High-level description:
There is a nested view problem when a state object is being passed through views. At the end of the deepest view in the hierarchy, the app is frozen and memory consumption is increasing continuously.
Use-case
Partners list → Partner detail → (Locations list) → Location detail
Code-snippets
class PartnerViewModel: ObservableObject {
#Published var partners: [Partner] = Partner.partners
}
This view is loaded into a TabView and a NavigationStack components in the parent class.
struct PartnerListView: View {
#StateObject var viewModel = PartnerViewModel()
var body: some View {
List($viewModel.partners, id: \.self) { $partner in
NavigationLink {
PartnerDetailView(partner: $partner)
} label: {
Text(partner.name)
}
}
}
}
struct PartnerDetailView: View {
#Binding var partner: Partner
var body: some View {
Form {
Section("Locations") {
List($partner.locations, id: \.self) { $location in
NavigationLink {
LocationDetailView(location: $location)
} label: {
Text(location.name)
}
}
}
}
}
}
struct LocationDetailView: View {
#Binding var location: Location
var body: some View {
TextField("Name", text: $location.name)
}
}
The following snippets are workaround and it works but it might be temporary because I don't understand why the first attempt doesn't work and why this one does. I haven't found any resources that could give an example of this scenario.
struct PartnerDetailView: View {
#Binding var partner: Partner
var body: some View {
Form {
Section("Locations") {
List($partner.locations, id: \.self) { $location in
NavigationLink {
LocationDetailView(partner: $partner, locationIndex: partner.locations.firstIndex(of: location) ?? 0)
} label: {
Text(location.name)
}
}
}
}
}
}
struct LocationDetailView: View {
#Binding var partner: Partner
var locationIndex: Int
var body: some View {
TextField("Name", text: $partner.locations[locationIndex].name)
}
}
Is it possible that I am not passing values between views properly?🤔
Related
I am passing a Person binding from the first view to the second view to the third view, when I update the binding value in the third view it pops back to the second view, I understand that SwiftUI updates the views that depend on the state value, but is poping the current view is the expected behavior or I am doing something wrong?
struct Person: Identifiable {
let id = UUID()
var name: String
var numbers = [1, 2]
}
struct FirstView: View {
#State private var people = [Person(name: "Current Name")]
var body: some View {
NavigationView {
List($people) { $person in
NavigationLink(destination: SecondView(person: $person)) {
Text(person.name)
}
}
}
}
}
struct SecondView: View {
#Binding var person: Person
var body: some View {
Form {
NavigationLink(destination: ThirdView(person: $person)) {
Text("Update Info")
}
}
}
}
struct ThirdView: View {
#Binding var person: Person
var body: some View {
Form {
Button(action: {
person.numbers.append(3)
}) {
Text("Append a new number")
}
}
}
}
When navigating twice you need to either use isDetailLink(false) or StackNavigationViewStyle, e.g.
struct FirstView: View {
#State private var people = [Person(name: "Current Name")]
var body: some View {
NavigationView {
List($people) { $person in
NavigationLink(destination: SecondView(person: $person)) {
Text(person.name)
}
.isDetailLink(false) // option 1
}
}
.navigationViewStyle(.stack) // option 2
}
}
SwiftUI works by updating the rendered views to match what you have in your state.
In this case, you first have a list that contains an element called Current Name. Using a NavigationLink you select this item.
You update the name and now that previous element no longer exists, it's been replaced by a new element called New Name.
Since Current Name no longer exists, it also cannot be selected any longer, and the view pops back to the list.
To be able to edit the name without popping back, you'll need to make sure that the item on the list is the same, even if the name has changed. You can do this by using an Identifiable struct instead of a String.
struct Person: Identifiable {
let id = UUID().uuidString
var name = "Current Name"
}
struct ParentView: View {
#State private var people = [Person()]
var body: some View {
NavigationView {
List($people) { $person in
NavigationLink(destination: ChildView(person: $person)) {
Text(person.name)
}
}
}
}
}
struct ChildView: View {
#Binding var person: Person
var body: some View {
Button(action: {
person.name = "New Name"
}) {
Text("Update Name")
}
}
}
I am trying to create a binding to a FetchedResults item, error is on $items[i]:
struct NavView: View {
#Binding var item : Card
...
}
struct ContentView: View {
private var items: FetchedResults<Card>
var body: some View {
List {
ForEach(items.indices, id:\.self) { i in
NavigationLink {
NavView(item: $items[i])
}
}
}
}
}
Changing the Binding to ObservedObject compiles and seems to work properly, although I feel like I'm violating single source of truth policy by creating a new ObservedObject.
struct NavView: View {
#ObservedObject var item : Card
...
}
struct ContentView: View {
private var items: FetchedResults<Card>
var body: some View {
List {
ForEach(items) { item in
NavigationLink {
NavView(item: item)
}
}
}
}
}
I'd like to pass a range of an array in a model inside ForEach.
I recreated an example:
import SwiftUI
class TheModel: ObservableObject {
#Published var list: [Int] = [1,2,3,4,5,6,7,8,9,10]
}
struct MainView: View {
#StateObject var model = TheModel()
var body: some View {
VStack {
ForEach (0...1, id:\.self) { item in
SubView(subList: $model.list[0..<5]) <-- error if I put a range
}
}
}
}
struct SubView: View {
#Binding var subList: [Int]
var body: some View {
HStack {
ForEach (subList, id:\.self) { item in
Text("\(item)")
}
}
}
}
struct MainView_Previews: PreviewProvider {
static var previews: some View {
MainView()
}
}
The work around
I found is to pass all the list and perform the range inside the subView. But I'd like don't do this because the array is very big:
struct MainView: View {
#StateObject var model = TheModel()
var body: some View {
VStack {
ForEach (0...1, id:\.self) { i in
SubView(subList: $model.list, number: i, dimension: 5)
}
}
}
}
struct SubView: View {
#Binding var subList: [Int]
var number: Int
var dimension: Int
var body: some View {
HStack {
ForEach (subList[number*dimension..<dimension*(number+1)].indices, id:\.self) { idx in
Button(action: {
subList[idx] += 1
print(subList)
}, label: {
Text("num: \(subList[idx])")
})
}
}
}
}
I would pass the model to the subview since it is a class and will be passed by reference and then pass the range as a separate parameter.
Here is my new implementation of SubView
struct SubView: View {
var model: TheModel
var range: Range<Int>
var body: some View {
HStack {
ForEach (model.list[range].indices, id:\.self) { idx in
HStack {
Button(action: {
model.list[idx] += 1
print(model.list)
}, label: {
Text("num: \(model.list[idx])")
})
}
}
}
}
}
Note that I added indices to the ForEach header to make sure we access the array using an index and not with a value from the array.
The calling view would then look like
var body: some View {
VStack {
SubView(model: model, range: (0..<5))
Text("\(model.list.map(String.init).joined(separator: "-"))")
}
The extra Text is just there for testing purposes
When I use the "next article" button to jump to the article details page with index 3, I want to go directly back to the article list page instead of the article details page with index 2.I tried to search for methods to return to the specified page and destroy the page, but I didn't find them.How to achieve this effect in swiftui?Thanks.I guess the same scenario will happen in other mobile development, right?
The ArticleListView is :
struct ArticleListView: View {
#EnvironmentObject var modelData:ModelData
var body: some View {
NavigationView{
List{
ForEach(modelData.articleList){ article in
NavigationLink(destination:ArticleDetail(index:article.index)){
ArticleItem(index:article.index);
}
}
}
.listStyle(PlainListStyle())
}
}
}
The ArticleDetail is like this:
struct ArticleDetail: View {
#EnvironmentObject var modelData:ModelData
var index:Int
var body: some View {
VStack{
Text(modelData.articleList[index].htmlText)
NavigationLink(destination:ArticleDetail(index:self.index+1)){
Text("next article")
}
}
}
}
The Article/ArticleItemView/ModelData is like this:
struct Article:Identifiable{
var id = UUID()
var index:Int
var htmlText:String
}
struct ArticleItem: View {
#EnvironmentObject var modelData:ModelData
var index:Int
var body: some View {
Text(modelData.articleList[index].htmlText)
}
}
final class ModelData:ObservableObject {
#Published var articleList = [Article(index:0,htmlText: "first test text "),Article(index:1,htmlText: "second test text"),Article(index:2,htmlText: "third test text")]
}
This solution has some potential scalability issues, but it gets the basic job done:
struct Article {
var id = UUID()
}
struct ContentView: View {
var articles = [Article(), Article(), Article(), Article()]
#State private var activeId : UUID?
func activeBinding(id: UUID) -> Binding<Bool> {
.init { () -> Bool in
activeId == id
} set: { (newValue) in
activeId = newValue ? id : nil
}
}
var body: some View {
NavigationView {
VStack(alignment: .leading, spacing: 20) {
ForEach(articles, id: \.id) { article in
NavigationLink(destination: ArticleView(article: article,
articles: articles,
popToTop: { activeId = nil }),
isActive: activeBinding(id: article.id)) {
Text("Link to article: \(article.id)")
}
}
}
}
}
}
struct ArticleView : View {
var article : Article
var articles : [Article]
var popToTop: () -> Void
var body : some View {
VStack(alignment: .leading, spacing: 20) {
Text("Current: \(article.id)")
Button("Pop") {
popToTop()
}
ForEach(articles, id: \.id) { listArticle in
NavigationLink(destination: ArticleView(article: article, articles: articles, popToTop: popToTop)) {
Text("Link to article: \(listArticle.id)")
}
}
}
}
}
On the main page, the top-level article ID is stored in a #State variable. That is tied with a custom binding to an isActive property on the top-level link. Basically, when the article is active, the link is presented and when activeId is nil, the link becomes inactive, and pops to the top.
Because that's the top level view, any views lower in the stack will get popped off if that top-level NavigationLink is inactive.
popToTop is a function that gets passed down to the subsequent article views and gets called if the "Pop" button is pressed.
I have a view that contain users UsersContentView in this view there is a button which is extracted as a subview: RequestSearchButton(), and under the button there is a Text view which display the result if the user did request to search or no, and it is also extracted as a subview ResultSearchQuery().
struct UsersContentView: View {
var body: some View {
ZStack {
VStack {
RequestSearchButton()
ResultSearchQuery(didUserRequestSearchOrNo: .constant("YES"))
}
}
}
}
struct RequestSearchButton: View {
var body: some View {
Button(action: {
}) {
Text("User requested search")
}
}
}
struct ResultSearchQuery: View {
#Binding var didUserRequestSearchOrNo: String
var body: some View {
Text("Did user request search: \(didUserRequestSearchOrNo)")
}
}
How can I update the #Binding var didUserRequestSearchOrNo: String inside the ResultSearchQuery() When the button RequestSearchButton() is clicked. Its so confusing!
You need to track the State of a variable (which is indicating if a search is active or not) in your parent view, or your ViewModel if you want to extract the Variables. Then you can refer to this variable in enclosed child views like the Search Button or Search Query Results.
In this case a would prefer a Boolean value for the tracking because it's easy to handle and clear in meaning.
struct UsersContentView: View {
#State var requestedSearch = false
var body: some View {
ZStack {
VStack {
RequestSearchButton(requestedSearch: $requestedSearch)
ResultSearchQuery(requestedSearch: $requestedSearch)
}
}
}
}
struct RequestSearchButton: View {
#Binding var requestedSearch: Bool
var body: some View {
Button(action: {
requestedSearch.toggle()
}) {
Text("User requested search")
}
}
}
struct ResultSearchQuery: View {
#Binding var requestedSearch: Bool
var body: some View {
Text("Did user request search: \(requestedSearch.description)")
}
}
Actually I couldn't understand why you used two struct which are connected to eachother, you can do it in one struct and Control with a state var
struct ContentView: View {
var body: some View {
VStack {
RequestSearchButton()
}
}
}
struct RequestSearchButton: View {
#State private var clicked : Bool = false
var body: some View {
Button(action: {
clicked = true
}) {
Text("User requested search")
}
Text("Did user request search: \(clicked == true ? "YES" : "NO")")
}
}
if this is not what you are looking for, could you make a detailed explain.