Get data off completionhandler - FBRequestConnection - facebook

Question

I found a lot of information concerning completionHandlers. However, I don't yet get how to handle it in this case. Maybe you can help me.
I'm trying to get a list of all Facebook friends and store it in an array.
getFacebookFriends
func getFacebookFriends() -> NSMutableArray
{
var retFriendIDs:NSMutableArray = []
FBRequestConnection.startForMyFriendsWithCompletionHandler {
(connection:FBRequestConnection!, result: AnyObject!, error:NSError!) -> Void in
if (error == nil){
var resultdict = result as! NSDictionary
self.data = resultdict.objectForKey("data") as! NSArray
var friendIDs:NSMutableArray = []
for (var i = 0; i < self.data.count; i++) {
let valueDict : NSDictionary = self.data[i] as! NSDictionary
let id = valueDict.objectForKey("id") as! String
friendIDs.addObject(id as String)
}
retFriendIDs = friendIDs
}
}
return retFriendIDs
}
As this is a completionHandler I understand that the return fires before completion of the block. But how do I achieve a return to use the list in this function for example?
findFacebookFriendsInBackend
func findFacebookFriendsInBackend() -> [AnyObject]{
println("findFacebookFriendsInBackend")
var retFriends:[AnyObject] = []
let fbFriends:NSMutableArray = getFacebookFriends()
var friendQuery = PFUser.query()
// look for friends in Parse
friendQuery!.whereKey("fbId", containedIn: fbFriends as [AnyObject])
friendQuery!.findObjectsInBackgroundWithBlock{
(friends, error) -> Void in
if error == nil {
retFriends = friends as [AnyObject]!
}
}
return retFriends
}
And then use it in a simple function like this:
iterateOverFriends
func iterateOverFriends(friends:[AnyObject]!){
for i in friends {
doSomething(i)
}
}
To call
iterateOverFriends(findFacebookFriendsInBackend())

Answer 1

Short answer: You don't. Not possible. With an async method, the result doesn't exist at the time when you return.
You have to adjust your thinking.
Rewrite this method:
func findFacebookFriendsInBackend() -> [AnyObject]{
As something like this instead:
func findFacebookFriendsInBackend(#completion:
(friendsArray: [AnyObject]) -> ())
In the new form it takes a block as a parameter. Write the function so that it invokes the block once it has built the array of friends.
The new call would look like this
findFacebookFriendsInBackend()
{
(friendsArray) -> () in
iterateOverFriends(friendsArray)
}
(When you have a function that takes a closure as the final parameter, you can call it with the closure outside the parenthesis.)
I wrote a long answer, including a working example project, in this thread.