Updating swiftui text view by a function in another file - ios

Question

I have a function that goes out to an API and gets a stock price. When I try to run the function updateView(), I just get 50 instead of 60 which is expected in the text view. The function updateView() can't change the text. Can someone tell me what I'm doing wrong? My code is below.
struct ContentView: View {
#State var stockPrice: Double = 0.0
var body: some View {
List {
HStack {
Text("Stock Price (15 Min. delay)")
Spacer()
Text("\(stockPrice)")
.onAppear() {
self.updateStockPrice(stock: 50)
}
}
}
}
public func updateStockPrice(stock: Int) {
DispatchQueue.main.asyncAfter(deadline: .now() + 1) {
DispatchQueue.main.async {
self.stockPrice = Double(stock)
}
}
}
}
// Assume function updateView is in another file.
func updateView() {
ContentView().stockPrice = 60.0
}

Answer 1

You have the following three problems with your code:
As pawello2222 mentioned, you need to set stockPrice on the same ContentView object that is being displayed. You will find it either in your AppDelegate or SceneDelegate.
#State does not publish changes. You need a #Published variable in an #ObservableObject.
onAppear() gets called when the view is updated on binding variable change. And so, your value will get overwritten. You need to find another place to call updateStockPrice() - the view initializer perhaps.
The following code snippet works in Playground. But depending on your real-world context, you will have to fix the above problems appropriately.
import SwiftUI
import PlaygroundSupport
class Model: ObservableObject {
#Published var stockPrice: Double = 0.0
}
struct ContentView: View {
#ObservedObject var model = Model()
init() {
self.updateStockPrice(stock: 50)
}
var body: some View {
List {
HStack {
Text("Stock Price (15 Min. delay)")
Spacer()
Text("\(model.stockPrice)")
}
}
}
public func updateStockPrice(stock: Int) {
DispatchQueue.main.asyncAfter(deadline: .now() + 1) {
DispatchQueue.main.async {
self.model.stockPrice = Double(stock)
}
}
}
}
// Assume function updateView is in another file.
func updateView(_ view: ContentView) {
view.model.stockPrice = 60.0
}
let view = ContentView()
updateView(view)
PlaygroundPage.current.setLiveView(view)