SwiftUI TabView: Set selected tabItem from different view but detecting repeated selection - button

Question

I'd like to display a TabView to display different screens. My first screen (home) displays three buttons which can select one of the three screens to display.
But(!) I have to check if a tab is repeatedly selected to trigger in this case a special action.
The detection of the repeatedly selection for screen2 works fine but then I'm not able to set a selection by the buttons.
I've tried to use an #EnvironmentalObject but changes to this object are not observed in my TabView.selection.
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

You need to make appState observed and you don't need selection at all (it is just a duplicate).
I've put everything into separated ContentView (to leave scene for scene only)
Tested with Xcode 12 / iOS 14
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)
}
}
}
}