swift - 如何在 swiftui 中强制 View 更新 onAppear

Question

是否可以在Appear上查看内容 View ？该方法被调用，但列表未更新 似乎应该有某种方法来做到这一点

import SwiftUI

var texts = ["0", "0", "0"]

struct ContentView: View {


  var body: some View {
      List {
        Text(texts[0])
        Text(texts[1])
        Text(texts[2])

      }
      .onAppear(){
        texts[0] = "1"
        print(texts)
    }
    }
}

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

Answer 1

如果你想重新渲染，你需要使用状态。

如果将 texts 变量带入 ContentView 结构并将其声明为 @State 那么它将导致 ContentView 重新渲染。

请注意，当您在闭包中引用texts时，您必须在onAppear中使用self。

struct ContentView: View {

  @State private var texts = ["0", "0", "0"] . // Apple suggests that these should be private

  var body: some View {
      List {
        Text(texts[0])
        Text(texts[1])
        Text(texts[2])

      }
      .onAppear(){
        self.texts[0] = "1"
        print(self.texts)
      }
    }
}

<小时/>

但是，如果您想在多个 View 之间共享文本，那么您将需要创建一个环境对象。您可以按如下方式执行此操作:

创建一个 ObservableObject。

class Texts: ObservableObject {
    @Published var texts = ["0", "0", "0"] // You can obviously choose whichever name you want for this variable.
}

然后在您的 SceneDelegate 中创建该对象的实例并将其附加到您的 ContentView。

let texts = Texts()
let contentView = ContentView().environmentObject(texts)

然后在 ContentView.swift 中你可以像这样使用它:

struct ContentView: View {

  @EnvironmentObject var texts: Texts

  var body: some View {
      List {
        // notice that you have to access the texts array that is stored in texts object
        Text(texts.texts[0])
        Text(texts.texts[1])
        Text(texts.texts[2])

      }
      .onAppear(){
        self.texts.texts[0] = "1"
        print(self.texts.texts)
       }
    }
}

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