When using NavigationLink on the bottom of a view after ForEach it won't work if it is not visible.
I have a list of Buttons. If a button is pressed, it sets a Bool to true. This bool value now shows a NavigationLink which immediately activates because the passed binding is set to true.
However, the link won't work if the array is too long because it will be out of sight once one of the first buttons is pressed.
This is my Code:
import SwiftUI
struct TestLinkView: View {
#State private var linkIsActive = false
var body: some View {
NavigationView {
VStack {
Button(action: {
linkIsActive = true
}) {
Text("Press")
}
NavigationLink(destination: ListView(linkIsActive: $linkIsActive), isActive: $linkIsActive) {
Text("Navigation Link")
}
}
}
}
}
struct ListView: View {
var nameArray = ["Name1","Name2","Name3","Name4","Name5","Name6","Name7","Name8","Name9","Name10","Name11","Name12","Name13","Name14","Name15","Name16","Name17","Name18","Name19","Name20" ]
#State private var showLink: Bool = false
#State private var selectedName: String = ""
#Binding var linkIsActive: Bool
var body: some View {
Form {
ForEach(nameArray, id: \.self) { name in
Button(action: {
selectedName = name
showLink = true
}) {
Text(name)
}
}
if showLink {
NavigationLink(destination: NameView(selectedName: selectedName), isActive: $linkIsActive) {
EmptyView()
}
}
}
.navigationBarTitle("ListView")
}
}
struct NameView: View {
var selectedName: String
var body: some View {
Text(selectedName)
.navigationBarTitle("NameView")
}
}
What would work is to pass the NavigationLink with the if-condition inside the button label. However if I do that, the animation won't work anymore.
You don't need it in Form, which is like a List don't create views far outside of visible area. In your case the solution is to just move link into background of Form (because it does not depend on form internals).
The following tested as worked with Xcode 12 / iOS 14.
Form {
ForEach(nameArray, id: \.self) { name in
Button(action: {
selectedName = name
showLink = true
}) {
Text(name)
}
}
}
.background(Group{
if showLink {
NavigationLink(destination: NameView(selectedName: selectedName), isActive: $linkIsActive) {
EmptyView()
}
}
})
Related
I am trying to implement the behavior in a TabView when the user taps the same tab multiple times, such as in the iOS AppStore app. First tap: switch to that view, second tap: pop to root, third tap: scroll to the top if needed.
The code below works fine for switching and didTap() is called for every tap.
import SwiftUI
enum Tab: String {
case one
case two
}
struct AppView: View {
#State private var activeTab = Tab.one
var body: some View {
TabView(selection: $activeTab.onChange(didTap)) {
One()
.tabItem {
Label("one", systemImage: "1.lane")
}
.tag(Tab.one)
Two()
.tabItem {
Label("two", systemImage: "2.lane")
}
.tag(Tab.two)
}
}
func didTap(to value: Tab) {
print(value) // this captures every tap
}
}
extension Binding {
func onChange(_ handler: #escaping (Value) -> Void) -> Binding<Value> {
Binding(
get: { self.wrappedValue },
set: { newValue in
self.wrappedValue = newValue
handler(newValue)
}
)
}
}
What I am struggling with, is how to tell either One or Two that it was tapped for a second or third time? (How to pop and scroll is not the issue).
I have seen this: TabView, tabItem: running code on selection or adding an onTapGesture but it doesn't explain how to run code in one of the views.
Any suggestions?
You can record additional taps (of same value) in an array. The array count gives you the number of taps on the same Tab.
EDIT: now with explicit subview struct.
struct ContentView: View {
#State private var activeTab = Tab.one
#State private var tapState: [Tab] = [Tab.one] // because .one is default
var body: some View {
TabView(selection: $activeTab.onChange(didTap)) {
SubView(title: "One", tapCount: tapState.count)
.tabItem {
Label("one", systemImage: "1.lane")
}
.tag(Tab.one)
SubView(title: "Two", tapCount: tapState.count)
.tabItem {
Label("two", systemImage: "2.lane")
}
.tag(Tab.two)
}
}
func didTap(to value: Tab) {
print(value) // this captures every tap
if tapState.last == value {
tapState.append(value) // apped next tap if same value
print("tapped \(tapState.count) times")
} else {
tapState = [value] // reset tap state to new tab selection
}
}
}
struct SubView: View {
let title: String
let tapCount: Int
var body: some View {
VStack {
Text("Subview \(title)").font(.title)
Text("tapped \(tapCount) times")
}
}
}
Although the answer by #ChrisR did answer my question, I couldn't figure out the next step, i.e. the logic when to pop-to-root or scroll-to-the-top based on the number of taps for a SubView. After lots of reading and trial and error, I recently came across this article: https://notificare.com/blog/2022/11/25/a-better-tabview-in-swiftui/
Inspired by this article, but with some modifications, I came up with the following which does exactly what I was looking for.
The two main changes are:
An EmptyView with an id is added as the first (but invisible) row in the List to be used as an anchor by proxy.scrollTo().
Instead of the global #StateObject var appState that stores the navigation paths for the subviews, I added the paths as separate #State properties. This avoids the Update NavigationAuthority bound path tried to update multiple times per frame. warning.
Hopefully this is helpful for someone.
enum Tab: String {
case one
case two
}
struct ContentView: View {
#State var selectedTab = Tab.one
#State var oneNavigationPath = NavigationPath()
#State var twoNavigationPath = NavigationPath()
var body: some View {
ScrollViewReader { proxy in
TabView(selection: tabViewSelectionBinding(proxy: proxy)) {
SubView(title: "One", path: $oneNavigationPath)
.tabItem {
Label("one", systemImage: "1.lane")
}
.tag(Tab.one)
SubView(title: "Two", path: $twoNavigationPath)
.tabItem {
Label("two", systemImage: "2.lane")
}
.tag(Tab.two)
}
}
}
private func tabViewSelectionBinding(proxy: ScrollViewProxy) -> Binding<Tab> {
Binding<Tab>(
get: { selectedTab },
set: { newValue in
if selectedTab == newValue {
switch selectedTab {
case .one:
if oneNavigationPath.isEmpty {
withAnimation {
proxy.scrollTo(Tab.one, anchor: .bottom)
}
} else {
withAnimation {
oneNavigationPath = NavigationPath()
}
}
case .two:
if twoNavigationPath.isEmpty {
withAnimation {
proxy.scrollTo(Tab.two, anchor: .bottom)
}
} else {
withAnimation {
twoNavigationPath = NavigationPath()
}
}
}
}
selectedTab = newValue
}
)
}
}
struct SubView: View {
let title: String
let items = Array(1 ... 100)
#Binding var path: NavigationPath
var body: some View {
NavigationStack(path: $path) {
List {
EmptyView()
.id(Tab(rawValue: title.lowercased()))
ForEach(items, id: \.self) { item in
NavigationLink(value: item) {
Text("Item \(item)")
}
}
}
.navigationTitle(title)
.navigationDestination(for: Int.self) { item in
Text("Item \(item)")
}
}
}
}
Here is a simple list view of "Topic" struct items. The goal is to present an editor view when a row of the list is tapped. In this code, tapping a row is expected to cause the selected topic to be stored as "tappedTopic" in an #State var and sets a Boolean #State var that causes the EditorV to be presented.
When the code as shown is run and a line is tapped, its topic name prints properly in the Print statement in the Button action, but then the app crashes because self.tappedTopic! finds tappedTopic to be nil in the EditTopicV(...) line.
If the line "tlVM.objectWillChange.send()" is uncommented, the code runs fine. Why is this needed?
And a second puzzle: in the case where the code runs fine, with the objectWillChange.send() uncommented, a print statement in the EditTopicV init() shows that it runs twice. Why?
Any help would be greatly appreciated. I am using Xcode 13.2.1 and my deployment target is set to iOS 15.1.
Topic.swift:
struct Topic: Identifiable {
var name: String = "Default"
var iconName: String = "circle"
var id: String { name }
}
TopicListV.swift:
struct TopicListV: View {
#ObservedObject var tlVM: TopicListVM
#State var tappedTopic: Topic? = nil
#State var doEditTappedTopic = false
var body: some View {
VStack(alignment: .leading) {
List {
ForEach(tlVM.topics) { topic in
Button(action: {
tappedTopic = topic
// why is the following line needed?
tlVM.objectWillChange.send()
doEditTappedTopic = true
print("Tapped topic = \(tappedTopic!.name)")
}) {
Label(topic.name, systemImage: topic.iconName)
.padding(10)
}
}
}
Spacer()
}
.sheet(isPresented: $doEditTappedTopic) {
EditTopicV(tlVM: tlVM, originalTopic: self.tappedTopic!)
}
}
}
EditTopicV.swift (Editor View):
struct EditTopicV: View {
#ObservedObject var tlVM: TopicListVM
#Environment(\.presentationMode) var presentationMode
let originalTopic: Topic
#State private var editTopic: Topic
#State private var ic = "circle"
let iconList = ["circle", "leaf", "photo"]
init(tlVM: TopicListVM, originalTopic: Topic) {
print("DBG: EditTopicV: originalTopic = \(originalTopic)")
self.tlVM = tlVM
self.originalTopic = originalTopic
self._editTopic = .init(initialValue: originalTopic)
}
var body: some View {
VStack(alignment: .leading) {
HStack {
Button("Cancel") {
presentationMode.wrappedValue.dismiss()
}
Spacer()
Button("Save") {
editTopic.iconName = editTopic.iconName.lowercased()
tlVM.change(topic: originalTopic, to: editTopic)
presentationMode.wrappedValue.dismiss()
}
}
HStack {
Text("Name:")
TextField("name", text: $editTopic.name)
Spacer()
}
Picker("Color Theme", selection: $editTopic.iconName) {
ForEach(iconList, id: \.self) { icon in
Text(icon).tag(icon)
}
}
.pickerStyle(.segmented)
Spacer()
}
.padding()
}
}
TopicListVM.swift (Observable Object View Model):
class TopicListVM: ObservableObject {
#Published var topics = [Topic]()
func append(topic: Topic) {
topics.append(topic)
}
func change(topic: Topic, to newTopic: Topic) {
if let index = topics.firstIndex(where: { $0.name == topic.name }) {
topics[index] = newTopic
}
}
static func ex1() -> TopicListVM {
let tvm = TopicListVM()
tvm.append(topic: Topic(name: "leaves", iconName: "leaf"))
tvm.append(topic: Topic(name: "photos", iconName: "photo"))
tvm.append(topic: Topic(name: "shapes", iconName: "circle"))
return tvm
}
}
Here's what the list looks like:
Using sheet(isPresented:) has the tendency to cause issues like this because SwiftUI calculates the destination view in a sequence that doesn't always seem to make sense. In your case, using objectWillSend on the view model, even though it shouldn't have any effect, seems to delay the calculation of your force-unwrapped variable and avoids the crash.
To solve this, use the sheet(item:) form:
.sheet(item: $tappedTopic) { item in
EditTopicV(tlVM: tlVM, originalTopic: item)
}
Then, your item gets passed in the closure safely and there's no reason for a force unwrap.
You can also capture tappedTopic for a similar result, but you still have to force unwrap it, which is generally something we want to avoid:
.sheet(isPresented: $doEditTappedTopic) { [tappedTopic] in
EditTopicV(tlVM: tlVM, originalTopic: tappedTopic!)
}
Very strange behavior.
Click the back button on the subpage (Subview) to return to the main page (ContentView). However, the subpage (Subview) automatically opens again. Why?
import SwiftUI
struct ContentView: View {
#State var things: [String] = []
#State var count: Int = 0
var body: some View {
NavigationView{
List {
ForEach(things.indices, id: \.self) { index in
Text(things[index])
}
}
.onAppear {
update()
}
.navigationTitle("a")
.toolbar{
NavigationLink(destination: Subview(count: $count), label: {
Text("sub")
})
}
}
}
func update() {
things = []
for i in 0...count {
things.append(String(i))
}
}
}
struct Subview: View {
var count : Binding<Int>
var body: some View {
Text("sub")
.onAppear {
count.wrappedValue += 1
}
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
NavigationLink should always be inside a NavigationView. If you put it in the toolbar or some other place, you might run into weird issues.
Instead, use the init(destination:isActive:label:) initializer. Then set the presentingNextPage property to true when you want to present the next page.
struct ContentView: View {
#State var things: [String] = []
#State var count: Int = 0
#State var presentingNextPage = false
var body: some View {
NavigationView {
List {
ForEach(things.indices, id: \.self) { index in
Text(things[index])
}
/// placeholder navigation link
NavigationLink(destination: Subview(count: $count), isActive: $presentingNextPage) {
EmptyView()
}
}
.onAppear {
self.update()
}
.navigationTitle("a")
.toolbar{
ToolbarItem(placement: .navigationBarTrailing) {
Button("sub") {
presentingNextPage = true /// set to true
}
}
}
}
}
func update() {
things = []
for i in 0...count {
things.append(String(i))
}
}
}
Result:
Put "onAppear{...}" on the NavigationView not the List, like this:
struct ContentView: View {
#State var things: [String] = []
#State var count: Int = 0
var body: some View {
NavigationView{
List {
ForEach(things.indices, id: \.self) { index in
Text(things[index])
}
}
.navigationTitle("a")
.toolbar{
NavigationLink(destination: Subview(count: $count), label: {
Text("sub")
})
}
}
.onAppear { // <---
update()
}
}
I have a List with multiple Section and each Section has different type of data. For each section I want clicking on an item to present a popover.
Problem is that if I attach the .popover to the Section or ForEach then the .popover seems to be applied to every entry in the list. So the popover gets created for each item even when just one is clicked.
Example code is below. I cannot attach the .popover to the List because, in my case, there are 2 different styles of .popover and each view can only have a single .popover attached to it.
struct Item: Identifiable {
var id = UUID()
var title: String
}
var items: [Item] = [
Item(title: "Item 1"),
Item(title: "Item 2"),
Item(title: "Item 3"),
]
struct PopoverView: View {
#State var item: Item
var body: some View {
print("new PopoverView")
return Text("View for \(item.title)")
}
}
struct ContentView: View {
#State var currentItem: Item?
var body: some View {
List {
Section(header: Text("Items")) {
ForEach(items) { item in
Button(action: { currentItem = item }) {
Text("\(item.title)")
}
}
}
}
}
}
The current best solution I have come up with is to attach the popover to each Button and then only allow one popover based on currentItem,
Button(action: { currentItem = item }) {
Text("\(item.title)")
}
.popover(isPresented: .init(get: { currentItem == item },
set: { $0 ? (currentItem = item) : (currentItem = nil) })) {
PopoverView(item: item)
}
Any better way to do this?
Bonus points to solve this: When I used my hack, the drag down motion seems to glitch and the view appears from the top again. Not sure what the deal with that is.
You can always create a separate view for your item.
struct MyGreatItemView: View {
#State var isPresented = false
var item: Item
var body: some View {
Button(action: { isPresented = true }) {
Text("\(item.title)")
}
.popover(isPresented: $isPresented) {
PopoverView(item: item)
}
}
}
And implement it to ContentView:
struct ContentView: View {
var body: some View {
List {
Section(header: Text("Items")) {
ForEach(items) { item in
MyGreatItemView(item: item)
}
}
}
}
}
Trying to reach component like sheet or popover in ForEach causes problems.
I've also faced the glitch you mentioned, but below (with sheet) works as expected;
List {
Section(header: Text("Items")) {
ForEach(items) { item in
Button(action: { currentItem = item }) {
Text("\(item.title)")
}
}
}
}
.sheet(item: $currentItem, content: PopoverView.init)
Here's a late suggestion, I used a ViewModifier to hold the show Popover state on each view, the modifier also builds the Popover menu and also handles the presented sheet initiated from the popover menu. (Here's some code...)
struct Item: Identifiable {
var id = UUID()
var title: String
}
var items: [Item] = [
Item(title: "Item 1"),
Item(title: "Item 2"),
Item(title: "Item 3"),
]
struct ContentView: View {
var body: some View {
List {
Section(header: Text("Items")) {
ForEach(items) { item in
Text("\(item.title)").popoverWithSheet(item: item)
}
}
}
}
}
struct SheetFromPopover: View {
#State var item: Item
var body: some View {
print("new Sheet from Popover")
return Text("Sheet for \(item.title)")
}
}
struct PopoverModifierForView : ViewModifier {
#State var showSheet : Bool = false
#State var showPopover : Bool = false
var item : Item
var tap: some Gesture {
TapGesture(count: 1)
.onEnded { _ in self.showPopover = true }
}
func body(content: Content) -> some View {
content
.popover(isPresented: $showPopover,
attachmentAnchor: .point(.bottom),
arrowEdge: .bottom) {
self.createPopover()
}
.sheet(isPresented: self.$showSheet) {
SheetFromPopover(item: item)
}
.gesture(tap)
}
func createPopover() -> some View {
VStack {
Button(action: {
self.showPopover = false
self.showSheet = true
}) {
Text("Show Sheet...")
}.padding()
Button(action: {
print("Something Else..")
}) {
Text("Something Else")
}.padding()
}
}
}
extension View {
func popoverWithSheet(item: Item) -> some View {
modifier(PopoverModifierForView(item: item))
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
With following code:
struct HomeView: View {
var body: some View {
NavigationView {
List(dataTypes) { dataType in
NavigationLink(destination: AnotherView()) {
HomeViewRow(dataType: dataType)
}
}
}
}
}
What's weird, when HomeView appears, NavigationLink immediately loads the AnotherView. As a result, all AnotherView dependencies are loaded as well, even though it's not visible on the screen yet. The user has to click on the row to make it appear.
My AnotherView contains a DataSource, where various things happen. The issue is that whole DataSource is loaded at this point, including some timers etc.
Am I doing something wrong..? How to handle it in such way, that AnotherView gets loaded once the user presses on that HomeViewRow?
The best way I have found to combat this issue is by using a Lazy View.
struct NavigationLazyView<Content: View>: View {
let build: () -> Content
init(_ build: #autoclosure #escaping () -> Content) {
self.build = build
}
var body: Content {
build()
}
}
Then the NavigationLink would look like this. You would place the View you want to be displayed inside ()
NavigationLink(destination: NavigationLazyView(DetailView(data: DataModel))) { Text("Item") }
EDIT: See #MwcsMac's answer for a cleaner solution which wraps View creation inside a closure and only initializes it once the view is rendered.
It takes a custom ForEach to do what you are asking for since the function builder does have to evaluate the expression
NavigationLink(destination: AnotherView()) {
HomeViewRow(dataType: dataType)
}
for each visible row to be able to show HomeViewRow(dataType:), in which case AnotherView() must be initialized too.
So to avoid this a custom ForEach is necessary.
import SwiftUI
struct LoadLaterView: View {
var body: some View {
HomeView()
}
}
struct DataType: Identifiable {
let id = UUID()
var i: Int
}
struct ForEachLazyNavigationLink<Data: RandomAccessCollection, Content: View, Destination: View>: View where Data.Element: Identifiable {
var data: Data
var destination: (Data.Element) -> (Destination)
var content: (Data.Element) -> (Content)
#State var selected: Data.Element? = nil
#State var active: Bool = false
var body: some View {
VStack{
NavigationLink(destination: {
VStack{
if self.selected != nil {
self.destination(self.selected!)
} else {
EmptyView()
}
}
}(), isActive: $active){
Text("Hidden navigation link")
.background(Color.orange)
.hidden()
}
List{
ForEach(data) { (element: Data.Element) in
Button(action: {
self.selected = element
self.active = true
}) { self.content(element) }
}
}
}
}
}
struct HomeView: View {
#State var dataTypes: [DataType] = {
return (0...99).map{
return DataType(i: $0)
}
}()
var body: some View {
NavigationView{
ForEachLazyNavigationLink(data: dataTypes, destination: {
return AnotherView(i: $0.i)
}, content: {
return HomeViewRow(dataType: $0)
})
}
}
}
struct HomeViewRow: View {
var dataType: DataType
var body: some View {
Text("Home View \(dataType.i)")
}
}
struct AnotherView: View {
init(i: Int) {
print("Init AnotherView \(i.description)")
self.i = i
}
var i: Int
var body: some View {
print("Loading AnotherView \(i.description)")
return Text("hello \(i.description)").onAppear {
print("onAppear AnotherView \(self.i.description)")
}
}
}
I had the same issue where I might have had a list of 50 items, that then loaded 50 views for the detail view that called an API (which resulted in 50 additional images being downloaded).
The answer for me was to use .onAppear to trigger all logic that needs to be executed when the view appears on screen (like setting off your timers).
struct AnotherView: View {
var body: some View {
VStack{
Text("Hello World!")
}.onAppear {
print("I only printed when the view appeared")
// trigger whatever you need to here instead of on init
}
}
}
For iOS 14 SwiftUI.
Non-elegant solution for lazy navigation destination loading, using view modifier, based on this post.
extension View {
func navigate<Value, Destination: View>(
item: Binding<Value?>,
#ViewBuilder content: #escaping (Value) -> Destination
) -> some View {
return self.modifier(Navigator(item: item, content: content))
}
}
private struct Navigator<Value, Destination: View>: ViewModifier {
let item: Binding<Value?>
let content: (Value) -> Destination
public func body(content: Content) -> some View {
content
.background(
NavigationLink(
destination: { () -> AnyView in
if let value = self.item.wrappedValue {
return AnyView(self.content(value))
} else {
return AnyView(EmptyView())
}
}(),
isActive: Binding<Bool>(
get: { self.item.wrappedValue != nil },
set: { newValue in
if newValue == false {
self.item.wrappedValue = nil
}
}
),
label: EmptyView.init
)
)
}
}
Call it like this:
struct ExampleView: View {
#State
private var date: Date? = nil
var body: some View {
VStack {
Text("Source view")
Button("Send", action: {
self.date = Date()
})
}
.navigate(
item: self.$date,
content: {
VStack {
Text("Destination view")
Text($0.debugDescription)
}
}
)
}
}
I was recently struggling with this issue (for a navigation row component for forms), and this did the trick for me:
#State private var shouldShowDestination = false
NavigationLink(destination: DestinationView(), isActive: $shouldShowDestination) {
Button("More info") {
self.shouldShowDestination = true
}
}
Simply wrap a Button with the NavigationLink, which activation is to be controlled with the button.
Now, if you're to have multiple button+links within the same view, and not an activation State property for each, you should rely on this initializer
/// Creates an instance that presents `destination` when `selection` is set
/// to `tag`.
public init<V>(destination: Destination, tag: V, selection: Binding<V?>, #ViewBuilder label: () -> Label) where V : Hashable
https://developer.apple.com/documentation/swiftui/navigationlink/3364637-init
Along the lines of this example:
struct ContentView: View {
#State private var selection: String? = nil
var body: some View {
NavigationView {
VStack {
NavigationLink(destination: Text("Second View"), tag: "Second", selection: $selection) {
Button("Tap to show second") {
self.selection = "Second"
}
}
NavigationLink(destination: Text("Third View"), tag: "Third", selection: $selection) {
Button("Tap to show third") {
self.selection = "Third"
}
}
}
.navigationBarTitle("Navigation")
}
}
}
More info (and the slightly modified example above) taken from https://www.hackingwithswift.com/articles/216/complete-guide-to-navigationview-in-swiftui (under "Programmatic navigation").
Alternatively, create a custom view component (with embedded NavigationLink), such as this one
struct FormNavigationRow<Destination: View>: View {
let title: String
let destination: Destination
var body: some View {
NavigationLink(destination: destination, isActive: $shouldShowDestination) {
Button(title) {
self.shouldShowDestination = true
}
}
}
// MARK: Private
#State private var shouldShowDestination = false
}
and use it repeatedly as part of a Form (or List):
Form {
FormNavigationRow(title: "One", destination: Text("1"))
FormNavigationRow(title: "Two", destination: Text("2"))
FormNavigationRow(title: "Three", destination: Text("3"))
}
In the destination view you should listen to the event onAppear and put there all code that needs to be executed only when the new screen appears. Like this:
struct DestinationView: View {
var body: some View {
Text("Hello world!")
.onAppear {
// Do something important here, like fetching data from REST API
// This code will only be executed when the view appears
}
}
}