implementation of NSMetadataQuery along with UIDocuments in swiftUI - swift

Question

I am trying to make a document based app in swiftUI with a custom UI. I want iCloud capabilities in my app. I am trying to use iCloud Document (No cloudKit) way for storing data on iCloud container. I am using UIDocument and it's working. It's storing data to iCloud and I am able to retrieve it back.
Now the thing is when I run the app on two devices (iphone and iPad) and make changes to a file on one device, the changes are not reflecting on the other device while the file or say app is open. I have to close the app and relaunch it to see the changes.
I know I have to implement NSMetadataQuery to achieve this but I am struggling with it. I don't know any objective-C. I have been searching on the internet for a good article but could not find any. Can you please tell how do I implement this feature in my app. I have attach the working code of UIDocument and my Model class.
Thank you in advance !
UIDocument
class NoteDocument: UIDocument {
var notes = [Note]()
override func load(fromContents contents: Any, ofType typeName: String?) throws {
if let contents = contents as? Data {
if let arr = try? PropertyListDecoder().decode([Note].self, from: contents) {
self.notes = arr
return
}
}
//if we get here, there was some kind of problem
throw NSError(domain: "NoDataDomain", code: -1, userInfo: nil)
}
override func contents(forType typeName: String) throws -> Any {
if let data = try? PropertyListEncoder().encode(self.notes) {
return data
}
//if we get here, there was some kind of problem
throw NSError(domain: "NoDataDomain", code: -2, userInfo: nil)
}
}
Model
class Model: ObservableObject {
var document: NoteDocument?
var documentURL: URL?
init() {
let fm = FileManager.default
let driveURL = fm.url(forUbiquityContainerIdentifier: nil)?.appendingPathComponent("Documents")
documentURL = driveURL?.appendingPathComponent("savefile.txt")
document = NoteDocument(fileURL: documentURL!)
}
func loadData(viewModel: ViewModel) {
let fm = FileManager.default
if fm.fileExists(atPath: (documentURL?.path)!) {
document?.open(completionHandler: { (success: Bool) -> Void in
if success {
viewModel.notes = self.document?.notes ?? [Note]()
print("File load successfull")
} else {
print("File load failed")
}
})
} else {
document?.save(to: documentURL!, for: .forCreating, completionHandler: { (success: Bool) -> Void in
if success {
print("File create successfull")
} else {
print("File create failed")
}
})
}
}
func saveData(_ notes: [Note]) {
document!.notes = notes
document?.save(to: documentURL!, for: .forOverwriting, completionHandler: { (success: Bool) -> Void in
if success {
print("File save successfull")
} else {
print("File save failed")
}
})
}
func autoSave(_ notes: [Note]) {
document!.notes = notes
document?.updateChangeCount(.done)
}
}
Note
class Note: Identifiable, Codable {
var id = UUID()
var title = ""
var text = ""
}

Answer 1

This is a complex topic. Apple do provide some sample swift code, the Document-Based App Programming Guide for iOS and iCloud Design Guide.
There is also some good third party guidance: Mastering the iCloud Document Store.
I would recommend reading the above, and then return to the NSMetaDataQuery API. NSMetaDataQuery has an initial gathering phase and a live-update phase. The later phase can remain in operation for the lifetime of your app, allowing you to be notified of new documents in your app's iCloud container.