SwiftUI: Pop to root view when selected tab is tapped again - swift

Question

Starting point is a NavigationView within a TabView. I'm struggling with finding a SwiftUI solution to pop to the root view within the navigation stack when the selected tab is tapped again. In the pre-SwiftUI times, this was as simple as the following:
func tabBarController(_ tabBarController: UITabBarController, didSelect viewController: UIViewController) {
let navController = viewController as! UINavigationController
navController.popViewController(animated: true)
}
Do you know how the same thing can be achieved in SwiftUI?
Currently, I use the following workaround that relies on UIKit:
if let windowScene = scene as? UIWindowScene {
let window = UIWindow(windowScene: windowScene)
let navigationController = UINavigationController(rootViewController: UIHostingController(rootView: MyCustomView() // -> this is a normal SwiftUI file
.environment(\.managedObjectContext, context)))
navigationController.tabBarItem = UITabBarItem(title: "My View 1", image: nil, selectedImage: nil)
// add more controllers that are part of tab bar controller
let tabBarController = UITabBarController()
tabBarController.viewControllers = [navigationController /* , additional controllers */ ]
window.rootViewController = tabBarController // UIHostingController(rootView: contentView)
self.window = window
window.makeKeyAndVisible()
}

Answer 1

Here is possible approach. For TabView it gives the same behaviour as tapping to the another tab and back, so gives persistent look & feel.
Tested & works with Xcode 11.2 / iOS 13.2
Full module code:
import SwiftUI
struct TestPopToRootInTab: View {
#State private var selection = 0
#State private var resetNavigationID = UUID()
var body: some View {
let selectable = Binding( // << proxy binding to catch tab tap
get: { self.selection },
set: { self.selection = $0
// set new ID to recreate NavigationView, so put it
// in root state, same as is on change tab and back
self.resetNavigationID = UUID()
})
return TabView(selection: selectable) {
self.tab1()
.tabItem {
Image(systemName: "1.circle")
}.tag(0)
self.tab2()
.tabItem {
Image(systemName: "2.circle")
}.tag(1)
}
}
private func tab1() -> some View {
NavigationView {
NavigationLink(destination: TabChildView()) {
Text("Tab1 - Initial")
}
}.id(self.resetNavigationID) // << making id modifiable
}
private func tab2() -> some View {
Text("Tab2")
}
}
struct TabChildView: View {
var number = 1
var body: some View {
NavigationLink("Child \(number)",
destination: TabChildView(number: number + 1))
}
}
struct TestPopToRootInTab_Previews: PreviewProvider {
static var previews: some View {
TestPopToRootInTab()
}
}

Answer 2

Here's an approach that uses a PassthroughSubject to notify the child view whenever the tab is re-selected, and a view modifier to allow you to attach .onReselect() to a view.
import SwiftUI
import Combine
enum TabSelection: String {
case A, B, C // etc
}
private struct DidReselectTabKey: EnvironmentKey {
static let defaultValue: AnyPublisher<TabSelection, Never> = Just(.Mood).eraseToAnyPublisher()
}
private struct CurrentTabSelection: EnvironmentKey {
static let defaultValue: Binding<TabSelection> = .constant(.Mood)
}
private extension EnvironmentValues {
var tabSelection: Binding<TabSelection> {
get {
return self[CurrentTabSelection.self]
}
set {
self[CurrentTabSelection.self] = newValue
}
}
var didReselectTab: AnyPublisher<TabSelection, Never> {
get {
return self[DidReselectTabKey.self]
}
set {
self[DidReselectTabKey.self] = newValue
}
}
}
private struct ReselectTabViewModifier: ViewModifier {
#Environment(\.didReselectTab) private var didReselectTab
#State var isVisible = false
let action: (() -> Void)?
init(perform action: (() -> Void)? = nil) {
self.action = action
}
func body(content: Content) -> some View {
content
.onAppear {
self.isVisible = true
}.onDisappear {
self.isVisible = false
}.onReceive(didReselectTab) { _ in
if self.isVisible, let action = self.action {
action()
}
}
}
}
extension View {
public func onReselect(perform action: (() -> Void)? = nil) -> some View {
return self.modifier(ReselectTabViewModifier(perform: action))
}
}
struct NavigableTabViewItem<Content: View>: View {
#Environment(\.didReselectTab) var didReselectTab
let tabSelection: TabSelection
let imageName: String
let content: Content
init(tabSelection: TabSelection, imageName: String, #ViewBuilder content: () -> Content) {
self.tabSelection = tabSelection
self.imageName = imageName
self.content = content()
}
var body: some View {
let didReselectThisTab = didReselectTab.filter( { $0 == tabSelection }).eraseToAnyPublisher()
NavigationView {
self.content
.navigationBarTitle(tabSelection.localizedStringKey, displayMode: .inline)
}.tabItem {
Image(systemName: imageName)
Text(tabSelection.localizedStringKey)
}
.tag(tabSelection)
.navigationViewStyle(StackNavigationViewStyle())
.keyboardShortcut(tabSelection.keyboardShortcut)
.environment(\.didReselectTab, didReselectThisTab)
}
}
struct NavigableTabView<Content: View>: View {
#State private var didReselectTab = PassthroughSubject<TabSelection, Never>()
#State private var _selection: TabSelection = .Mood
let content: Content
init(#ViewBuilder content: () -> Content) {
self.content = content()
}
var body: some View {
let selection = Binding(get: { self._selection },
set: {
if self._selection == $0 {
didReselectTab.send($0)
}
self._selection = $0
})
TabView(selection: selection) {
self.content
.environment(\.tabSelection, selection)
.environment(\.didReselectTab, didReselectTab.eraseToAnyPublisher())
}
}
}

Answer 3

Here's how I did it:
struct UIKitTabView: View {
var viewControllers: [UIHostingController<AnyView>]
init(_ tabs: [Tab]) {
self.viewControllers = tabs.map {
let host = UIHostingController(rootView: $0.view)
host.tabBarItem = $0.barItem
return host
}
}
var body: some View {
TabBarController(controllers: viewControllers).edgesIgnoringSafeArea(.all)
}
struct Tab {
var view: AnyView
var barItem: UITabBarItem
init<V: View>(view: V, barItem: UITabBarItem) {
self.view = AnyView(view)
self.barItem = barItem
}
}
}
struct TabBarController: UIViewControllerRepresentable {
var controllers: [UIViewController]
func makeUIViewController(context: Context) -> UITabBarController {
let tabBarController = UITabBarController()
tabBarController.viewControllers = controllers
tabBarController.delegate = context.coordinator
return tabBarController
}
func updateUIViewController(_ uiViewController: UITabBarController, context: Context) { }
}
extension TabBarController {
func makeCoordinator() -> TabBarController.Coordinator {
Coordinator(self)
}
class Coordinator: NSObject, UITabBarControllerDelegate {
var parent: TabBarController
init(_ parent: TabBarController){self.parent = parent}
var previousController: UIViewController?
private var shouldSelectIndex = -1
func tabBarController(_ tabBarController: UITabBarController, shouldSelect viewController: UIViewController) -> Bool {
shouldSelectIndex = tabBarController.selectedIndex
return true
}
func tabBarController(_ tabBarController: UITabBarController, didSelect viewController: UIViewController) {
if shouldSelectIndex == tabBarController.selectedIndex {
if let navVC = tabBarController.viewControllers![shouldSelectIndex].nearestNavigationController {
if (!(navVC.popViewController(animated: true) != nil)) {
navVC.viewControllers.first!.scrollToTop()
}
}
}
}
}
}
extension UIViewController {
var nearestNavigationController: UINavigationController? {
if let selfTypeCast = self as? UINavigationController {
return selfTypeCast
}
if children.isEmpty {
return nil
}
for child in self.children {
return child.nearestNavigationController
}
return nil
}
}
extension UIViewController {
func scrollToTop() {
func scrollToTop(view: UIView?) {
guard let view = view else { return }
switch view {
case let scrollView as UIScrollView:
if scrollView.scrollsToTop == true {
scrollView.setContentOffset(CGPoint(x: 0.0, y: -scrollView.safeAreaInsets.top), animated: true)
return
}
default:
break
}
for subView in view.subviews {
scrollToTop(view: subView)
}
}
scrollToTop(view: view)
}
}
Then in ContentView.swift I use it like this:
struct ContentView: View {
var body: some View {
ZStack{
UIKitTabView([
UIKitTabView.Tab(
view: FirstView().edgesIgnoringSafeArea(.top),
barItem: UITabBarItem(title: "Tab1", image: UIImage(systemName: "star"), selectedImage: UIImage(systemName: "star.fill"))
),
UIKitTabView.Tab(
view: SecondView().edgesIgnoringSafeArea(.top),
barItem: UITabBarItem(title: "Tab2", image: UIImage(systemName: "star"), selectedImage: UIImage(systemName: "star.fill"))
),
])
}
}
}
Note that when the user is already on the root view, it scrolls to top automatically

Answer 4

Here's what I did with introspect swiftUI library.
https://github.com/siteline/SwiftUI-Introspect
struct TabBar: View {
#State var tabSelected: Int = 0
#State var navBarOne: UINavigationController?
#State var navBarTwo: UINavigationController?
#State var navBarThree: UINavigationController?
var body: some View {
return TabView(selection: $tabSelected){
NavView(navigationView: $navBarOne).tabItem {
Label("Home1",systemImage: "bag.fill")
}.tag(0)
NavView(navigationView: $navBarTwo).tabItem {
Label("Orders",systemImage: "scroll.fill" )
}.tag(1)
NavView(navigationView: $navBarThree).tabItem {
Label("Wallet", systemImage: "dollarsign.square.fill" )
// Image(systemName: tabSelected == 2 ? "dollarsign.square.fill" : "dollarsign.square")
}.tag(2)
}.onTapGesture(count: 2) {
switch tabSelected{
case 0:
self.navBarOne?.popToRootViewController(animated: true)
case 1:
self.navBarTwo?.popToRootViewController(animated: true)
case 2:
self.navBarThree?.popToRootViewController(animated: true)
default:
print("tapped")
}
}
}
}
NavView:
import SwiftUI
import Introspect
struct NavView: View {
#Binding var navigationView: UINavigationController?
var body: some View {
NavigationView{
VStack{
NavigationLink(destination: Text("Detail view")) {
Text("Go To detail")
}
}.introspectNavigationController { navController in
navigationView = navController
}
}
}
}
This actually isn't the best approach because it makes the entire tab view and everything inside of it have the double-tap gesture which would pop the view to its root. My current fix for this allows for one tap to pop up root view haven't figured out how to add double tap
struct TabBar: View {
#State var tabSelected: Int = 0
#State var navBarOne: UINavigationController?
#State var navBarTwo: UINavigationController?
#State var navBarThree: UINavigationController?
#State var selectedIndex:Int = 0
var selectionBinding: Binding<Int> { Binding(
get: {
self.selectedIndex
},
set: {
if $0 == self.selectedIndex {
popToRootView(tabSelected: $0)
}
self.selectedIndex = $0
}
)}
var body: some View {
return TabView(selection: $tabSelected){
NavView(navigationView: $navBarOne).tabItem {
Label("Home1",systemImage: "bag.fill")
}.tag(0)
NavView(navigationView: $navBarTwo).tabItem {
Label("Orders",systemImage: "scroll.fill" )
}.tag(1)
NavView(navigationView: $navBarThree).tabItem {
Label("Wallet", systemImage: "dollarsign.square.fill" )
// Image(systemName: tabSelected == 2 ? "dollarsign.square.fill" : "dollarsign.square")
}.tag(2)
}
}
func popToRootView(tabSelected: Int){
switch tabSelected{
case 0:
self.navBarOne?.popToRootViewController(animated: true)
case 1:
self.navBarTwo?.popToRootViewController(animated: true)
case 2:
self.navBarThree?.popToRootViewController(animated: true)
default:
print("tapped")
}
}
}

Answer 5

I took an approach similar to Asperi
Use a combination of a custom binding, and a separately stored app state var for keeping state of the navigation link.
The custom binding allows you to see all taps basically even when the current tab is the one thats tapped, something that onChange of tab selection binding doesn't show. This is what imitates the UIKit TabViewDelegate behavior.
This doesn't require a "double tap", if you just a single tap of the current, if you want double tap you'll need to implement your own tap/time tracking but shouldn't be too hard.
class AppState: ObservableObject {
#Published var mainViewShowingDetailView = false
}
struct ContentView: View {
#State var tabState: Int = 0
#StateObject var appState = AppState()
var body: some View {
let binding = Binding<Int>(get: { tabState },
set: { newValue in
if newValue == tabState { // tapped same tab they're already on
switch newValue {
case 0: appState.mainViewShowingDetailView = false
default: break
}
}
tabState = newValue // make sure you actually set the storage
})
TabView(selection: binding) {
MainView()
.tabItem({ Label("Home", systemImage: "list.dash") })
.tag(0)
.environmentObject(appState)
}
}
}
struct MainView: View {
#EnvironmentObject var appState: AppState
var body: {
NavigationView {
VStack {
Text("Hello World")
NavigationLink(destination: DetailView(),
isActive: $appState.mainViewShowingDetailView,
label: { Text("Show Detail") })
}
}
}
}
struct DetailView: View {
...
}

Answer 6

iOS 16 / NavigationStack approach with PassthroughSubject
Uses willSet on selectedTab to get the tap event, and uses a PassthroughSubject for sending the event to the children. This is picked up by the .onReceived and calls a function for popping the views from the NavigationStack
Did a full write up here: https://kentrobin.com/home/tap-tab-to-go-back/ and created a working demo project here: https://github.com/kentrh/demo-tap-tab-to-go-back
class HomeViewModel: ObservableObject {
#Published var selectedTab: Tab = .tab1 {
willSet {
if selectedTab == newValue {
subject.send(newValue)
}
}
}
let subject = PassthroughSubject<Tab, Never>()
enum Tab: Int {
case tab1 = 0
}
}
struct HomeView: View {
#StateObject var viewModel: HomeViewModel = .init()
var body: some View {
TabView(selection: $viewModel.selectedTab) {
Tab1View(subject: viewModel.subject)
.tag(HomeViewModel.Tab.tab1)
.tabItem {
Label("Tab 1", systemImage: "1.lane")
Text("Tab 1", comment: "Tab bar title")
}
}
}
}
struct Tab1View: View {
#StateObject var viewModel: Tab1ViewModel = .init()
let subject: PassthroughSubject<HomeViewModel.Tab, Never>
var body: some View {
NavigationStack(path: $viewModel.path) {
List {
NavigationLink(value: Tab1ViewModel.Route.viewOne("From tab 1")) {
Text("Go deeper to OneView")
}
NavigationLink(value: Tab1ViewModel.Route.viewTwo("From tab 1")) {
Text("Go deeper to TwoView")
}
}
.navigationTitle("Tab 1")
.navigationDestination(for: Tab1ViewModel.Route.self, destination: { route in
switch route {
case let .viewOne(text):
Text(text)
case let .viewTwo(text):
Text(text)
}
})
.onReceive(subject) { tab in
if case .tab1 = tab { viewModel.tabBarTapped() }
}
}
}
}
class Tab1ViewModel: ObservableObject {
#Published var path: [Route] = []
func tabBarTapped() {
if path.count > 0 {
path.removeAll()
}
}
enum Route: Hashable {
case viewOne(String)
case viewTwo(String)
}
}