```swift
struct ContentView: View {
@ObservedObject var model: Model = Model()
var body: some View {
VStack {
ProgressView("Downloading…", value: model.progress, total: 100)
.onAppear {
Task {
await model.fetchData()
}
}
}
}
}

class Model: ObservableObject {
@Published var progress: Double = 0
func fetchData() async {
for _ in 0...100 {
await MainActor.run { // 加上 onChange 之后会提示 Publishing changes from background threads is not allowed;
progress += 1
}
sleep(1)
}
}
}
```