Updating a Progress Value in SwithUI - ios

Question

I am trying to update a progress bar using the DispatchQueue.main.async (based on #Asperi's reply at but this does not work! Update progress value from fileImporter modifier in SwiftUI). The problem I am having is the progress updates waits until end of the task and then updates the progress bar which is not the expected behavior.
I put the file processing code within DispatchQueue.global().async, which executes the code right away and updates the Progress bar immediately (goes to 100% instantly) but the file processing task is still not complete. How do I get this to work the right way. Below is the code I am executing. Appreciate your help
Below is the ContentView:
struct ContentView: View {
#ObservedObject var progress = ProgressItem()
#State var importData: Bool = false
var body: some View {
VStack {
Button(action: {importData = true}, label: {Text("Import Data")})
.fileImporter(isPresented: $importData, allowedContentTypes: [UTType.plainText], allowsMultipleSelection: false) { result in
do {
guard let selectedFile: URL = try result.get().first else { return }
let secured = selectedFile.startAccessingSecurityScopedResource()
DispatchQueue.global().async { // added this to import file asynchronously
DataManager(progressBar: progress).importData(fileURL: selectedFile)
}
if secured {selectedFile.stopAccessingSecurityScopedResource()}
} catch {
print(error.localizedDescription)
}
}
ProgressBar(value: $progress.progress, message: $progress.message).frame(height: 20)
}
}
}
ProgressBar View:
struct ProgressBar: View {
#Binding var value: Double
#Binding var message: String
var body: some View {
GeometryReader { geometry in
ZStack(alignment: .leading) {
Rectangle().frame(width: geometry.size.width , height: geometry.size.height)
.opacity(0.3)
.foregroundColor(Color(UIColor.systemTeal))
Rectangle().frame(width: min(CGFloat(self.value)*geometry.size.width, geometry.size.width), height: geometry.size.height)
.foregroundColor(Color(UIColor.systemBlue))
.animation(.linear)
//Text("\(self.value)")
}.cornerRadius(45.0)
}
}
}
DataManager that processes the file. Right now I have a thread.sleep(0..001) to simulate reading of the file
class DataManager {
#Published var progressBar: ProgressItem? = nil
init(progressBar: ProgressItem? = nil) {
self.progressBar = progressBar
}
func importData(fileURL: URL, delimeter: String = ",") {
let lines = try! String(contentsOf: fileURL, encoding: .utf8).components(separatedBy: .newlines).filter({!$0.isEmpty})
let numlines = lines.count
for index in 0..<numlines {
let line = String(lines[index])
Thread.sleep(forTimeInterval: 0.001)
print("\(line)")
DispatchQueue.main.async { // updating the progress value here
self.progressBar?.progress = Double(index)/Double(numlines) * 100
self.progressBar?.message = line
}
}
}
}
ProgressItem:
class ProgressItem: ObservableObject {
#Published var progress: Double = 0
#Published var message: String = ""
}