Here is my test code:
struct ArrView: View {
#State var arr: [String] = ["first", "second"]
var body: some View {
VStack {
Button("append") {self.arr.append("item\(self.arr.count)")}
List(arr.indices) {row in
Text(self.arr[row])
}
}
}
}
When the 'append' Button was pressed, the List view didn't update.
Am I doing wrong?
You can use ForEach<Range>() only if the provided data is a constant, otherwise you need to use ForEach(_:id:content:) and provide an id explicitly, like this:
struct ArrView: View {
#State var arr: [String] = ["first", "second"]
var body: some View {
VStack {
Button("append") {self.arr.append("item\(self.arr.count)")}
List(arr, id: \.self) { item in
Text(item)
}
}
}
}
I don't think it is the proper way to create List view. Here is a sample
struct ContentView: View {
#State var arr: [String] = ["first", "second"]
var body: some View {
VStack {
Button("append") {self.arr.append("item\(self.arr.count)")}
List(self.arr, id: \.self) { str in
Text(str)
}
}
}
}
Related
Sorry if my question is silly, I am a beginner to programming. I have a Navigation Link to a detail view from a List produced from my view model's array. In the detail view, I want to be able to mutate one of the tapped-on element's properties, but I can't seem to figure out how to do this. I don't think I explained that very well, so here is the code.
// model
struct Activity: Identifiable {
var id = UUID()
var name: String
var completeDescription: String
var completions: Int = 0
}
// view model
class ActivityViewModel: ObservableObject {
#Published var activities: [Activity] = []
}
// view
struct ActivityView: View {
#StateObject var viewModel = ActivityViewModel()
#State private var showingAddEditActivityView = false
var body: some View {
NavigationView {
VStack {
List {
ForEach(viewModel.activities, id: \.id) {
activity in
NavigationLink(destination: ActivityDetailView(activity: activity, viewModel: self.viewModel)) {
HStack {
VStack {
Text(activity.name)
Text(activity.miniDescription)
}
Text("\(activity.completions)")
}
}
}
}
}
.navigationBarItems(trailing: Button("Add new"){
self.showingAddEditActivityView.toggle()
})
.navigationTitle(Text("Activity List"))
}
.sheet(isPresented: $showingAddEditActivityView) {
AddEditActivityView(copyViewModel: self.viewModel)
}
}
}
// detail view
struct ActivityDetailView: View {
#State var activity: Activity
#ObservedObject var viewModel: ActivityViewModel
var body: some View {
VStack {
Text("Number of times completed: \(activity.completions)")
Button("Increment completion count"){
activity.completions += 1
updateCompletionCount()
}
Text("\(activity.completeDescription)")
}
}
func updateCompletionCount() {
var tempActivity = viewModel.activities.first{ activity in activity.id == self.activity.id
}!
tempActivity.completions += 1
}
}
// Add new activity view (doesn't have anything to do with question)
struct AddEditActivityView: View {
#ObservedObject var copyViewModel : ActivityViewModel
#State private var activityName: String = ""
#State private var description: String = ""
var body: some View {
VStack {
TextField("Enter an activity", text: $activityName)
TextField("Enter an activity description", text: $description)
Button("Save"){
// I want this to be outside of my view
saveActivity()
}
}
}
func saveActivity() {
copyViewModel.activities.append(Activity(name: self.activityName, completeDescription: self.description))
print(copyViewModel.activities)
}
}
In the detail view, I am trying to update the completion count of that specific activity, and have it update my view model. The method I tried above probably doesn't make sense and obviously doesn't work. I've just left it to show what I tried.
Thanks for any assistance or insight.
The problem is here:
struct ActivityDetailView: View {
#State var activity: Activity
...
This needs to be a #Binding in order for changes to be reflected back in the parent view. There's also no need to pass in the entire viewModel in - once you have the #Binding, you can get rid of it.
// detail view
struct ActivityDetailView: View {
#Binding var activity: Activity /// here!
var body: some View {
VStack {
Text("Number of times completed: \(activity.completions)")
Button("Increment completion count"){
activity.completions += 1
}
Text("\(activity.completeDescription)")
}
}
}
But how do you get the Binding? If you're using iOS 15, you can directly loop over $viewModel.activities:
/// here!
ForEach($viewModel.activities, id: \.id) { $activity in
NavigationLink(destination: ActivityDetailView(activity: $activity)) {
HStack {
VStack {
Text(activity.name)
Text(activity.miniDescription)
}
Text("\(activity.completions)")
}
}
}
And for iOS 14 or below, you'll need to loop over indices instead. But it works.
/// from https://stackoverflow.com/a/66944424/14351818
ForEach(Array(zip(viewModel.activities.indices, viewModel.activities)), id: \.1.id) { (index, activity) in
NavigationLink(destination: ActivityDetailView(activity: $viewModel.activities[index])) {
HStack {
VStack {
Text(activity.name)
Text(activity.miniDescription)
}
Text("\(activity.completions)")
}
}
}
You are changing and increment the value of tempActivity so it will not affect the main array or data source.
You can add one update function inside the view model and call from view.
The view model is responsible for this updation.
class ActivityViewModel: ObservableObject {
#Published var activities: [Activity] = []
func updateCompletionCount(for id: UUID) {
if let index = activities.firstIndex(where: {$0.id == id}) {
self.activities[index].completions += 1
}
}
}
struct ActivityDetailView: View {
var activity: Activity
var viewModel: ActivityViewModel
var body: some View {
VStack {
Text("Number of times completed: \(activity.completions)")
Button("Increment completion count"){
updateCompletionCount()
}
Text("\(activity.completeDescription)")
}
}
func updateCompletionCount() {
self.viewModel.updateCompletionCount(for: activity.id)
}
}
Not needed #State or #ObservedObject for details view if don't have further action.
I'm trying to use NavigationLink's isActive variable to pop back to the root view controller.
The problem I'm experiencing is that using isActive pushes the wrong row when clicking on a list item. Remove the isActive variable and everything works as expected.
Here's some example code for demonstration purposes:
struct ContentView: View {
#State private var activateNavigationLink: Bool = false
var exampleData = ["a", "b", "c"]
var body: some View {
NavigationView {
List(exampleData, id: \.self) { item in
NavigationLink(
destination: SecondView(item: item), isActive: $activateNavigationLink) {
Text(item)
}
}
}
}
}
SecondView
struct SecondView: View {
var item: String
var body: some View {
Text(item)
}
}
This is driving me nuts. Any help would be greatly appreciated.
Because activateNavigationLink is just a Bool in your code, if it is true, every NavigationLink will register as active in your List. Right now, this is manifesting as the last item (C) getting pushed each time.
Instead, you'd need some system to store which item is active and then translate that to a boolean binding for the NavigationLink to use.
Here's one possible solution:
struct ContentView: View {
#State private var activeNavigationLink: String? = nil
var exampleData = ["a", "b", "c"]
func bindingForItem(item: String) -> Binding<Bool> {
.init {
activeNavigationLink == item
} set: { newValue in
activeNavigationLink = newValue ? item : nil
}
}
var body: some View {
NavigationView {
List(exampleData, id: \.self) { item in
NavigationLink(
destination: SecondView(item: item), isActive: bindingForItem(item: item)) {
Text(item)
}
}
}
}
}
You should not use activeNavigationLink on main view it should be used with cellView
struct ContentView: View {
var exampleData = ["a", "b", "c"]
var body: some View {
NavigationView {
List(exampleData, id: \.self) { item in
CellView(item: item)
}
}
}
}
CellView
struct CellView: View {
#State private var activateNavigationLink: Bool = false
var item: String
var body: some View {
NavigationLink(
destination: SecondView(item: item), isActive: $activateNavigationLink) {
Text(item)
}
}
}
SecondView
struct SecondView: View {
var item: String
var body: some View {
Text(item)
}
}
This is the test data model:
class Item: Identifiable {
let name: String
init( n: Int) {
self.name = "\(n)"
}
}
class Storage: ObservableObject {
#Published var items = [Item( n: 1), Item( n: 2)]
func reverse() {
items = self.items.reversed()
}
}
This is my content view, with a NavigationLink and a detail view with a button that reverses the item order:
struct ContentView: View {
#ObservedObject
var storage = Storage()
var body: some View {
NavigationView {
List {
ForEach( storage.items) { item in
NavigationLink( destination: Button( action: {
self.storage.reverse()
}) {
Text("Reverse")
}) {
Text( item.name).padding()
}
}
}
}
}
}
Now if I tap on Reverse the NavigationView or List seems to lose its selection, pops the view, and pushes it again:
Is this expected behaviour or a bug in SwiftUI? Is there a workaround? I would expect that the detail view simply stays as it is, without reloading.
You need to specify an explicit id for your ForEach loop.
If you use a static ForEach (without the id parameter) your view is rebuilt because the data (storage.items) is changed.
Try the following:
struct ContentView: View {
#ObservedObject
var storage = Storage()
var body: some View {
NavigationView {
List {
ForEach(storage.items, id:\.name) { item in // <- add `id` parameter
NavigationLink(destination: self.destinationView) {
Text(item.name).padding()
}
}
}
}
}
var destinationView: some View {
Button(action: {
self.storage.reverse()
}) {
Text("Reverse")
}
}
}
This method, however, only works if the original position of selected item is maintained.
In this example performing the update() from the detail screen for item 1 will not pop the NavigationLink.
class Storage: ObservableObject {
#Published var items = [Item(n: 1), Item(n: 2)]
func update() {
items = [Item(n: 1), Item(n: 3)]
}
}
Here is a workaround to make it work (use an empty NavigationLink):
struct ContentView: View {
#ObservedObject var storage = Storage()
#State var isLinkActive = false
var body: some View {
NavigationView {
VStack {
List {
ForEach(storage.items, id:\.name) { item in
Button(action: {
self.isLinkActive = true
}) {
Text(item.name).padding()
}
}
}
NavigationLink(destination: self.destinationView, isActive: $isLinkActive) {
EmptyView()
}
}
}
}
var destinationView: some View {
Button(action: {
self.storage.reverse()
}) {
Text("Reverse")
}
}
}
I am trying to create a list using ForEach and NavigationLink of an array of data.
I believe my code (see the end of the post) is correct but my build fails due to
"Missing argument for parameter 'index' in call" and takes me to SceneDelegate.swift a place I haven't had to venture before.
// Create the SwiftUI view that provides the window contents.
let contentView = ContentView()
I can get the code to run if I amend to;
let contentView = ContentView(habits: HabitsList(), index: 1)
but then all my links hold the same data, which makes sense since I am naming the index position.
I have tried, index: self.index (which is what I am using in my NavigationLink) and get a different error message - Cannot convert value of type '(Any) -> Int' to expected argument type 'Int'
Below are snippets of my code for reference;
struct HabitItem: Identifiable, Codable {
let id = UUID()
let name: String
let description: String
let amount: Int
}
class HabitsList: ObservableObject {
#Published var items = [HabitItem]()
}
struct ContentView: View {
#ObservedObject var habits = HabitsList()
#State private var showingAddHabit = false
var index: Int
var body: some View {
NavigationView {
List {
ForEach(habits.items) { item in
NavigationLink(destination: HabitDetail(habits: self.habits, index: self.index)) {
HStack {
VStack(alignment: .leading) {
Text(item.name)
.font(.headline)
Text(item.description)
}
}
}
}
}
}
}
}
struct HabitDetail: View {
#Environment(\.presentationMode) var presentationMode
#ObservedObject var habits: HabitsList
var index: Int
var body: some View {
NavigationView {
Form {
Text(self.habits.items[index].name)
}
}
}
}
You probably don't need to pass the whole ObservedObject to the HabitDetail.
Passing just a HabitItem should be enough:
struct HabitDetail: View {
#Environment(\.presentationMode) var presentationMode
let item: HabitItem
var body: some View {
// remove `NavigationView` form the detail view
Form {
Text(item.name)
}
}
}
Then you can modify your ContentView:
struct ContentView: View {
#ObservedObject var habits = HabitsList()
#State private var showingAddHabit = false
var body: some View {
NavigationView {
List {
// for every item in habits create a `linkView`
ForEach(habits.items, id:\.id) { item in
self.linkView(item: item)
}
}
}
}
// extract to another function for clarity
func linkView(item: HabitItem) -> some View {
// pass just a `HabitItem` to the `HabitDetail`
NavigationLink(destination: HabitDetail(item: item)) {
HStack {
VStack(alignment: .leading) {
Text(item.name)
.font(.headline)
Text(item.description)
}
}
}
}
}
I'm trying to create a Favorite list where I can add different items but it doesn't work. I made a simple code to show you what's going on.
// BookData gets data from Json
struct BookData: Codable {
var titolo: String
var descrizione: String
}
class FavoriteItems: ObservableObject {
#Published var favItems: [String] = []
}
struct ContentView: View {
#ObservedObject var bookData = BookDataLoader()
#ObservedObject var favoriteItems = FavoriteItems()
var body: some View {
NavigationView {
List {
NavigationLink(destination: FavoriteView()) {
Text("Go to favorites")
}
ForEach(0 ..< bookData.booksData.count) { num in
HStack {
Text("\(self.bookData.booksData[num].titolo)")
Button(action: {
self.favoriteItems.favItems.append(self.bookData.booksData[num].titolo)
}) {
Image(systemName: "heart")
}
}
}
}
}
}
}
struct FavoriteView: View {
#ObservedObject var favoriteItems = FavoriteItems()
var body: some View {
List {
ForEach (0 ..< favoriteItems.favItems.count) { num in
Text("\(self.favoriteItems.favItems[num])")
}
}
}
}
When I launch the app I can go to the Favorite View but after adding an Item I cannot.
My aim is to add an Item to Favorites and be able to save it once I close the app
The view model favoriteItems inside ContentView needs to be passed into FavoriteView because you need a reference of favoriteItems to reload FavoriteView when you add a new data.
Change to
NavigationView(destination: FavoriteView(favoriteItems: favoriteItems)) #ObservedObject var favoriteItems: FavoriteItems
It will be fine.
Thanks, X_X