Swift Background Sync Manager - ios

Question

I want to make an Upload Manager Singleton that uploads multipart data every 10 minutes. The upload itself is clear but how can i make a class that uploads the data in this time interval in background?
Just to specify:
The data that I want to upload is a model that has an array of objects. Each of the objects has a flag and when this flag is set the object is ready for the upload. That whole "Sync-function" should be called once and repeat itself every 10 minutes, no matter on which ViewController I am. Does anyone know how I can do this?

Answer 1

The code uses some external frameworks. It is based on recursion.
Alamofire // for networking
*The above framework is not important. I just used it to fasten the development process.
Sync Manager
import Foundation
import Alamofire
let SyncMangerIdentifier = "com.example.background.syncmanger"
class SyncManager: Alamofire.Manager{
static let instance = SyncManager()
private var pendingTasks = [SyncTask]() // SyncTask is a class with 3 variables [image,audio,[tags]] that are being uploading to server
private var request: Request?
private var isSyncing = false
private init(){
let configuration = NSURLSessionConfiguration.backgroundSessionConfigurationWithIdentifier(SyncMangerIdentifier)
configuration.allowsCellularAccess = Config.cellularAccess
super.init(configuration: configuration)
}
// CALL THIS FUNCTION TO START THE SYNC
// variable isSyncing guards multiple execution of syncManager
func start(){
guard !isSyncing else {
// WE ARE ALREADY SYNCING
return
}
// CALL TO PREPARE FUNCTION TO EVALUATE WHETHER WE CAN SYNC OR NOT
prepare()
}
/*
initialize the syncItem variable with the first entry from SyncTask
if we are stopping return
if syncTask isEmpty stop
if there are no items in first syncTask remove the task and restart the process.
*/
private func prepare(){
// I use a database query to store & retrieve pendingTasks
guard !pendingTasks.isEmpty else{
// todo no more data to sync
isSyncing = false // syncing process ended
// Notify app that your long running task has finished
(UIApplication.sharedApplication().delegate as? AppDelegate)?.endBackgroundSyncTask()
return
}
isSyncing = true // we are in syncing process
// Notify app that our long running task has begun
(UIApplication.sharedApplication().delegate as? AppDelegate)?.beginBackgroundRestoreTask()
// Call function to start the first upload
uploadFileOrData()
}
}
/**
upload the files & data from array recursively
*/
private func uploadFileOrData(){
var task = pendingTasks[0]
let imageUrl = task.imageUrl
let audioUrl = task.audioUrl
let tags = task.tags.reduce(""){ prev, next in
if prev.isEmpty{
return next.text
}
return "\(prev),\(next.text)"
}
let form : (MultipartFormData) -> () = { data in
if imageUrl.checkResourceIsReachableAndReturnError(nil){
data.appendBodyPart(fileURL: imageUrl, name: "image")
}
if audioUrl.checkResourceIsReachableAndReturnError(nil){
data.appendBodyPart(fileURL: audioUrl, name: "audio")
}
data.appendBodyPart(data: tags.dataUsingEncoding(NSUTF8StringEncoding,allowLossyConversion: false)!, name: "tags")
}
upload(.POST, Api.fileUploadUrl, multipartFormData: form ,encodingCompletion: {
// Call function to process the response
self.processUploadFileResponse($0)
})
}
private func processUploadFileResponse(result: Manager.MultipartFormDataEncodingResult){
switch result {
case .Success(let upload, _, _):
// PERFORM ACTION ON SUCCESS
// MOVE TO NEXT LOCATION
self.moveToNextTask()
case .Failure(_):
// PERFORM ACTION ON FALIURE
// MOVE TO NEXT LOCATION
self.moveToNextTask()
}
}
private func moveToNextTask(){
// DELETE pendingTasks[0] & CALL prepare() function
// If you want to repeat after every 10 MINUTE
// Then wrap your function call 'prepare()' inside dispatch_after
dispatch_after(
dispatch_time(
DISPATCH_TIME_NOW,
Int64(10 * 60 * Double(NSEC_PER_SEC)) // 10 * 60 to convert seconds into minute
),
dispatch_get_main_queue(), {
self.prepare()
})
}
AppDelegate class
// bind the alamofire backgroundCompletionHandler
func application(application: UIApplication, handleEventsForBackgroundURLSession identifier: String, completionHandler: () -> Void) {
// NSLog("handle events for background: \(identifier)")
if identifier == SyncMangerIdentifier{
SyncManager.instance.backgroundCompletionHandler = completionHandler
}
}
// Identifier for long running background task for SyncManager class
var backgroundSyncTask: UIBackgroundTaskIdentifier?
// Call this at the beginning of syncing
func beginBackgroundSyncTask() {
backgroundRestoreTask = UIApplication.sharedApplication().beginBackgroundTaskWithExpirationHandler({
self.endBackgroundRestoreTask()
})
}
// Call this when syncing process ends
func endBackgroundSyncTask() {
guard backgroundSyncTask != nil else {
return
}
UIApplication.sharedApplication().endBackgroundTask(self.backgroundSyncTask!)
self.backgroundSyncTask = UIBackgroundTaskInvalid
}
Note
In order to continue request when your app enters background you may need to enable BackGroundFetchMode from app's Capabilities section

Answer 2

Since you want the method of upload to be called in all ViewControllers(VCs) One approach would be :-
extension UIViewController
{
func uploadData(parameters) ->Bool
{
return true/false;
}
}
Then in all ViewControllers(VCs) you can call uploadData method in viewDidLoad or in specific function like :-
if(self.uploadData(parameters)) // if true method is called i.e. new objects available to upload or 10mins have passed as per your requirement
{
}
Second Approach would be to define the NSTimer part which checks whether 10 mins have passed in AppDelegate and create a empty Swift file which does Upload and call the method in didFinishLaunchingWithOptions within AppDelegate.
There are many ways to go about it but it depends on how flow needs to happen in your app.
Note:- Use
NSURLSessionUploadTask - > To upload and
NSTimer -> To check whether 10 mins have passed