I love the SwiftUI previews, and I'm trying to see many variants of the view at the same time,
but failing to update the #State variables.
struct TestView: View {
#State fileprivate var text :String = "Hello, "
fileprivate var text2 :String = "World!"
var body: some View {
Text(text + text2)
}
func customize(_ fn: (Self)->(Self)) -> Self {
return fn(self)
}
}
struct TestView_Previews: PreviewProvider {
static var previews: some View {
TestView()
TestView()
.customize() { slf in
var next = slf
next.text = "こんにちは"
// next.text = State(wrappedValue: "こんにちは") // Compile error
next.text2 = "世界"
return next
}
.previewDisplayName("Testing")
}
}
This shows:
You can see that the text property is not changed. Why and how can I fix this?
Related
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()
}
}
Here I got an extension which works fine for updating itself at lunch, but after Lunch or Appear, it does not reports the change of data to its View.
My Goal: I want my Extension get sensitive to value that is reporting.
import SwiftUI
struct ContentView: View {
#State var changeString: String = "Hello, world!"
var body: some View {
customText().stringOfText(changeString).padding()
Button("change") { changeString = "Omid" }.padding()
Text(changeString).padding()
}
}
struct customText: View {
#State var stringOfText = ""
var body: some View
{
Text(stringOfText)
}
}
extension customText {
func stringOfText(_ text: String) -> customText {
customText(stringOfText: text)
}
}
It should not be state inside, because state is not recreated, ie. you need
struct customText: View {
var stringOfText: String = "" // << here !!
var body: some View {
Text(stringOfText)
}
}
I'm currently developing an application using SwiftUI.
I want to use a UserDefaults value in this app.
So I made a code below.
But in this case, when I reboot the app(the 4'th process in the process below), I can't get value from UserDefaults...
Build and Run this project.
Pless the home button and the app goes to the background.
Double-tap the home button and remove the app screen.
press the app icon and reboot the app. Then I want to get value from UserDefaults.
to resolve this problem how should I set and get a value in UserDefaults?
Here is the code:
import SwiftUI
struct ContentView: View {
#State var text = "initialText"
var body: some View {
VStack {
Text(text)
TextField( "", text: $text)
}.onAppear(){
if let text = UserDefaults.standard.object(forKey: "text" ){
self.text = text as! String
}
}
.onDisappear(){
UserDefaults.standard.set(self.text, forKey: "text")
}
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
ADD
When I add this class following the first answer, that code has a couple of errors like this, is it usual?
Xcode: Version 11.7
Swift: Swift 5
Set in a class like this your values: Bool, String(see example), Int, etc...
#if os(iOS)
import UIKit
#else
import AppKit
#endif
import Combine
#propertyWrapper struct UserDefault<T> {
let key: String
let defaultValue: T
init(_ key: String, defaultValue: T) {
self.key = key
self.defaultValue = defaultValue
}
var wrappedValue: T {
get {
return UserDefaults.standard.object(forKey: key) as? T ?? defaultValue
}
set {
UserDefaults.standard.set(newValue, forKey: key)
}
}
}
final class UserSettings: ObservableObject {
let objectWillChange = PassthroughSubject<Void, Never>()
#UserDefault("myText", defaultValue: "initialText")
var myText: String {
willSet { objectWillChange.send() }
}
}
this to read:
let settings = UserSettings()
let count = settings.countSentence // default countsentence 1
this to update:
let settings = UserSettings()
settings.countSentence = 3 // default countsentence 3
Based on your code:
struct ContentView: View {
let UserDef = UserSettings()
#State var text = ""
var body: some View {
VStack {
Text(UserDef.myText)
TextField("placeholder", text: $text, onCommit: { self.UserDef.myText = self.text})
}.onAppear() {
self.text = self.UserDef.myText
}
}
}
I have created a simple List and want to add users to it. My project has CoreDate activated and I have add the following Code to the SceneDelegate:
let userStorage = UserStorage()
let contentView = ContentView().environment(\.managedObjectContext, context).environmentObject(userStorage)
The code of the ContentView is this:
import SwiftUI
struct User: Identifiable {
var id = UUID()
var firstName = ""
var lastName = ""
}
class UserStorage: ObservableObject {
#Published var users = [User]()
}
struct ContentView: View {
#State private var presentation = false
#EnvironmentObject var userStorage: UserStorage
var body: some View {
VStack {
Button(action: {
self.presentation = true
}) {
Text("New User")
}.sheet(isPresented: $presentation, onDismiss: {
self.presentation = false
}) {
newuserView(presentation: self.$presentation, newUser: User())
}
List(userStorage.users) { singleUser in
VStack {
Text(singleUser.firstName)
Text(singleUser.lastName)
}
}
}
}
}
struct newuserView : View {
#Binding var presentation: Bool
#State var newUser: User
#EnvironmentObject var userStarage: UserStorage
var body: some View {
VStack {
TextField("Put in first name please", text:$newUser.firstName)
TextField("Put in last name please", text:$newUser.lastName)
Button(action: {
self.userStarage.users.append(self.newUser)
self.presentation = false
}) {
Text("Add new User")
}disabled(newUser.lastName.isEmpty || newUser.firstName.isEmpty)
}.padding(.horizontal)
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
When I run my project and want to add a user, I get the following error:
Thread 1: Fatal error: No ObservableObject of type UserStorage found.
A View.environmentObject(_:) for UserStorage may be missing as an ancestor of this view.
I have tried to do this with .sheet, but it doesn't work
Sheet creates different view hierarchy so .environmentObject is not injected in view to be shown in sheet by default - you have to do it manually
}.sheet(isPresented: $presentation, onDismiss: {
self.presentation = false
}) {
newuserView(presentation: self.$presentation, newUser: User())
.environmentObject(self.userStorage)
}
My code is a little more complex than this so I created an example that gets the same error.
When I navigate into a view, I have a function I want to perform with a variable passed into this view. That function then produces an array. I then want to put that array into a List, but I get an error.
How do I get the List to show the produced array?
I think the issue is the List can't be updated because it already has the declared blank array.
struct ContentView : View {
#State var array = [String]()
var body: some View {
List(self.array,id: \.self) { item in
Text("\(item)")
}
.onAppear(perform: createArrayItems)
}
func createArrayItems() {
array = ["item1", "item2", "item3", "item4", "item5"]
}
}
You can use ObservableObject data providers(eg : ViewModel) with #Published properties.
struct ListView: View {
#ObservedObject var viewModel = ListViewModel()
var body: some View {
NavigationView {
List(){
ForEach(viewModel.items) { item in
Text(item)
}
}
}
}
}
#if DEBUG
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ListView()
}
}
#endif
class ListViewModel: ObservableObject {
#Published var items = ["item1", "item2", "item3", "item4", "item5","item6"]
func addItem(){
items.append("item7")
}
}
You can use combine framework to update the list.
Whenever a change is made in DataProvider Object it will automatically update the list.
struct ContentView : View {
#EnvironmentObject var data: DataProvider
var body: some View {
NavigationView {
NavigationButton(destination: SecondPage()) {
Text("Go to Second Page")
}
List {
ForEach(data.array.identified(by: \.self)) { item in
Text("\(item)")
}
}
}
}
}
Add items in the list
struct SecondPage : View {
#State var counter = 1
#EnvironmentObject var tempArray: DataProvider
var body: some View {
VStack {
Button(action: {
self.tempArray.array.append("item\(self.counter)")
self.counter += 1
}) {
Text("Add items")
}
Text("Number of items added \(counter-1)")
}
}
}
It will simply notify the change
import Combine
final class DataProvider: BindableObject {
let didChange = PassthroughSubject<DataProvider, Never>()
var array = [String]() {
didSet {
didChange.send(self)
}
}
}
You also need to do some update in the SceneDelegate. This update ensures that ContentView has a DataProvider object in the environment.
window.rootViewController = UIHostingController(rootView: ContentView().environmentObject(DataProvider()))
#txagPman
I too have your problem to understand how to modify a list.
I was able to write this code.
I hope it's useful.
import SwiftUI
struct ContentView: View {
#State private var array = createArrayItems()
// #State private var array = [""] - This work
// #State private var array = [] - This not work
#State private var text = ""
var body: some View {
VStack {
TextField("Text", text: $text, onCommit: {
// self.array = createArrayItems() - This work after press return on textfield
self.array.append(self.text)
}).padding()
List (self.array, id: \.self) {item in
Text("\(item)")
}
}
// .onAppear {
// self.array = createArrayItems() - This not work
// }
}
}
func createArrayItems() -> [String] {
return ["item_01","item_02","item_03","item_04" ]
}
A dumb UI is a good UI
Keep your views dumb try the following code to create a dynamic List
import UIKit
import SwiftUI
import PlaygroundSupport
struct ContentView : View {
#State var array = [String]()
var body: some View {
List{
ForEach(array.identified(by: \.self)) { item in
Text("\(item)")
}
}
}
}
func createArrayItems()->[String] {
return ["item1", "item2", "item3", "item4", "item5","item6"]
}
PlaygroundPage.current.liveView = UIHostingController(rootView: ContentView(array: createArrayItems()))
Use this:
class ObservableArray<T>: ObservableObject {
#Published var array: [T]
init(array: [T] = ) {
self.array = array
}
init(repeating value: T, count: Int) {
array = Array(repeating: value, count: count)
}
}
struct YourView: View {
#ObservedObject var array = ObservableArray<String>()
var body: some View {
}
}