I'm beggining with SwiftUI and I wanted to develop a small simple app to practice. I have a problem with #Published property that don't pass through views and so don't update the view.
I explain : In the first view I calculate the vMoyenne property and update it. I wanted to show this value in the next view ("Passage") to be able to use it for some other calculation but I tried many thing and the value in the "Passage" View doesn't update...
Here is the code :
ContentView.swift :
struct ContentView: View {
var body: some View {
TabView {
SpeedView().tabItem {
Label("Vitesse", systemImage: "figure.run.circle.fill")
}
PassageView(parameters: Parameters()).tabItem {
Label("Passage", systemImage: "timer.circle.fill")
}
}
}
}
Parameters.swift
class Parameters: ObservableObject {
#Published var distance: Double?
static let units = ["m", "km"]
#Published var unit = 1
#Published var hour: Int = 0
#Published var minute: Int = 0
#Published var second: Int = 0
#Published var vMoyenne = 0.0
#Published var allure = 0.0
#Published var convertedDecimalToSeconds = 0
var time: Int?
...
func calcVMoy() -> Void{
var d = distance!
let t = Double(time!) / 3600
var unite: String {
return Parameters.units[unit]
}
var calc = 0.0
if unite == "km" {
calc = d / t
} else {
d = d / 1000
calc = d / t
}
vMoyenne = calc
}
...
init() {
}
}
**SpeedView.swift **
struct SpeedView: View {
#ObservedObject var parameters = Parameters()
...
...
Button {
showVMoy = true
disableChange = true
if parameters.distance == nil {
parameters.distance = 0
} else {
parameters.runCalc()
}
} label: {
Text("Calculer")
}
... *// Here I can show and see the calculated vMoyenne property without problem...*
...
}
And the PassageView.swift where I want to show the vMoyenne property...
struct PassageView: View {
#ObservedObject var parameters:Parameters
var body: some View {
Text("\(parameters.vMoyenne)") *//want to show the vMoyenne value that we calculate previously but it always show 0,000...*
}
}
Thanks a lot for your help !!
PS : I tried many things like using didSet but I don't understand what I did wrong...
I found some post on stackoverflow but when I tried it doesn't work...
If you update the ContentView to it should work. The problem was that the SpeedView and PassageView were not sharing the same parameters object
struct ContentView: View {
#StateObject var parameters: Parameters = .init()
var body: some View {
TabView {
SpeedView(parameters: parameters).tabItem {
Label("Vitesse", systemImage: "figure.run.circle.fill")
}
PassageView(parameters: parameters).tabItem {
Label("Passage", systemImage: "timer.circle.fill")
}
}
}
}
Related
I am a newbie to SwiftUI, and I have a simple question, how to update the #State content of a VIEW in another Class, a simulated Code is as follows
When I press the button, the fruits.price variable is not updated in the View. Is there something I'm missing, or is there something wrong I don't understand
class Fruits: ObservableObject {
#Published var price = 1
}
struct ContentView: View {
#ObservedObject var fruits = Fruits()
var extenalClass = ExtenalClass()
var body: some View {
VStack {
Text(String(fruits.price))
.padding()
Button("Add-Me") {
// fruits.price += 1
extenalClass.fChangePrice()
print (fruits.price)
}
}
}
}
class ExtenalClass: ObservableObject {
#ObservedObject var fruits = Fruits()
func fChangePrice() {
fruits.price = 888
print (fruits.price)
}
}
We don't use classes in SwiftUI for model types, we use structs. Any change to the struct is detected by SwiftUI as a change to the state, so body is called to get the new Views, e.g.
struct Fruit {
var price = 1
}
struct ContentView: View {
#State var fruit = Fruit()
var body: some View {
VStack {
Text(fruit.price, format: .currency)
.padding()
Button("Add-Me") {
fruit.price += 1
print (fruit.price)
}
}
}
}
Thanks jnpdx, Baglan for the guidance .... I just found out my answer (probably not the right way), which is to put #Published and "My Function" together in the same CLASS...that is, Function is placed in the CLASS containing #Published...or, another way of saying , put #Published in the CLASS that contains "My Function"
class Fruits: ObservableObject {
#Published var price = 1
// Move (ExtenalClass) Function to here
func fChangePrice() {
price = 888
print (price)
}
}
struct ContentView: View {
#ObservedObject var fruits = Fruits()
// var extenalClass = ExtenalClass()
var body: some View {
VStack {
Text(String(fruits.price))
.padding()
Button("Add-Me") {
// fruits.price += 1
fruits.fChangePrice() // Modified
print (fruits.price)
}
}
}
}
//class ExtenalClass: ObservableObject {
// #ObservedObject var fruits = Fruits()
// func fChangePrice() {
// fruits.price = 888
// print (fruits.price)
// }
//}
I'm having issues pulling data from an Array into a picker using SwiftUI. I can correctly make a list of the data I'm interested in, but can't seem to make the same logic work to pull the data into a picker. I've coded it a few different ways but the current way I have gives this error:
Referencing initializer 'init(_:content:)' on 'ForEach' requires that 'Text' conform to 'TableRowContent'
The code is below:
import SwiftUI
struct BumpSelector: View {
#ObservedObject var model = ViewModel()
#State var selectedStyle = 0
init(){
model.getData2()}
var body: some View {
VStack{
List (model.list) { item in
Text(item.style)}
Picker("Style", selection: $selectedStyle, content: {
ForEach(0..<model.list.count, content: { index in
Text(index.style)
})
})
}
}
The model is here:
import Foundation
struct Bumps: Identifiable{
var id: String
var style: String
}
and the ViewModel is here:
import Foundation
import Firebase
import FirebaseFirestore
class ViewModel: ObservableObject {
#Published var list = [Bumps]()
#Published var styleArray = [String]()
func getData2() {
let db = Firestore.firestore()
db.collection("bumpStop").getDocuments { bumpSnapshot, error in
//Check for errors first:
if error == nil {
//Below ensures bumpSnapshot isn't nil
if let bumpSnapshot = bumpSnapshot {
DispatchQueue.main.async {
self.list = bumpSnapshot.documents.map{ bump in
return Bumps(id: bump.documentID,
style: bump["style"] as? String ?? "")
}
}
}
}
else {
//Take care of the error
}
}
}
}
index in your ForEach is just an Int, there is no style associated with an Int. You could try this approach to make the Picker work with its ForEach:
struct BumpSelector: View {
#ObservedObject var model = ViewModel()
#State var selectedStyle = 0
init(){
model.getData2()
}
var body: some View {
VStack{
List (model.list) { item in
Text(item.style)}
Picker("Style", selection: $selectedStyle) {
ForEach(model.list.indices, id: \.self) { index in
Text(model.list[index].style).tag(index)
}
}
}
}
}
EDIT-1:
Text(model.list[selectedStyle].style) will give you the required style of the selectedStyle.
However, as always when using index, you need to ensure it is valid at the time of use.
That is, use if selectedStyle < model.list.count { Text(model.list[selectedStyle].style) }.
You could also use this alternative approach that does not use index:
struct Bumps: Identifiable, Hashable { // <-- here
var id: String
var style: String
}
struct BumpSelector: View {
#ObservedObject var model = ViewModel()
#State var selectedBumps = Bumps(id: "", style: "") // <-- here
init(){
model.getData2()
}
var body: some View {
VStack{
List (model.list) { item in
Text(item.style)
}
Picker("Style", selection: $selectedBumps) {
ForEach(model.list) { bumps in
Text(bumps.style).tag(bumps) // <-- here
}
}
}
.onAppear {
if let first = model.list.first {
selectedBumps = first
}
}
}
}
Then use selectedBumps, just like any Bumps, such as selectedBumps.style
I try to develop an WatchOS app, where the views are feeded by a timer:
import SwiftUI
import Combine
class AcidityTimer: ObservableObject {
#Published var num: Int = 0
private var subscription: AnyCancellable?
init() {
Timer.scheduledTimer(withTimeInterval: 1.0, repeats: true) { _ in
self.num += 1
if self.num == 101 {
self.num = 0
}
}
}
}
struct AcidityTextView: View {
#EnvironmentObject var acTimer: AcidityTimer
#State var acidity: Double = 0.0
var body: some View {
Text(String(format: "Acidity: %.1f", acidity))
.onReceive(acTimer.$num) { result in
acidity = Double(result) / 10.0
}
}
}
struct AcidityGaugeView: View {
#State var acidity = 0.0
#EnvironmentObject var acTimer: AcidityTimer
var body: some View {
Gauge(value: acidity, in: 0...10) {
Image(systemName: "drop.fill")
.foregroundColor(.green)
} currentValueLabel: {
Text("\(acidity, specifier: "%.1f")")
} minimumValueLabel: {
Text("0")
} maximumValueLabel: {
Text("10")
}
.gaugeStyle(CircularGaugeStyle())
.onReceive(acTimer.$num) { result in
acidity = Double(result) / 10.0
}
}
}
struct ContentView: View {
#ObservedObject var acTimer = AcidityTimer()
#State var counter: Int = 0
var body: some View {
TabView {
AcidityTextView()
.environmentObject(acTimer)
AcidityGaugeView()
.environmentObject(acTimer)
}
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
The app itself runs fine on the Apple Watch simulator, but I get the error message:
[SwiftUI] Accessing State's value outside of being installed on a View. This will result in a constant Binding of the initial value and will not update.
Any idea what's wrong?
You use timer on initial and nowhere didn't stopped or update
You can change implementation to
struct ContentView: View {
#State var timeRemaining = 10
let timer = Timer.publish(every: 1, on: .main, in: .common).autoconnect()
var body: some View {
Text("\(timeRemaining)")
.onReceive(timer) { _ in
if timeRemaining > 0 {
timeRemaining -= 1
}
}
}
}
I came across a situation that you use class data as your data source, and display them in a swiftUI list view, when you update your data source, the swiftUI list view won't be updated, what can we do to make the class data updates interactive with swiftUI?
see code blow:
I define the environment object :
import Foundation
import Combine
class DataSource: ObservableObject {
public static let shared = DataSource()
#Published var datalist: [RowData] = []
func fetch() -> Void {
for n in 1...50 {
let data = RowData(title: "Index:\(n)", count: 0)
datalist.insert(data, at: 0)
}
}
func update() {
for data in datalist {
data.count = data.count+1
print("\(data.title) update count to :\(data.count)")
data.objectWillChange.send()
}
self.objectWillChange.send()
}
}
to display each data in a Row View:
import SwiftUI
struct RowView: View {
#State var data: RowData
var body: some View {
HStack{
Text(data.title)
Spacer()
Text("\(data.count)")
}.padding()
}
}
struct RowView_Previews: PreviewProvider {
static var previews: some View {
RowView(data: RowData(title: "text", count: 1))
}
}
class RowData: ObservableObject {
var title: String = ""
var count: Int = 0
init(title: String, count: Int) {
self.title = title
self.count = count
}
}
in content view, display the data in a list view, I would like to refresh all the view updates when click update button. the button triggers the update methods to update the class data value from data source.
struct ContentView: View {
#EnvironmentObject var data: DataSource
#State var shouldUpdate:Bool = false
#State var localData:[RowData] = []
var body: some View {
VStack {
Button(action: {
// your action here
self.data.update()
self.shouldUpdate.toggle()
self.localData.removeAll()
self.localData = self.data.datalist
}) {
Text("update")
}
List {
ForEach(0..<self.localData.count, id:\.self) { index in
RowView(data: self.localData[index])
}
}
}
}
}
Well... I don't see the reason to have localData, but, anyway, here is modified code that works.
Tested with Xcode 12 / iOS 14
class DataSource: ObservableObject {
public static let shared = DataSource()
#Published var datalist: [RowData] = []
func fetch() -> Void {
for n in 1...50 {
let data = RowData(title: "Index:\(n)", count: 0)
datalist.insert(data, at: 0)
}
}
func update() {
for data in datalist {
data.count = data.count+1
print("\(data.title) update count to :\(data.count)")
}
self.objectWillChange.send()
}
}
struct RowView: View {
#ObservedObject var data: RowData
var body: some View {
HStack{
Text(data.title)
Spacer()
Text("\(data.count)")
}.padding()
}
}
class RowData: ObservableObject {
#Published var title: String = ""
#Published var count: Int = 0
init(title: String, count: Int) {
self.title = title
self.count = count
}
}
struct ContentView: View {
#EnvironmentObject var data: DataSource
#State var localData:[RowData] = []
var body: some View {
VStack {
Button(action: {
// your action here
self.data.update()
self.localData = self.data.datalist
}) {
Text("update")
}
List {
ForEach(0..<self.localData.count, id:\.self) { index in
RowView(data: self.localData[index])
}
}
}
.onAppear {
self.data.fetch()
self.localData = self.data.datalist
}
}
}
I'm trying to fill up a Picker with data fetched asynchronously from external API.
This is my model:
struct AppModel: Identifiable {
var id = UUID()
var appId: String
var appBundleId : String
var appName: String
var appSKU: String
}
The class that fetches data and publish is:
class AppViewModel: ObservableObject {
private var appStoreProvider: AppProvider? = AppProvider()
#Published private(set) var listOfApps: [AppModel] = []
#Published private(set) var loading = false
fileprivate func fetchAppList() {
self.loading = true
appStoreProvider?.dataProviderAppList { [weak self] (appList: [AppModel]) in
guard let self = self else {return}
DispatchQueue.main.async() {
self.listOfApps = appList
self.loading = false
}
}
}
init() {
fetchAppList()
}
}
The View is:
struct AppView: View {
#ObservedObject var appViewModel: AppViewModel = AppViewModel()
#State private var selectedApp = 0
var body: some View {
ActivityIndicatorView(isShowing: self.appViewModel.loading) {
VStack{
// The Picker doesn't bind with appViewModel
Picker(selection: self.$selectedApp, label: Text("")) {
ForEach(self.appViewModel.listOfApps){ app in
Text(app.appName).tag(app.appName)
}
}
// The List correctly binds with appViewModel
List {
ForEach(self.appViewModel.listOfApps){ app in
Text(app.appName.capitalized)
}
}
}
}
}
}
While the List view binds with the observed object appViewModel, the Picker doesn't behave in the same way. I can't realize why. Any help ?
I filed bug report, FB7670992. Apple responded yesterday, suggesting that I confirm this behavior in iOS 14, beta 1. It appears to now have been resolved.
struct ContentView: View {
#ObservedObject var viewModel = ViewModel()
var body: some View {
Picker("", selection: $viewModel.wheelPickerValue) {
ForEach(viewModel.objects) { object in
Text(object.string)
}
}
.pickerStyle(WheelPickerStyle())
.labelsHidden()
}
}
Where
struct Object: Identifiable {
let id = UUID().uuidString
let string: String
}
class ViewModel: ObservableObject {
private var counter = 0
#Published private(set) var objects: [Object] = []
#Published var segmentedPickerValue: String = ""
#Published var wheelPickerValue: String = ""
fileprivate func nextSetOfValues() {
let newCounter = counter + 3
objects = (counter..<newCounter).map { value in Object(string: "\(value)") }
let id = objects.first?.id ?? ""
segmentedPickerValue = id
wheelPickerValue = id
counter = newCounter
}
init() {
let timer = Timer.scheduledTimer(withTimeInterval: 2, repeats: true) { [weak self] timer in
guard let self = self else { timer.invalidate(); return }
self.nextSetOfValues()
}
timer.fire()
}
}
Results in:
I can't put this into your code because it is incomplete but here is a sample.
Pickers aren't meant to be dynamic. They have to be completely reloaded.
class DynamicPickerViewModel: ObservableObject {
#Published private(set) var listOfApps: [YourModel] = []
#Published private(set) var loading = false
fileprivate func fetchAppList() {
loading = true
DispatchQueue.main.async() {
self.listOfApps.append(YourModel.addSample())
self.loading = false
}
}
init() {
fetchAppList()
}
}
struct DynamicPicker: View {
#ObservedObject var vm = DynamicPickerViewModel()
#State private var selectedApp = ""
var body: some View {
VStack{
//Use your loading var to reload the picker when it is done
if !vm.loading{
//Picker is not meant to be dynamic, it needs to be completly reloaded
Picker(selection: self.$selectedApp, label: Text("")) {
ForEach(self.vm.listOfApps){ app in
Text(app.name!).tag(app.name!)
}
}
}//else - needs a view while the list is being loaded/loading = true
List {
ForEach(self.vm.listOfApps){ app in
Text(app.name!.capitalized)
}
}
Button(action: {
self.vm.fetchAppList()
}, label: {Text("fetch")})
}
}
}
struct DynamicPicker_Previews: PreviewProvider {
static var previews: some View {
DynamicPicker()
}
}