I have a conditional view based on 2 binding vars in MyBootomSheet.
Idea is, show detail view if an item is selected in parent view, else show list of items.
ParentView has the logic to select/unselect item.
The code works as expected for the first time. But once an item is selected in the parent view the view never gets updated ever again, even after another item selected or item is unselected.
Any idea how this can be resolved ?
TIA!
struct ParentView: View {
#StateObject var dataSource = MapViewSource()
#State var selectedItem:SomeModel? = nil
var body: some View {
//
}.bottomSheet() {
MyBottomSheet(items:self.$dataSource.items, selectedItem:self.$selectedItem)
}
}
struct MyBottomSheet: View {
#Binding var items:[SomeModel]
#Binding var selectedItem:SomeModel?
var body: some View {
if self.selectedItem != nil {
ItemDetail(item: self.selectedItem!)
}
else {
List(self.items id: \.itemId) { item in
ItemRow(item: item)
}
}
}
}
State uses Binding for childviews but StateObject needs an ObservedObject:
class SomeObservableObject: ObservableObject {
// if this wasn't published, then the view wouldn't update when only changing the value
#Published var value: String
init(_ value: String) {
self.value = value
}
}
struct ParentView: View {
#State var state: String = "This is a State"
#StateObject var stateObject: SomeObservableObject = .init("This is an ObservableObject")
var body: some View {
ChildView(state: $state, stateObject: stateObject)
}
}
struct ChildView: View {
#Binding var state: String
#ObservedObject var stateObject: SomeObservableObject
var body: some View {
VStack {
Text("State: \(state)")
Text("StateObject: \(stateObject.value)")
}
}
}
``
Related
I have a simple view that shows some photos, through a list. Clicking on any row should display a detailed view of that photo. I'm using the MVVM pattern. However, an infinite loop occurs when I try to set the “selectedPhoto” property of the view model. Is there any way to avoid this loop without having to create a property in the detailed view itself?
Here is the Photo struct:
struct Photo: Identifiable {
var id = UUID()
var name: String
}
Here is the ContentView with an extension (the “updatePhoto” method is causing the infinite loop):
struct ContentView: View {
#StateObject private var viewModel = ViewModel()
var body: some View {
NavigationView {
List {
ForEach(viewModel.photos) { selectedPhoto in
showDetailView(with: selectedPhoto)
}
}
.navigationTitle("Favorite Photo")
}
}
}
extension ContentView {
func showDetailView(with selectedPhoto: Photo?) -> some View {
if let selectedPhoto = selectedPhoto {
viewModel.updatePhoto(selectedPhoto)
}
return DetailView(viewModel: viewModel)
}
}
Here is the view model:
class ViewModel: ObservableObject {
#Published var photos = [
Photo(name: "Photo 1"),
Photo(name: "Photo 2"),
Photo(name: "Photo 3")
]
#Published var selectedPhoto: Photo?
func updatePhoto(_ selectedPhoto: Photo?) {
self.selectedPhoto = selectedPhoto
}
}
And here is the DetailView:
struct DetailView: View {
#ObservedObject private var viewModel: ViewModel
init(viewModel: ViewModel) {
self.viewModel = viewModel
}
var body: some View {
Text(viewModel.selectedPhoto?.name ?? "Unknown photo name")
}
}
Try this approach, using a NavigationLink to present the DetailView,
and passing the selectedPhoto to it using #State var selectedPhoto: Photo.
struct Photo: Identifiable {
let id = UUID()
var name: String
}
class ViewModel: ObservableObject {
#Published var photos = [Photo(name: "Photo 1"),Photo(name: "Photo 2"),Photo(name: "Photo 3")]
}
struct DetailView: View {
#State var selectedPhoto: Photo
var body: some View {
Text(selectedPhoto.name)
}
}
struct ContentView: View {
#StateObject var viewModel = ViewModel()
var body: some View {
NavigationView {
List {
ForEach(viewModel.photos) { selectedPhoto in
NavigationLink(selectedPhoto.name, destination: DetailView(selectedPhoto: selectedPhoto))
}
}
.navigationTitle("Favorite Photo")
}
}
}
Note that NavigationView is being deprecated and you will have to use NavigationStack instead.
Let's say we have a parent view like:
struct ParentView: View {
#State var text: String = ""
var body: some View {
ChildView(text: $text)
}
}
Child view like:
struct ChildView: View {
#ObservedObject var childViewModel: ChildViewModel
init(text: Binding<String>) {
self.childViewModel = ChildViewModel(text: text)
}
var body: some View {
...
}
}
And a view model for the child view:
class ChildViewModel: ObservableObject {
#Published var value = false
#Binding var text: String
init(text: Binding<String>) {
self._text = text
}
...
}
Making changes on the String binding inside the child's view model makes the ChildView re-draw causing the viewModel to recreate itself and hence reset the #Published parameter to its default value. What is the best way to handle this in your opinion?
Cheers!
The best way is to use a custom struct as a single source of truth, and pass a binding into child views, e.g.
struct ChildViewConfig {
var value = false
var text: String = ""
// mutating funcs for logic
mutating func reset() {
text = ""
}
}
struct ParentView: View {
#State var config = ChildViewConfig()
var body: some View {
ChildView(config: $config)
}
}
struct ChildView: View {
#Binding var config: ChildViewConfig
var body: some View {
TextField("Text", text: $config.text)
...
Button("Reset") {
config.reset()
}
}
}
"ViewConfig can maintain invariants on its properties and be tested independently. And because ViewConfig is a value type, any change to a property of ViewConfig, like its text, is visible as a change to ViewConfig itself." [Data Essentials in SwiftUI WWDC 2020].
I want to have a mother view that displays a different child view based on a #State bool.
However I get two errors when doing that.
On the start of the body closure:
Struct 'ViewBuilder' requires that 'EmptyCommands' conform to 'View'
Return type of property 'body' requires that 'EmptyCommands' conform
to 'View'
And inside the control flow statement:
Closure containing control flow statement cannot be used with result
builder 'CommandsBuilder'
struct ResultView: View {
#State var resultViewSuccess = false
let resultViewModel: ResultViewModel
var body: some View {
Group {
if let showresultView = resultViewSuccess {
ViewOne(viewModel: resultViewModel)
} else {
ViewTwo(
resultViewSuccess: $resultViewSuccess,
viewModel: resultViewModel,
)
}
}
}
}
struct ViewTwo: View {
#Binding var resultViewSuccess: Bool
#StateObject var viewModel: ResultViewModel
var body: some View {
NavigationView {
ButtonResult(
resultViewSuccess: $resultViewSuccess,
viewModel: viewModel)
}
}
struct ButtonResult: View {
#Binding var resultViewSuccess: Bool
#StateObject var viewModel: ResultViewModel
var body: some View {
Button(action: {
self.resultViewSuccess = true
}) {
Text("View Results")
}
}
}
I refer to two questions that I already asked and have been answered very well by Asperi: SwiftUI ForEach with .indices() does not update after onDelete,
SwiftUI onDelete List with Toggle
Now I tried to modify the closure in ForEach with a NavigationLink and suddenly the App crashes again with
Thread 1: Fatal error: Index out of range
when I try to swipe-delete.
Code:
class Model: ObservableObject {
#Published var name: String
#Published var items: [Item]
init(name: String, items: [Item]) {
self.name = name
self.items = items
}
}
struct Item: Identifiable {
var id = UUID()
var isOn: Bool
}
struct ContentView: View {
#EnvironmentObject var model: Model
var body: some View {
NavigationView {
List {
ForEach(model.items) {item in
NavigationLink(destination: DetailView(item: self.makeBinding(id: item.id))) {
Toggle(isOn: self.makeBinding(id: item.id).isOn)
{Text("Toggle-Text")}
}
}.onDelete(perform: delete)
}
}
}
func delete(at offsets: IndexSet) {
self.model.items.remove(atOffsets: offsets)
}
func makeBinding(id: UUID) -> Binding<Item> {
guard let index = self.model.items.firstIndex(where: {$0.id == id}) else {
fatalError("This person does not exist")
}
return Binding(get: {self.model.items[index]}, set: {self.model.items[index] = $0})
}
}
struct DetailView: View {
#Binding var item: Item
var body: some View {
Toggle(isOn: $item.isOn) {
Text("Toggle-Text")
}
}
}
It works without NavigationLink OR without the Toggle. So it seems for me that I only can use the makeBinding-Function once in this closure.
Thanks for help
Your code was crashing for me with and even without Navigation Link. Sometimes only if I deleted the last object in the Array. It looks like it was still trying to access an index out of the array. The difference to your example you linked above, is that they didn't used EnvironmentObject to access the array. The stored the array directly in the #State.
I came up with a little different approach, by declaring Item as ObservedObject and then simply pass it to the subview where you can use their values as Binding, without any function.
I changed Item to..
class Item: ObservableObject {
var id = UUID()
var isOn: Bool
init(id: UUID, isOn: Bool)
{
self.id = id
self.isOn = isOn
}
}
Change the ContentView to this..
struct ContentView: View {
#EnvironmentObject var model: Model
var body: some View {
NavigationView {
List {
ForEach(model.items, id:\.id) {item in
NavigationLink(destination: DetailView(item: item)) {
Toggler(item: item)
}
}.onDelete(perform: delete)
}
}
}
I outsourced the Toggle to a different view, where we pass the ObservedObject to, same for the DetailView.
struct Toggler: View {
#ObservedObject var item : Item
var body : some View
{
Toggle(isOn: $item.isOn)
{Text("Toggle-Text")}
}
}
struct DetailView: View {
#ObservedObject var item: Item
var body: some View {
Toggle(isOn: $item.isOn) {
Text("Toggle-Text")
}
}
}
They both take an Item as ObservedObject and use it as Binding for the Toggle.
I use a modal sheet whose content is updated for each call. However, when the content is marked as #State, the view body is never updated.
Is anyone seeing this as well? Is a workaround available?
This is the calling view:
struct ContentView: View {
#State var isPresented = false
#State var i = 0
var body: some View {
List {
Button("0") {
self.i = 0
self.isPresented = true
}
Button("1") {
self.i = 1
self.isPresented = true
}
}
.sheet(
isPresented: $isPresented,
content: {
SheetViewNOK(i: self.i)
}
)
}
}
This does work:
struct SheetViewOK: View {
var i: Int
var body: some View {
Text("Hello \(i)") // String is always updated
}
}
This does not work. But obviously, in a real app, I need to use #State because changes made by the user need to be reflected in the sheet's content:
struct SheetViewNOK: View {
#State var i: Int
var body: some View {
Text("Hello \(i)") // String is never updated after creation
}
}
In your .sheet you are passing the value of your ContentView #State to a new #State. So it will be independent from the ContentView.
To create a connection or a binding of your ContentView #State value, you should define your SheetView var as #Binding. With this edit you will pass the binding of your state value to your sheet view.
struct SheetView: View {
#Binding var i: Int
var body: some View {
Text("Hello \(i)")
}
}
struct ContentView: View {
#State var isPresented = false
#State var i: Int = 0
var body: some View {
List {
Button("0") {
self.i = 0
self.isPresented = true
}
Button("1") {
self.i = 1
self.isPresented = true
}
}.sheet(
isPresented: $isPresented,
content: {
SheetView(i: self.$i)
})
}
}
There are 3 different ways
use a binding
use multiple .sheets
use $item
This is fully explained in this video.
Multiple Sheets in a SwiftUI View