以稍微不同的方式显示了 @Binding 的使用：

import SwiftUI

struct Zoo    { var shed:    Shed     }
struct Shed   { var animals: [Animal] }
struct Animal { var legs:    Int      }

struct ZooView : View {
  @State var zoo = Zoo( shed: Shed(animals:
      [ Animal(legs: 2), Animal(legs: 4) ] ) )

  var body: some View {
    VStack {
      Text("Legs in the zoo directly:")
      Text("Animal 1 Legs: \(zoo.shed.animals[0].legs)")
      Text("Animal 2 Legs: \(zoo.shed.animals[1].legs)")
      Divider()
      Text("And now with nested views:")
      ShedView(shed: $zoo.shed)
    }
  }
}

struct ShedView : View {
  @Binding var shed: Shed

  var body: some View {
    ForEach(shed.animals.indices) { index in
      VStack {
        Text("Animal: \(index+1)")
        AnimalView(animal: self.$shed.animals[index])
      }
    }
  }
}

struct AnimalView : View {
  @Binding var animal: Animal

  var body: some View {
    VStack {
      Text("Legs = \(animal.legs)")
      Button(
      action: { self.animal.legs += 1 }) {
        Text("Another leg")
      }
    }
  }
}

特别是 ShedView 被赋予一个棚屋的绑定，它在棚屋中的动物数组中查找一个动物，并将对该动物的绑定传递给 AnimalView。

当变量嵌套在对象中时，如何使用 SwiftUI 将绑定传递给子视图？

How to pass binding to subview with SwiftUI when the variable is nested in an object?

swift

swiftui