Question

我想显示一个TabView来显示不同的屏幕。我的第一个屏幕（主页）显示三个按钮，可以选择三个屏幕中的一个进行显示。但是（！）我必须检查是否重复选择了一个选项卡以在这种情况下触发特殊动作。

检测到screen2的重复选择效果很好，但是我无法通过按钮设置选择。我尝试使用@EnvironmentalObject，但是在TabView.selection中未观察到对此对象的更改。

   import SwiftUI

   @main
   struct TestApp: App {
       static let kIndex0 = 0
       static let kIndex1 = 1
       static let kIndex2 = 2

       var appState = AppState()

       @State private var selection = TestApp.kIndex0

       var body: some Scene {
           // this code is required to detect a repeated selection of
           // the same tab to trigger a special action
           let index = Binding<Int>(
               get: { self.selection },
               set: {
                   if $0 == TestApp.kIndex1  &&  self.selection == $0 {
                       print("Trigger special action for index 1")
                   }
                   print("Pressed tab: \($0)  self.selction: \(self.selection)  app.selectedTab: \(appState.selectedTab)")

                   self.selection = $0
                   appState.selectedTab = $0
               })

           WindowGroup {
               TabView(selection: index) {
                   First()
                       .environmentObject(appState)
                      .tabItem {
                           Image(systemName: "1.circle")
                           Text("Home")
                       }.tag(TestApp.kIndex0)
                
                   Text("Second Content View")
                       .tabItem {
                           Image(systemName: "2.circle")
                           Text("Screen Two")
                       }.tag(TestApp.kIndex1)

                   Text("Third Content View")
                       .tabItem {
                           Image(systemName: "3.circle")
                           Text("Screen Three")
                       }.tag(TestApp.kIndex2)
               }
           }
       }
   }


   class AppState: ObservableObject {
       @Published var selectedTab = TestApp.kIndex0
   }


   /*
       Place to buttons which should select on of the the two
       tabs of TestUI
    */
   struct First: View {
       @EnvironmentObject var appState: AppState

       var body: some View {
           VStack(alignment: .leading, spacing: 20) {
               AButton(tabIndex: TestApp.kIndex0, iconName: "1.circle", text: "This first screen")
                   .environmentObject(appState)

               AButton(tabIndex: TestApp.kIndex1, iconName: "2.circle", text: "Second screen")
                   .environmentObject(appState)

                  AButton(tabIndex: TestApp.kIndex1, iconName: "3.circle", text: "Third screen")
                   .environmentObject(appState)
           }
       }
   }


   struct AButton: View {
       let tabIndex: Int
       let iconName: String
       let text: String

       @EnvironmentObject var appState: AppState

       var body: some View {
           Button(action: {
               appState.selectedTab = tabIndex
           }) {
               HStack() {
                   Image(systemName: iconName)
                       .imageScale(.large)
                       .frame(minWidth: 50)
                   Text(text)
               }
           }
       }
   }

Answer 1

您需要观察appState，而根本不需要selection（只是重复）。

我已将所有内容放在单独的ContentView中（仅将场景留在场景中）

通过Xcode 12 / iOS 14测试

struct ContentView: View {

    @StateObject var appState = AppState()

    var body: some View {
        // this code is required to detect a repeated selection of
        // the same tab to trigger a special action
        let index = Binding<Int>(
            get: { self.appState.selectedTab },
            set: {
                if $0 == TestApp.kIndex1  &&  self.appState.selectedTab == $0 {
                    print("Trigger special action for index 1")
                }
                print("Pressed tab: \($0) app.selectedTab: \(appState.selectedTab)")
                appState.selectedTab = $0
            })

        TabView(selection: index) {
            First()
                .environmentObject(appState)
                .tabItem {
                    Image(systemName: "1.circle")
                    Text("Home")
                }.tag(TestApp.kIndex0)

            Text("Second Content View")
                .tabItem {
                    Image(systemName: "2.circle")
                    Text("Screen Two")
                }.tag(TestApp.kIndex1)

            Text("Third Content View")
                .tabItem {
                    Image(systemName: "3.circle")
                    Text("Screen Three")
                }.tag(TestApp.kIndex2)
        }
    }
}


class AppState: ObservableObject {
    @Published var selectedTab = TestApp.kIndex0
}


struct First: View {
    @EnvironmentObject var appState: AppState

    var body: some View {
        VStack(alignment: .leading, spacing: 20) {
            AButton(tabIndex: TestApp.kIndex0, iconName: "1.circle", text: "This first screen")

            AButton(tabIndex: TestApp.kIndex1, iconName: "2.circle", text: "Second screen")

            AButton(tabIndex: TestApp.kIndex2, iconName: "3.circle", text: "Third screen")
        }
    }
}


struct AButton: View {
    let tabIndex: Int
    let iconName: String
    let text: String

    @EnvironmentObject var appState: AppState

    var body: some View {
        Button(action: {
            appState.selectedTab = tabIndex
        }) {
            HStack() {
                Image(systemName: iconName)
                    .imageScale(.large)
                    .frame(minWidth: 50)
                Text(text)
            }
        }
    }
}

SwiftUI TabView：从其他视图设置选定的tabItem，但检测到重复的选择

1 个答案: