popToViewController Executing First - ios

Question

When the post button is pressed, the function below executes. In the function, all the objects that are retrieved using the Parse backend are appended to the groupConversation array, which is a global array. However, when I reference the array in the UITableViewController that is popped to towards the end of the function and use println() to print the content of the array, the array is empty. However, when I use println() in the UIViewController that contains this function the array is shown to contain one object. In the console, the println() of the UITableViewController that is popped to once the button is pressed, is executed before the println() of the UIViewController that contains the function below. How can I make the functon below execute completely before popping to the UITableViewController.
#IBAction func postButtonPressed(sender: AnyObject) {
//Adds Object To Key
var name=PFObject(className:currentScreen)
name["userPost"] = textView.text
name.saveInBackgroundWithBlock {
(success: Bool!, error: NSError!) -> Void in
if success == true {
self.textView.text=""
} else {
println("TypeMessageViewController Error")
}
}
//Gets all objects of the key
var messageDisplay = PFQuery(className:currentScreen)
messageDisplay.selectKeys(["userPost"])
messageDisplay.findObjectsInBackgroundWithBlock {
(objects: [AnyObject]!, error: NSError!) -> Void in
if error == nil{
for object in objects {
var textObject = object["userPost"] as String
groupConversation.append(textObject)
}
} else {
// Log details of the failure
}
println("Type message \(groupConversation)")
}
navigationController!.popToViewController(navigationController!.viewControllers[1] as UIViewController, animated: true)
}

Answer 1

The problem is here messageDisplay.findObjectsInBackgroundWithBlock. As you are doing this in background thread, it will be separated from main thread. And your main thread will execute as it should be.
So it before finishing the task you main thread popping the view.
messageDisplay.findObjectsInBackgroundWithBlock {
(objects: [AnyObject]!, error: NSError!) -> Void in
if error == nil{
for object in objects {
var textObject = object["userPost"] as String
groupConversation.append(textObject)
}
} else {
// Log details of the failure
}
println("Type message \(groupConversation)")
dispatch_async(dispatch_get_main_queue()) {
self.navigationController!.popToViewController(navigationController!.viewControllers[1] as UIViewController, animated: true)
return
}
}
Pushing and popping in background thread may cause problem. So get the main thread after executing the task in background and then pop in main thread.
In swift single statement closures automatically return the statement return value. In your specific case, it's attempting to return an instance of [AnyObject]?, which is the return value of popToViewControllerAnimated. The closure expected by dispatch_afteris Void -> Void instead. Since the closure return type doesn't match, the compiler complains about that.
Hope this helps.. ;)

Answer 2

You are running into a very common issue with asynchronous code. Both your ...InBackgroundWithBlock {} methods run something in the background (async).
The best example I have found to explain it is this:
When you start an async code block, it is like putting eggs on to boil. You also get to include something that should be done when they finish boiling (the block). This might be something like remove the shell and slice the eggs.
If your next bit of code is "butter bread, put eggs on bread" you might get unexpected results. You don't know if the eggs have finished boiling yet, or if the extra tasks (removing shell, slicing) has finished yet.
You have to think in an async way: do this, then when it is finished do this, etc.
In terms of your code, the call to popToViewController() should probably go inside the async block.