FB13103224: SwiftUI.TabView's tab useless onAppear call occurs when TabView is removed

[Yoshinori Imajo]

• Date: 2023-09-02
• Resolution: Open
• Area: SwiftUI
• OS: iOS 17 beta 8
• Type: incorrect/Unexpected Behavior
• Keywords:

Details

Description

When SwiftUI.TabView is removed from the View, each Tab unnecessarily calls .onAppear.

Condition. There must be multiple tabs, and each of the multiple tabs must be visible at least once. Specifically, this occurs when the Home screen is displayed in the TabView, and the tab is destroyed by logging out after switching to the profile screen.

import SwiftUI

struct ContentView: View {
    @State var loggedIn: Bool = false

    var body: some View {
        switch loggedIn {
        case false:
            Button("Login") {
                loggedIn = true
            }
        case true:
            TabView {
                NavigationView {
                    Text("Home")
                        .navigationBarTitle("Home")
                }
                .tabItem {
                    Image(systemName: "house")
                    Text("Home")
                }
                .onAppear {
                    print("🍏 Home on appear 💢💢💢💢")
                }
                .onDisappear {
                    print("🍎 Home on disappear")
                }

                NavigationView {
                    Text("Profile")
                        .navigationBarTitle("Profile")
                        .toolbar {
                            ToolbarItem(placement: .navigationBarTrailing) {
                                Button("Logout") {
                                    loggedIn = false
                                }
                            }
                        }
                }
                .tabItem {
                    Image(systemName: "person")
                    Text("Profile")
                }
                .onAppear {
                    print("🍏 Profile on appear")
                }
                .onDisappear {
                    print("🍎 Profile on disappear")
                }
            }
        }
    }
}

Actual logs...

🍏 Home on appear 💢💢💢💢
🍏 Profile on appear
🍎 Home on disappear
🍏 Home on appear 💢💢💢💢
🍎 Home on disappear
🍎 Profile on disappear

Expected Logs...

🍏 Home on appear 💢💢💢💢
🍏 Profile on appear
🍎 Home on disappear
🍎 Profile on disappear

This is true not only for onAppear but also for task.

Please refer to the Developer Forum for more information.
https://developer.apple.com/forums/thread/719521?login=true

Files