State Binding issue with UIDocumentPicker object - swiftui

Question

In my SwiftUI App, I have button "Pick A Document", which, when clicked opens a sheet displaying all the available document for user to select. I have a #State #Binding variables setup both in my ContentView and DocumentPicker.
I have onDismiss function in the sheet modifier which gets fired after user has picked a document. Inside onDismiss i am printing the size of the document that user has selected and later i intend to do some operation with the document.
Issue is: When user selects a documents the #State variable does not get updated instantly but it still holds the previous object.
To explain it better, when user clicks the "Pick a Document" for first time at that time State variable has a value of #State var doc: Data = Data() but when user selects a document and sheet is dismissed #Binding variable inside DocumentPicker is updated and SwiftUI must ensure that value is reflected in the Parent View #State Variable. Therefor when onDismiss is called it must print the size of the file that user had selected.
But in reality, it still prints 0 Bytes which is the value given to the #State variable during initialisation.
Now when user again clicks the "Pick a Document" Button and selects another file or the same file that S/he selected last time, now when sheet is dismissed onDismiss method prints the size of the file that user had chosen last time i.e. file selected just before the currently selected file.
Is this expected behaviour if so then how can i get the file returned to my view which user had currently selected?
Here is the complete code:
import SwiftUI
struct ContentView: View {
#State var showSheet = false
#State var doc: Data = Data()
var body: some View {
Button(action: {
showSheet.toggle()
}, label: {
Text("Pick a Document")
}).sheet(isPresented: $showSheet, onDismiss: upload, content: {
DocumentPicker(s3Document: $doc)
})
}
func upload() {
debugPrint("File Size: ", doc)
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
struct DocumentPicker: UIViewControllerRepresentable {
#Binding var s3Document: Data
class Coordinator: NSObject, UINavigationControllerDelegate, UIDocumentPickerDelegate {
var parent: DocumentPicker
init(_ parent: DocumentPicker) {
self.parent = parent
}
func documentPicker(_ controller: UIDocumentPickerViewController, didPickDocumentsAt urls: [URL]) {
let fm = FileManager.init()
if let file = fm.contents(atPath: urls.first!.path) {
parent.s3Document = file
}
}
}
func makeUIViewController(context: UIViewControllerRepresentableContext<DocumentPicker>) -> UIDocumentPickerViewController {
let documentPicker = UIDocumentPickerViewController(forOpeningContentTypes: [.data])
documentPicker.delegate = context.coordinator
documentPicker.allowsMultipleSelection = false
return documentPicker
}
func updateUIViewController(_ uiViewController: UIDocumentPickerViewController, context: UIViewControllerRepresentableContext<DocumentPicker>) {
}
func makeCoordinator() -> Coordinator {
Coordinator(self)
}
}

Answer 1

I have fixed by useing startAccessingSecurityScopedResource()(for more https://developer.apple.com/documentation/foundation/url/1779698-startaccessingsecurityscopedreso).
Change your didPickDocumentsAt method with this. Also, use Data(contentsOf: url) for get file data from the url.
func documentPicker(_ controller: UIDocumentPickerViewController, didPickDocumentsAt urls: [URL]) {
guard let url = urls.first, url.startAccessingSecurityScopedResource() else { return }
defer {
DispatchQueue.main.async {
url.stopAccessingSecurityScopedResource()
}
}
do {
parent.s3Document = try Data(contentsOf: url)
} catch {
print("no data")
}
}
One more thing needs to add inside the upload() function. Add all code inside the DispatchQueue.main.async. Because of this function call before the value assign. You can also use closure in an alternative way.
func upload() {
DispatchQueue.main.async {
debugPrint("File Size: ", doc)
}
}