How to display ProgressView during an async operation in SwiftUI

Question

Hello! I want to display progress during my operation. I'm new to swift and swiftui. Please help... Here is the model with one async method:

class CountriesViewModel : ObservableObject {
    
    @Published var countries: [String] = [String]()
    @Published var isFetching: Bool = false
    
    @MainActor
    func fetch() async {
        
        countries.removeAll()
        
        isFetching = true
        
        countries.append("Country 1")
        Thread.sleep(forTimeInterval: 1)
        countries.append("Country 2")
        Thread.sleep(forTimeInterval: 1)
        countries.append("Country 3")
        Thread.sleep(forTimeInterval: 1)
        
        isFetching = false
    }
}

and the ContentView:

struct ContentView: View {
    
    @StateObject var countriesVM = CountriesViewModel()
    
    var body: some View {
        ZStack {
            if (countriesVM.isFetching) {
                ProgressView("Fetching...")
            }
            else {
                List {
                    ForEach(countriesVM.countries, id: \.self) { country in
                        Text(country)
                    }
                }
                .task {
                    await countriesVM.fetch()
                }
                .refreshable {
                    Task {
                        await countriesVM.fetch()
                    }
                }
            }
        }
    }
}

The progress is not displayed. What am I doing wrong?

workingdog support Ukraine · Accepted Answer · 2022-05-15 11:42:56Z

4

you could try this simple approach:

struct ContentView: View {
    @StateObject var countriesVM = CountriesViewModel()
    
    var body: some View {
        ZStack {
            if (countriesVM.isFetching) {
                ProgressView("Fetching...")
            }
            else {
                List {
                    ForEach(countriesVM.countries, id: \.self) { country in
                        Text(country)
                    }
                }
                .refreshable {
                    Task {
                        await countriesVM.fetch()
                    }
                }
            }
        }
        .task {  // <-- here
            await countriesVM.fetch()
        }
    }
    
    class CountriesViewModel : ObservableObject {
        
        @Published var countries: [String] = [String]()
        @Published var isFetching: Bool = true  // <-- here
        
        @MainActor
        func fetch() async {
            
            countries.removeAll()
            
            isFetching = true
            
            countries.append("Country 1")
            Thread.sleep(forTimeInterval: 1)
            countries.append("Country 2")
            Thread.sleep(forTimeInterval: 1)
            countries.append("Country 3")
            Thread.sleep(forTimeInterval: 1)
            
            isFetching = false
        }
    }
}

EDIT-1: including a button to refresh the data.

struct ContentView: View {
    @StateObject var countriesVM = CountriesViewModel()
    
    var body: some View {
        
        ZStack {
            if countriesVM.isFetching {
                ProgressView("Fetching...")
            }
            else {
                VStack {
                    Button("refresh", action: {
                        Task { await countriesVM.fetch() }
                    }).buttonStyle(.bordered)
                    List {
                        ForEach(countriesVM.countries, id: \.self) { country in
                            Text(country)
                        }
                    }
                    .refreshable {
                        await countriesVM.fetch()
                    }
                }
            }
        }
        .task {
            await countriesVM.fetch()
        }
    }
    
    class CountriesViewModel : ObservableObject {
        
        @Published var countries: [String] = [String]()
        @Published var isFetching: Bool = false
        
        @MainActor
        func fetch() async {
            countries.removeAll()
            
            isFetching = true
            
            // representative background async process
            DispatchQueue.global(qos: .background).asyncAfter(deadline: .now() + 2) {
                // eventualy, updates on the main thread for the UI to use
                DispatchQueue.main.async {
                    self.countries.append("Country 1")
                    self.countries.append("Country 2")
                    self.countries.append("Country 3")
                    self.isFetching = false
                }
            }
        }
    }
}

edited May 15, 2022 at 11:42

answered May 15, 2022 at 8:53

workingdog support Ukraine

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4 Comments

Viktor Lysenkov Over a year ago

Thanks... Yes, it works... But what if i have a button at ContentView for refreshing data? When i tap the button, no progressview showing...

workingdog support Ukraine Over a year ago

well I cannot second guess what you have and what you have not in your code. All I can do is look at the code of your question. Show the code that truly represents what your problem is, or ask another question with the code you have a problem with.

workingdog support Ukraine Over a year ago

updated my answer with a button to "refresh" the data. P.S, do not use Thread.sleep(forTimeInterval: 1) thinking it simulates a background task.

Viktor Lysenkov Over a year ago

Thanks a lot! That is the needed behaviour! Thread.sleep was used to simulate hard work...

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