How to get a tableview's data in the background?

Question

I have a background task (usingParse.com API) that fetches and calculates the data for a tableview:

 var usedMessages = [String]()
 var currentMessages = [Message]()

func getCurrentMessages() {

 if currentUser != nil {
  var entryQuery = Entry.query()
  entryQuery.whereKey("user", equalTo: currentUser)
  entryQuery.whereKey("originatedFromType", equalTo: "message")
  entryQuery.findObjectsInBackgroundWithBlock { (entryObjects: [AnyObject]!, getEntriesError: NSError!) -> Void in

   for object in entryObjects {
    var entry = object as Entry
    usedMessages.append(entry.originatedFromId)
   }

   var messageQuery = Message.query()
   messageQuery.whereKey("endDate", greaterThan:NSDate())
   messageQuery.findObjectsInBackgroundWithBlock { (objects: [AnyObject]!, error: NSError!) -> Void in
    for object in objects {
     var message = object as Message
     if !contains(usedMessages, message.objectId) {
      currentMessages.append(message)
     }
    }
    self.tableview.reloadData()
   }
  }
 }
}

Is this the correct way to handle fetching data for a tableview and then reloading the tableviews data? Or should I use a delegate that notifies the tableview that data has changed? or maybe even query.findObjectInBackgroundWithTarget and send the results?

Answer 1

You should always make sure that the reloadData and any UI updates happen in the main thread. Also check if the method does not return an error.

messageQuery.findObjectsInBackgroundWithBlock { (objects: [AnyObject]!, error: NSError!) -> Void in

    if (error == nil)
    {
         //Your code.
        dispatch_async(dispatch_get_main_queue(),{ () -> Void in
            self.tableView.reloadData()
        })
    }
    else
    {
        // Log the error
    }
}