I'm trying to use the new SwiftUI OutlineGroup to display an expandable tree. I tried this in my app's ContentView:
struct ContentView: View {
#EnvironmentObject var store: MyDataStore
var body: some View {
List {
OutlineGroup(store.navRoot, children: \.children) { item in
Text(item.name)
}
}
}
The code for the store and the command handler that tries to change the tree data:
// Clicking menu button calls this
private func newProject() {
var new = LeftNavNode(id: UUID(), name: "Foo")
store.navRoot.children!.append(new)
}
...
class MyDataStore: ObservableObject {
#Published var navRoot = LeftNavNode(id: projectsID, name: "Projects",
children: [
LeftNavNode(id: UUID(), name: "Project1"),
LeftNavNode(id: UUID(), name: "Project2")
])
}
struct LeftNavNode: Identifiable {
let id: UUID
let name: String
var children: [LeftNavNode]? = nil
}
It works to display static data, but when I add an item to the tree, I get an error. The state changes, the view re-renders, and I get this:
2020-09-20 15:08:24.991604-0400 MyArchives[32728:584579] [General] NSOutlineView error inserting child indexes <_NSCachedIndexSet: 0x600000760ea0>[number of indexes: 1 (in 1 ranges), indexes: (3)] in parent 0x0 (which has 1 children).
How do you change the tree model without crashing?
Related
I have a NavigationSplitView in my app, I have an #State variable in my detail view that gets created in init.
When I select something from the sidebar and the detail view renders, at first everything looks ok. But when I select a different item on the sidebar, the contents of the #state variable don't get recreated.
Using the debugger I can see the init of the detail view get called every time I select a new item in the sidebar, and I can see the #State variable get created. But when it actually renders, the #State variable still contains the previous selection's values.
I've reduced this problem to a test case I'll paste below. The top text in the detail view is a variable passed in from the sidebar, and the second line of text is generated by the #State variable. Expected behavior would be, if I select "one" the detail view would display "one" and "The name is one". If I select "two" the detail view would display "two" and "The name is two".
Instead, if I select "one" first, it displays correctly. But when I select "two", it displays "two" and "The name is one".
Note that if I select "two" as the first thing I do after launching the app, it correctly displays "two" and "The name is two", but when I click on "one" next, it will display "one" and "the name is two". So the state variable is being set once, then never changing again,
Here's the sample code and screenshots:
import SwiftUI
struct Item: Hashable, Identifiable {
let id = UUID()
let name: String
}
struct ContentView: View {
#State private var selectedItem: Item.ID? = nil
private let items = [Item(name: "one"), Item(name: "two"), Item(name: "three")]
func itemForID(_ id: UUID?) -> Item? {
guard let itemID = id else { return nil }
return items.first(where: { item in
item.id == itemID
})
}
var body: some View {
NavigationSplitView{
List(selection: $selectedItem) {
ForEach(items) { item in
Text(item.name)
.tag(item.id)
}
}
} detail: {
if let name = itemForID(selectedItem)?.name {
DetailView(name: name)
} else {
Text("Select an item")
}
}
}
}
struct DetailView: View {
#State var detailItem: DetailItem
var name: String
init(name: String) {
self.name = name
_detailItem = State(wrappedValue: DetailItem(name: name))
}
var body: some View {
VStack {
Text(name)
Text(detailItem.computedText)
}
}
}
struct DetailItem {
let name: String
var computedText: String {
return "The name is \(name)"
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
Question. What is the purpose of having detailItem as a #State? if you remove the #State, this test case works.
Will the way computedText change over time?
struct DetailView: View {
// #State var detailItem: DetailItem
var detailItem: DetailItem
var name: String
init(name: String) {
self.name = name
// _detailItem = State(wrappedValue: DetailItem(name: name))
detailItem = DetailItem(name: name)
}
var body: some View {
VStack {
Text(name)
Text(detailItem.computedText)
}
}
}
This has nothing to do with NavigationSplitView, but how you initialise #State property.
According to the Apple document on #State (https://developer.apple.com/documentation/swiftui/state):
Don’t initialise a state property of a view at the point in the view hierarchy where you instantiate the view, because this can conflict with the storage management that SwiftUI provides.
As well as the documentation of init(wrappedValue:) (https://developer.apple.com/documentation/swiftui/state/wrappedvalue):
Don’t call this initializer directly. Instead, declare a property with the State attribute, and provide an initial value:
#State private var isPlaying: Bool = false
From my understanding, if you force to initialise the state in the view init, it will persist through the lifetime of the view, and subsequence change of it won't take any effect on the view.
The recommended way in Apple documentation is to create the struct in the parent view and pass it to the child view, and if you need to change the struct in the child view, use #Binding to allow read and write access.
If you want to ignore the documentation and force it to work, you can give an id to your DetailView, forcing it to refresh the view when the item id has changed:
var body: some View {
NavigationSplitView{
List(selection: $selectedItem) {
ForEach(items) { item in
Text(item.name)
.tag(item.id)
}
}
} detail: {
if let name = itemForID(selectedItem)?.name {
DetailView(name: name).id(selectedItem)
} else {
Text("Select an item")
}
}
}
Your Item struct is bad, if the name is unique it should be:
struct Item: Identifiable {
var id: String { name }
let name: String
}
Otherwise:
struct Item: Identifiable {
let id = UUID()
let name: String
}
When I update a binding property from an array in a pushed view 2+ layers down, the navigation pops back instantly after a change to the property.
Xcode 13.3 beta, iOS 15.
I created a simple demo and code is below.
Shopping Lists
List Edit
List section Edit
Updating the list title (one view deep) is fine, navigation stack stays same, and changes are published if I return. But when adjusting a section title (two deep) the navigation pops back as soon as I make a single change to the property.
I have a feeling I'm missing basic fundamentals here, and I have a feeling it must be related to the lists id? but I'm struggling to figure it out or work around it.
GIF
Code:
Models:
struct ShoppingList {
let id: String = UUID().uuidString
var title: String
var sections: [ShoppingListSection]
}
struct ShoppingListSection {
let id: String = UUID().uuidString
var title: String
}
View Model:
final class ShoppingListsViewModel: ObservableObject {
#Published var shoppingLists: [ShoppingList] = [
.init(
title: "Shopping List 01",
sections: [
.init(title: "Fresh food")
]
)
]
}
Content View:
struct ContentView: View {
var body: some View {
NavigationView {
ShoppingListsView()
}
}
}
ShoppingListsView
struct ShoppingListsView: View {
#StateObject private var viewModel = ShoppingListsViewModel()
var body: some View {
List($viewModel.shoppingLists, id: \.id) { $shoppingList in
NavigationLink(destination: ShoppingListEditView(shoppingList: $shoppingList)) {
Text(shoppingList.title)
}
}
.navigationBarTitle("Shopping Lists")
}
}
ShoppingListEditView
struct ShoppingListEditView: View {
#Binding var shoppingList: ShoppingList
var body: some View {
Form {
Section(header: Text("Title")) {
TextField("Title", text: $shoppingList.title)
}
Section(header: Text("Sections")) {
List($shoppingList.sections, id: \.id) { $section in
NavigationLink(destination: ShoppingListSectionEditView(section: $section)) {
Text(section.title)
}
}
}
}
.navigationBarTitle("Edit list")
}
}
ShoppingListSectionEditView
struct ShoppingListSectionEditView: View {
#Binding var section: ShoppingListSection
var body: some View {
Form {
Section(header: Text("Title")) {
TextField("title", text: $section.title)
}
}
.navigationBarTitle("Edit section")
}
}
try this, works for me:
struct ContentView: View {
var body: some View {
NavigationView {
ShoppingListsView()
}.navigationViewStyle(.stack) // <--- here
}
}
Try to make you object confirm to Identifiable and return value which unique and stable, for your case is ShoppingList.
Detail view seems will pop when object id changed.
The reason your stack is popping back to the root ShoppingListsView is that the change in the list is published and the root ShoppingListsView is registered to listen for updates to the #StateObject.
Therefore, any change to the list is listened to by ShoppingListsView, causing that view to be re-rendered and for all new views on the stack to be popped in order to render the root ShoppingListsView, which is listening for updates on the #StateObject.
The solution to this is to change the #StateObject to #EnvironmentObject
Please refactor your code to change ShoppingListsViewModel to use an #EnvironmentObject wrapper instead of a #StateObject wrapper
You may pass the environment object in to all your child views and also add a boolean #Published flag to track any updates to the data.
Then your ShoppingListView would look as below
struct ShoppingListsView: View {
#EnvironmentObject var viewModel = ShoppingListsViewModel()
var body: some View {
List($viewModel.shoppingLists, id: \.id) { $shoppingList in
NavigationLink(destination: ShoppingListEditView(shoppingList: $shoppingList)) {
Text(shoppingList.title)
}
}
.navigationBarTitle("Shopping Lists")
}
}
Don't forget to pass the viewModel in to all your child views.
That should fix your problem.
When I delete an element of an array using onDelete(), it removes the correct item in the data but removes the last item on the UI. I saw this answer but I am already using what it recommends. Any advice?
struct ContentView: View {
#State var items = ["One", "Two", "Three"]
var body: some View {
Form{
ForEach(items.indices, id:\.self){ itemIndex in
let item = self.items[itemIndex]
EditorView(container: self.$items, index: itemIndex, text: item)
}.onDelete(perform: { indexSet in
self.items.remove(atOffsets: indexSet)
})
}
}
}
Here is the EditorView struct:
struct EditorView : View {
var container: Binding<[String]>
var index: Int
#State var text: String
var body: some View {
TextField("Type response here", text: self.$text, onCommit: {
self.container.wrappedValue[self.index] = self.text
})
}
}
Your ForEach is looping over the indices of your array, so that is what SwiftUI is using to identify them. When you delete an item, you have one fewer index for the array, so SwiftUI interprets that as the last one has been deleted.
To do this correctly, you should be looping over a list of Identifiable items that have a unique id. Here I've created a struct called MyItem which holds the original String and a uniquely generated id. I use .map(MyItem.init) to convert the items into a [MyItem].
Also, your code needs the index in the loop, so loop over Array(items.enumerated()) which will give you an array of (offset, element) tuples. Then tell SwiftUI to use \.element.id as the id.
Note that EditorView now takes an Array of MyItem.
With these changes, SwiftUI will be able to identify the item you have deleted from the list and update the UI correctly.
struct MyItem: Identifiable {
var name: String
let id = UUID()
}
struct ContentView: View {
#State var items = ["One", "Two", "Three"].map(MyItem.init)
var body: some View {
Form{
ForEach(Array(items.enumerated()), id: \.element.id) { index, item in
EditorView(container: self.$items, index: index, text: item.name)
}.onDelete(perform: { indexSet in
self.items.remove(atOffsets: indexSet)
})
}
}
}
struct EditorView : View {
var container: Binding<[MyItem]>
var index: Int
#State var text: String
var body: some View {
TextField("Type response here", text: self.$text, onCommit: {
self.container.wrappedValue[self.index].name = self.text
})
}
}
I have a model which, for the sake of example, is a tag cloud and a model for items:
struct TagCloud: Identifiable, Hashable{
var id: Int
let tag: String
static func tagCloud() -> [TagCloud]{
return [ TagCloud(id: 01, tag:"Green"),
TagCloud(id: 02, tag:"Blue"),
TagCloud(id: 03, tag:"Red")]
}
}
struct TaggedItem: Identifiable, Hashable{
var id: Int
let tag: String
let item: String
static func taggedItems() -> [TaggedItem]{
return [ TaggedItem(id: 01, tag:"Green", item: "Tree"),
TaggedItem(id: 02, tag:"Blue", item: "Sky"),
TaggedItem(id: 03, tag:"Red", item: "Apple")...]
}
}
I have a class to 'contain' the currently selected items:
class SelectedItems: ObservableObject {
#Published var currentlySelectedItems:[TaggedItem] = []
func changeData(forTag tag: String ){
let currentSelection = TaggedItem. taggedItems()
let filteredList = cardCollection.filter { $0.tag == tag }
currentlySelectedItems = filteredList
}
}
In my parent view, I select one of the tags from the cloud:
struct ParentView: View {
let tagCloud = TagCloud.tagCloud()
#ObservedObject var currentSelection : TaggedItem = TaggedItem()
#State var navigationTag:Int? = nil
var body: some View {
NavigationLink(destination: ChildView(), tag: 1, selection: $tag) {
EmptyView()
}
VStack{
ScrollView(.horizontal, content: {
HStack(spacing: 20){
ForEach( self.tagCloud, id: \.self) { item in
VStack{
Button(action: {
self. currentSelection.changeData(forTag: item.tag )
self.navigationTag = 1
}){
Text(item.tag)
}.buttonStyle(PlainButtonStyle())
..
}
The child view contains the ObservedObject. As a side note, I have also set this as an EnvironmentObject.
struct ChildView: View {
#ObservedObject var currentItems : SelectedItems = SelectedItems()
var body: some View {
VStack{
ScrollView(.horizontal, content: {
HStack(spacing: 20){
ForEach( currentItems.currentlySelectedItems, id: \.self) { item in
...
The problem:
In the parent view, the button calls SelectedItems in order to create a filtered list of items that match the selected tag
The call is made and the list is set (verified by print)
However, the data never "reaches" the child view
I tried a number of things with init(). I tried passing the selected tag to the child, and then doing the filtering within init() itself, but was stymied by the need to bind to a class. I read elsewhere to try having a second model which would be updated by the FIRST model in order to trigger a view refresh.
What is the correct way to create this filtered list via a parent view selection and make the list available in the child view?
This part should be rethink:
let tagCloud = TagCloud.tagCloud()
#ObservedObject var currentSelection : TaggedItem = TaggedItem()
^^ is a struct, it cannot be observed !!!
#ObservedObject must be applied only to #ObservableObject as you did for SelectedItems, so probably another ObservableObject view model wrapper around TaggedItem is expected here.
I'm starting with SwiftUI and I'm running into a roadblock with array items of an ObservableObject not saving to the main object.
Main object:
class Batch: Codable, Identifiable, ObservableObject {
let id: String
var items = [Item]()
}
Item object:
class Item: Codable, Identifiable, ObservableObject {
let id: String
var description: String
}
I have a BatchView which I pass a batch into:
struct BatchView: View {
#ObservedObject var batch: Batch
var body: some View {
List {
ForEach(batch.items) { item in
ItemView(item: item)
}
}
.navigationBarTitle(batch.items.reduce("", { $0 + $1.description }))
}
}
In the ItemView I change the description:
struct ItemView: View {
#ObservedObject var item: Item
#State private var descr = ""
var body: some View {
VStack(alignment: .leading) {
Text("MANUFACTURED")
TextField("", text: $descr) {
self.updateDescr(descr: self.descr)
}
}
}
private func updateDescr(descr: String) {
item.description = descr
}
}
But when I update the description for a batch item, the title of BatchView doesn't change, so the changes to the Item isn't coming back to the root Batch.
How do I make the above work?
This answer helped me. I had to explicitly add #Published in front of the variable I was changing.