swift: asynch loading function

Question

After 10 years of coding abstinence, I am actually trying a "come back" by developing a little app in swift using parse as backend. So far it ran quite smooth but since a few days, I have got stuck! I hope some one here can help me.

I wrote two methods in my TableViewController that loads the data from parse backend and the local datastore:

    //get data from local Datastore
func fetchAllObjectsFromLocalDatastore() {
    let query: PFQuery = PFQuery(className: "Task")

    query.fromLocalDatastore()

    query.whereKey("delete", equalTo: false)


    query.findObjectsInBackground().continueWithBlock {
        (task: BFTask!) -> AnyObject in
        if let error = task.error {
            print("Error: \(error)")
            return task
        }
        //LOG
        print("Retrieved \(task.result.count)")

        let objects = task.result as? NSArray
        self.taskObjects = objects?.mutableCopy() as! NSMutableArray
        dispatch_async(dispatch_get_main_queue(), {
            self.tableView.reloadData()
        })
        return task
    }
}

//get data from parse and cach it locally
func fetchAllObjects() {

    let query: PFQuery = PFQuery(className: "Task")

    print(PFUser.currentUser()?.username) //log
    query.whereKey("done", equalTo: false)
    // Query for new results from the network
    query.findObjectsInBackground().continueWithSuccessBlock({
        (task: BFTask!) -> AnyObject! in
        print("Retrieved \(task.result.count)")

        return PFObject.unpinAllObjectsInBackground().continueWithSuccessBlock({
            (ignored: BFTask!) -> AnyObject! in
            // Cache new results in local data store
            let objects = task.result as? NSArray
            let temp : BFTask = PFObject.pinAllInBackground(objects as? [AnyObject], withName: "Task")
            self.fetchAllObjectsFromLocalDatastore()
            return temp
        })
    })

}

These two methods run fine, but now I want to improve the app to a bit a more like MVC architecture and add some new features. Therefore, I have tried to put them into a separate class. Here comes now my problem: when I last developed in C threading got quite populär so it was Also my first intention to do the asynchron tasks. Nur when I have researed the Topos I always ended up Reading of blocks and closures. In my understanding (no idea if it's right), I would have to write asynchronous-callbaks that I can do that – right?

I tried different things like shown here Swift: Asynchronous callback but nothing really worked. Here my last approach:

func fetchAllObjects(completion: (update:Bool?)->()) {
    print("CallParse")
    var update = false
    let query: PFQuery = PFQuery(className: "Task")

    print(PFUser.currentUser()?.username) //log
    query.whereKey("done", equalTo: false)
    // Query for new results from the network

    query.findObjectsInBackground().continueWithSuccessBlock({
    (task: BFTask!) -> AnyObject! in
        print("Retrieved \(task.result.count)")

        return PFObject.unpinAllObjectsInBackground().continueWithSuccessBlock({
        (ignored: BFTask!) -> AnyObject! in
            // Cache new results
            let objects = task.result as? NSArray
            let temp : BFTask = PFObject.pinAllInBackground(objects as? [AnyObject], withName: "Task")
            //self.fetchAllObjectsFromLocalDatastore()
            update = true
            return temp
        })
    //TODO: correct update
    })
}

and the call:

 tasklist.fetchAllObjects({(update) -> () in
                print("lalalalal")
                if (update==true) {
                    dispatch_async(dispatch_get_main_queue(), {
                       self.tableView.reloadData()
                    })
                }
            })

.. but it never prints lalala or updates the tableView