I have an array of views stored in a variable that I want to render. This seems pretty straightforward and simple to me -- however, SwiftUI fails to render it. Does anyone know why this is so?
struct TestView: View {
#State private var currentSelectedView = 0
#State private var quote = "Hello 123"
var body: some View { // Failed to produce diagnostic for expression
let viewArray = [FirstTextView(quote:$quote), SecondTextView(quote:$quote)]
viewArray[0]
viewArray[1]
}
}
struct FirstTextView: View {
#Binding var quote:String
var body: some View {
Text(quote)
}
}
struct SecondTextView: View {
#Binding var quote:String
var body: some View {
Text(quote)
}
}
struct TestView_Previews: PreviewProvider {
static var previews: some View {
TestView()
}
}
Try this. The problem was the elements of array were different types.
var body: some View {
let viewArray = [AnyView(FirstTextView(quote:$quote)), AnyView(SecondTextView(quote:$quote))]
viewArray[0]
viewArray[1]
}
I started studying SwiftUI and wanted to make a prototype of standard reminders, like in an iPhone. It seems nothing complicated, there is a List, in each cell a TextField.
But I ran into a problem: when we change the text in the TextField using onChange, then we accordingly tell the view model to update our objects.
And when the objects are updated, the entire List is redrawn and the editing of the current TextField is reset (you can neither remove more than one character, nor add). You have to click on the text again to continue editing.
Does anyone know how to treat this?
This is my code:
import SwiftUI
struct Fruit: Identifiable {
let id = UUID()
let name: String
func updateName(newName: String) -> Fruit {
return Fruit(name: newName)
}
}
class ViewModel: ObservableObject {
#Published var fruits: [Fruit] = [Fruit(name: "apple"), Fruit(name: "banana"), Fruit(name: "orange")]
func updateName(newName: String, fruit: Fruit) {
if let index = fruits.firstIndex(where: { $0.id == fruit.id }) {
fruits[index] = fruit.updateName(newName: newName)
}
}
}
struct ListView: View {
#StateObject var viewModel = ViewModel()
var body: some View {
List {
ForEach(viewModel.fruits) { fruit in
ListViewRow(fruit: fruit)
}
}
.environmentObject(viewModel)
}
}
struct ListViewRow: View {
#EnvironmentObject var viewModel: ViewModel
#State var fruitTextField: String
let fruit: Fruit
init(fruit: Fruit) {
self.fruit = fruit
_fruitTextField = State(initialValue: fruit.name)
}
var body: some View {
TextField("", text: $fruitTextField)
.onChange(of: fruitTextField) { newValue in
viewModel.updateName(newName: newValue, fruit: fruit)
}
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ListView()
}
}
You can simplify it even more with:
struct Fruit: Identifiable {
let id = UUID()
var name: String
}
class ViewModel: ObservableObject {
#Published var fruits: [Fruit] = [Fruit(name: "apple"), Fruit(name: "banana"), Fruit(name: "orange")]
}
struct ListView: View {
#StateObject var viewModel = ViewModel()
var body: some View {
List {
ForEach($viewModel.fruits) { $fruit in
ListViewRow(fruit: $fruit)
}
}
}
}
struct ListViewRow: View {
#Binding var fruit: Fruit
var body: some View {
TextField("", text: $fruit.name)
}
}
That being said, you really need to view the Apple Swift Tutorials that were linked in the comments.
Edit: Full Project Code for Lorem Ipsum:
//
// ContentView.swift
// FruitApp
//
// Created by Developer on 11/27/21.
//
import SwiftUI
struct Fruit: Identifiable {
let id = UUID()
var name: String
}
class ViewModel: ObservableObject {
#Published var fruits: [Fruit] = [Fruit(name: "apple"), Fruit(name: "banana"), Fruit(name: "orange")]
}
struct ListView: View {
#StateObject var viewModel = ViewModel()
var body: some View {
List {
ForEach($viewModel.fruits) { $fruit in
ListViewRow(fruit: $fruit)
}
}
}
}
struct ListViewRow: View {
#Binding var fruit: Fruit
var body: some View {
TextField("", text: $fruit.name)
}
}
struct ContentView: View {
var body: some View {
ListView()
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
Swiftui: I can show the data from db in list ,but it shown nothing in picker, how can I fix it
here is my ContentView:
import SwiftUI
struct ContentView: View {
#ObservedObject var model = PostListViewModel()
#State private var selectedStrength = 0
var body: some View {
// List(model.posts) { post in
// Text(post.name)
// }
Picker(selection: $selectedStrength, label: Text("picker")) {
ForEach(model.posts) { post in
Text(post.name)
}
}
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
try this or something similar:
ForEach(model.posts, id: \.self) { post in
Text(post.name)
}
I wanted to create quiet a simple app on watchOS 6, but after Apple has changed the ObjectBindig in Xcode 11 beta 5 my App does not run anymore. I simply want to synchronize data between two Views.
So I have rewritten my App with the new #Published, but I can't really set it up:
class UserInput: ObservableObject {
#Published var score: Int = 0
}
struct ContentView: View {
#ObservedObject var input = UserInput()
var body: some View {
VStack {
Text("Hello World\(self.input.score)")
Button(action: {self.input.score += 1})
{
Text("Adder")
}
NavigationLink(destination: secondScreen()) {
Text("Next View")
}
}
}
}
struct secondScreen: View {
#ObservedObject var input = UserInput()
var body: some View {
VStack {
Text("Button has been pushed \(input.score)")
Button(action: {self.input.score += 1
}) {
Text("Adder")
}
}
}
}
Your code has a couple of errors:
1) You didn't put your ContentView in a NavigationView, so the navigation between the two views never happened.
2) You used data binding in a wrong way. If you need the second view to rely on some state belonging to the first view you need to pass a binding to that state to the second view. Both in your first view and in your second view you had an #ObservedObject created inline:
#ObservedObject var input = UserInput()
so, the first view and the second one worked with two totally different objects. Instead, you are interested in sharing the score between the views. Let the first view own the UserInput object and just pass a binding to the score integer to the second view. This way both the views will work on the same value (you can copy paste the code below and try yourself).
import SwiftUI
class UserInput: ObservableObject {
#Published var score: Int = 0
}
struct ContentView: View {
#ObservedObject var input = UserInput()
var body: some View {
NavigationView {
VStack {
Text("Hello World\(self.input.score)")
Button(action: {self.input.score += 1})
{
Text("Adder")
}
NavigationLink(destination: secondScreen(score: self.$input.score)) {
Text("Next View")
}
}
}
}
}
struct secondScreen: View {
#Binding var score: Int
var body: some View {
VStack {
Text("Button has been pushed \(score)")
Button(action: {self.score += 1
}) {
Text("Adder")
}
}
}
}
#if DEBUG
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
#endif
If you really need it you can even pass the entire UserInput object to the second view:
import SwiftUI
class UserInput: ObservableObject {
#Published var score: Int = 0
}
struct ContentView: View {
#ObservedObject var input = UserInput() //please, note the difference between this...
var body: some View {
NavigationView {
VStack {
Text("Hello World\(self.input.score)")
Button(action: {self.input.score += 1})
{
Text("Adder")
}
NavigationLink(destination: secondScreen(input: self.input)) {
Text("Next View")
}
}
}
}
}
struct secondScreen: View {
#ObservedObject var input: UserInput //... and this!
var body: some View {
VStack {
Text("Button has been pushed \(input.score)")
Button(action: {self.input.score += 1
}) {
Text("Adder")
}
}
}
}
#if DEBUG
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
#endif
I tried a lot of different approaches on how to pass data from one view to another and came up with a solution that fits for simple and complex views / view models.
Version
Apple Swift version 5.3.1 (swiftlang-1200.0.41 clang-1200.0.32.8)
This solution works with iOS 14.0 upwards, because you need the .onChange() view modifier. The example is written in Swift Playgrounds. If you need an onChange like modifier for lower versions, you should write your own modifier.
Main View
The main view has a #StateObject viewModel handling all of the views logic, like the button tap and the "data" (testingID: String) -> Check the ViewModel
struct TestMainView: View {
#StateObject var viewModel: ViewModel = .init()
var body: some View {
VStack {
Button(action: { self.viewModel.didTapButton() }) {
Text("TAP")
}
Spacer()
SubView(text: $viewModel.testingID)
}.frame(width: 300, height: 400)
}
}
Main View Model (ViewModel)
The viewModel publishes a testID: String?. This testID can be any kind of object (e.g. configuration object a.s.o, you name it), for this example it is just a string also needed in the sub view.
final class ViewModel: ObservableObject {
#Published var testingID: String?
func didTapButton() {
self.testingID = UUID().uuidString
}
}
So by tapping the button, our ViewModel will update the testID. We also want this testID in our SubView and if it changes, we also want our SubView to recognize and handle these changes. Through the ViewModel #Published var testingID we are able to publish changes to our view. Now let's take a look at our SubView and SubViewModel.
SubView
So the SubView has its own #StateObject to handle its own logic. It is completely separated from other views and ViewModels. In this example the SubView only presents the testID from its MainView. But remember, it can be any kind of object like presets and configurations for a database request.
struct SubView: View {
#StateObject var viewModel: SubviewModel = .init()
#Binding var test: String?
init(text: Binding<String?>) {
self._test = text
}
var body: some View {
Text(self.viewModel.subViewText ?? "no text")
.onChange(of: self.test) { (text) in
self.viewModel.updateText(text: text)
}
.onAppear(perform: { self.viewModel.updateText(text: test) })
}
}
To "connect" our testingID published by our MainViewModel we initialize our SubView with a #Binding. So now we have the same testingID in our SubView. But we don't want to use it in the view directly, instead we need to pass the data into our SubViewModel, remember our SubViewModel is a #StateObject to handle all the logic. And we can't pass the value into our #StateObject during view initialization. Also if the data (testingID: String) changes in our MainViewModel, our SubViewModel should recognize and handle these changes.
Therefore we are using two ViewModifiers.
onChange
.onChange(of: self.test) { (text) in
self.viewModel.updateText(text: text)
}
The onChange modifier subscribes to changes in our #Binding property. So if it changes, these changes get passed to our SubViewModel. Note that your property needs to be Equatable. If you pass a more complex object, like a Struct, make sure to implement this protocol in your Struct.
onAppear
We need onAppear to handle the "first initial data" because onChange doesn't fire the first time your view gets initialized. It is only for changes.
.onAppear(perform: { self.viewModel.updateText(text: test) })
Ok and here is the SubViewModel, nothing more to explain to this one I guess.
class SubviewModel: ObservableObject {
#Published var subViewText: String?
func updateText(text: String?) {
self.subViewText = text
}
}
Now your data is in sync between your MainViewModel and SubViewModel and this approach works for large views with many subviews and subviews of these subviews and so on. It also keeps your views and corresponding viewModels enclosed with high reusability.
Working Example
Playground on GitHub:
https://github.com/luca251117/PassingDataBetweenViewModels
Additional Notes
Why I use onAppear and onChange instead of only onReceive: It appears that replacing these two modifiers with onReceive leads to a continuous data stream firing the SubViewModel updateText multiple times. If you need to stream data for presentation, it could be fine but if you want to handle network calls for example, this can lead to problems. That's why I prefer the "two modifier approach".
Personal Note: Please don't modify the StateObject outside the corresponding view's scope. Even if it is somehow possible, it is not what its meant for.
My question is still related to how to pass data between two views but I have a more complicated JSON data set and I am running into problems both with the passing the data and with it's initialization. I have something that works but I am sure it is not correct. Here is the code. Help!!!!
/ File: simpleContentView.swift
import SwiftUI
// Following is the more complicated #ObservedObject (Buddy and class Buddies)
struct Buddy : Codable, Identifiable, Hashable {
var id = UUID()
var TheirNames: TheirNames
var dob: String = ""
var school: String = ""
enum CodingKeys1: String, CodingKey {
case id = "id"
case Names = "Names"
case dob = "dob"
case school = "school"
}
}
struct TheirNames : Codable, Identifiable, Hashable {
var id = UUID()
var first: String = ""
var middle: String = ""
var last: String = ""
enum CodingKeys2: String, CodingKey {
case id = "id"
case first = "first"
case last = "last"
}
}
class Buddies: ObservableObject {
#Published var items: [Buddy] {
didSet {
let encoder = JSONEncoder()
if let encoded = try? encoder.encode(items) {UserDefaults.standard.set(encoded, forKey: "Items")}
}
}
#Published var buddy: Buddy
init() {
if let items = UserDefaults.standard.data(forKey: "Items") {
let decoder = JSONDecoder()
if let decoded = try? decoder.decode([Buddy].self, from: items) {
self.items = decoded
// ??? How to initialize here
self.buddy = Buddy(TheirNames: TheirNames(first: "c", middle: "r", last: "c"), dob: "1/1/1900", school: "hard nocks")
return
}
}
// ??? How to initialize here
self.buddy = Buddy(TheirNames: TheirNames(first: "c", middle: "r", last: "c"), dob: "1/1/1900", school: "hard nocks")
self.items = []
}
}
struct simpleContentView: View {
#Environment(\.presentationMode) var presentationMode
#State private var showingSheet = true
#ObservedObject var buddies = Buddies()
var body: some View {
VStack {
Text("Simple View")
Button(action: {self.showingSheet.toggle()}) {Image(systemName: "triangle")
}.sheet(isPresented: $showingSheet) {
simpleDetailView(buddies: self.buddies, item: self.buddies.buddy)}
}
}
}
struct simpleContentView_Previews: PreviewProvider {
static var previews: some View {
simpleContentView()
}
}
// End of File: simpleContentView.swift
// This is in a separate file: simpleDetailView.swift
import SwiftUI
struct simpleDetailView: View {
#Environment(\.presentationMode) var presentationMode
#ObservedObject var buddies = Buddies()
var item: Buddy
var body: some View {
VStack {
Text(/*#START_MENU_TOKEN#*/"Hello, World!"/*#END_MENU_TOKEN#*/)
Text("First Name = \(item.TheirNames.first)")
Button(action: {self.presentationMode.wrappedValue.dismiss()}){ Text("return"); Image(systemName: "gobackward")}
}
}
}
// ??? Correct way to make preview call
struct simpleDetailView_Previews: PreviewProvider {
static var previews: some View {
// ??? Correct way to call here
simpleDetailView(item: Buddy(TheirNames: TheirNames(first: "", middle: "", last: ""), dob: "", school: "") )
}
}
// end of: simpleDetailView.swift
Using directly #State variable will help you to achieve this, but if you want to sync that variable for both the screens using view model or #Published, this is what you can do. As the #State won't be binded to the #Published property. To achieve this follow these steps.
Step1: - Create a delegate to bind the value on pop or disappearing.
protocol BindingDelegate {
func updateOnPop(value : Int)
}
Step 2:- Follow the code base for Content View
class UserInput: ObservableObject {
#Published var score: Int = 0
}
struct ContentView: View , BindingDelegate {
#ObservedObject var input = UserInput()
#State var navIndex : Int? = nil
var body: some View {
NavigationView {
VStack {
Text("Hello World\(self.input.score)")
Button(action: {self.input.score += 1}) {
Text("Adder")
}
ZStack {
NavigationLink(destination: secondScreen(score: self.$input.score,
del: self, navIndex: $navIndex),
tag: 1, selection: $navIndex) {
EmptyView()
}
Button(action: {
self.navIndex = 1
}) {
Text("Next View")
}
}
}
}
}
func updateOnPop(value: Int) {
self.input.score = value
}
}
Step 3: Follow these steps for secondScreen
final class ViewModel : ObservableObject {
#Published var score : Int
init(_ value : Int) {
self.score = value
}
}
struct secondScreen: View {
#Binding var score: Int
#Binding var navIndex : Int?
#ObservedObject private var vm : ViewModel
var delegate : BindingDelegate?
init(score : Binding<Int>, del : BindingDelegate, navIndex : Binding<Int?>) {
self._score = score
self._navIndex = navIndex
self.delegate = del
self.vm = ViewModel(score.wrappedValue)
}
private var btnBack : some View { Button(action: {
self.delegate?.updateOnPop(value: self.vm.score)
self.navIndex = nil
}) {
HStack {
Text("Back")
}
}
}
var body: some View {
VStack {
Text("Button has been pushed \(vm.score)")
Button(action: {
self.vm.score += 1
}) {
Text("Adder")
}
}
.navigationBarBackButtonHidden(true)
.navigationBarItems(leading: btnBack)
}
}
Workaround at bottom of Question
I thought SwiftUI was supposed to automatically update views when data they were dependent on changed. However that isn't happening in the code below:
First I make a simple BindableObject
import SwiftUI
import Combine
class Example: BindableObject {
var didChange = PassthroughSubject<Void, Never>()
var test = 1 {
didSet {
didChange.send(())
}
}
}
Then the root view of the app:
struct BindTest : View {
#Binding var test: Example
var body: some View {
PresentationButton(destination: BindChange(test: $test)) {
ForEach(0..<test.test) { index in
Text("Invalidate Me! \(index)")
}
}
}
}
And finally the view in which I change the value of the BindableObject:
struct BindChange : View {
#Binding var test: Example
#Environment(\.isPresented) var isPresented
var body: some View {
Button(action: act) {
Text("Return")
}
}
func act() {
test.test = 2
isPresented?.value = false
}
}
When the return button is tapped there should be 2 instances of the Text View - but there is only 1. What am I doing wrong?
Also worth noting: If I change the #Binding to #EnvironmentObject the program just crashes when you tap the button producing this error:
Thread 1: EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0)
Full code below:
import SwiftUI
import Combine
class Example: BindableObject {
var didChange = PassthroughSubject<Example, Never>()
var test = 1 {
didSet {
didChange.send(self)
}
}
static let `default` = {
return Example()
}()
}
//Root View
struct BindTest : View {
#EnvironmentObject var test: Example
var body: some View {
PresentationButton(destination: BindChange()) {
ForEach(0..<test.test) { t in
Text("Invalidate Me! \(t)")
}
}
}
}
//View that changes the value of #Binding / #EnvironmentObject
struct BindChange : View {
#EnvironmentObject var test: Example
#Environment(\.isPresented) var isPresented
var body: some View {
Button(action: act) {
Text("Return")
}
}
func act() {
test.test = 2
isPresented?.value = false
}
}
#if DEBUG
struct ContentView_Previews : PreviewProvider {
static var previews: some View {
//ContentView().environmentObject(EntryStore())
BindTest().environmentObject(Example())
}
}
#endif
EDIT 2: Post's getting a little messy at this point but the crash with EnvironmentObject seems to be related to an issue with PresentationButton
By putting a NavigationButton inside a NavigationView the following code produces the correct result - invalidating the List when test.test changes:
//Root View
struct BindTest : View {
#EnvironmentObject var test: Example
var body: some View {
NavigationView {
NavigationButton(destination: BindChange()) {
ForEach(0..<test.test) { t in
Text("Functional Button #\(t)")
}
}
}
}
}