在SwiftUI中的ForEach TextField

Question

假设我有一个名为 Student 的类。

class Student: Identifiable, ObservableObject {
    var id = UUID()

    @Published var name = ""
}

在另一个类（称为Class）的数组中使用。

class Class: Identifiable, ObservableObject {
    var id = UUID()

    @Published var name = ""
    var students = [Student()]
}

在我的View中，它的定义如下。

@ObservedObject var newClass = Class()

我的问题是：我如何为每个学生创建一个TextField，并正确地将其与name属性绑定（避免出现错误）？

ForEach(self.newClass.students) { student in
    TextField("Name", text: student.name)
}

现在，Xcode 抛出了这个错误:

Cannot convert value of type 'TextField<Text>' to closure result type '_'

我尝试在调用变量之前添加一些$，但似乎并没有起作用。

- João Gabriel

Answer 1

只需将学生姓名属性的@Published更改为@State。 @State是提供带有$前缀的Binding的属性。

import SwiftUI

class Student: Identifiable, ObservableObject {
  var id = UUID()

  @State var name = ""
}

class Class: Identifiable, ObservableObject {
  var id = UUID()

  @Published var name = ""
  var students = [Student()]
}

struct ContentView: View {
  @ObservedObject var newClass = Class()

  var body: some View {
    Form {
      ForEach(self.newClass.students) { student in
        TextField("Name", text: student.$name) // note the $name here
      }
    }
  }
}

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

一般来说，我建议使用结构体而不是类。

struct Student: Identifiable {
  var id = UUID()
  @State var name = ""
}

struct Class: Identifiable {
  var id = UUID()

  var name = ""
  var students = [
    Student(name: "Yo"),
    Student(name: "Ya"),
  ]
}

struct ContentView: View {
  @State private var newClass = Class()

  var body: some View {
    Form {
      ForEach(self.newClass.students) { student in
        TextField("Name", text: student.$name)
      }
    }
  }
}

- Kevin Renskers

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Xcode 13 给我关于这个的警告：“在视图上安装之外访问状态的值。这将导致初始值的常量绑定，并且不会更新。” - Cocoanetics