CODEWITHSUNDEEP
iphoneobjective-ciosmultithreadinggrand-central-dispatch
Adam Waite
Adam Waite

Reputation: 18845

Asynchronous Process Giving Me Trouble

I want to return information from a turn based game from the game center servers, which is all fine, but I want the player alias which is acquired using the asynchronous method:

[GKPlayer loadPlayersForIdentifiers:singleOpponentArray withCompletionHandler:^(NSArray *players, NSError *error) {

                GKPlayer *returnedPlayer = [players objectAtIndex:0];

                NSString *aliasToAdd = [NSString stringWithString:returnedPlayer.alias];
                NSString *idToAdd = [NSString stringWithString:returnedPlayer.playerID];
                NSDictionary *dictionaryToAddToAliasArray = [NSDictionary dictionaryWithObjects:[NSArray arrayWithObjects:aliasToAdd, idToAdd, nil] forKeys:[NSArray arrayWithObjects:@"alias", @"id", nil]];

                [self.aliasArray addObject:dictionaryToAddToAliasArray];


            }];

But the UI uses this information and it does't arrive in time. How can I make that method execute synchronously on the main thread?

Thanks.

Upvotes: 0

Views: 166

Answers (2)

Max MacLeod
Max MacLeod

Reputation: 26652

Any UI related code must execute on the main thread.

If your app must wait for the asynchronous call to return, then first disable the UI. For example, set userInteractionEnabled = NO on your UIView.

Then, when the asynchronous methods returns, re-enable the UIView.

In the meantime, display some sort of activity indicator, e.g. UIActivityIndicatorView.

Of course, only do the above in a case where you can't perform the task in the background. Never needlessly block the UI. I'm sure you know that already of course but it's worth restating for any people new to the platform that might be reading this.

To invoke on the main thread, use one of the variants of NSObject's performSelectorOnMainThread method. Or, alternatively, queue it on gcd using the main queue by calling the dispatch_get_main_queue function.

Upvotes: 1

nacho4d
nacho4d

Reputation: 45078

You can do this using GCD functions:

// Show an UILoadingView, etc

[GKPlayer loadPlayersForIdentifiers:singleOpponentArray
              withCompletionHandler:^(NSArray *players, NSError *error) {

    // Define a block that will do your thing
    void (^doTheThing)(void) = ^(void){
        // this block will be run in the main thread....
        // Stop the UILoadingView and do your thing here
    };

    // Check the queue this block is called in          
    dispatch_queue_t main_q = dispatch_get_main_queue();
    dispatch_queue_t cur_q = dispatch_get_current_queue();
    if (main_q != cur_q) {
        // If current block is not called in the main queue change to it and then do your thing
        dispatch_async(main_q, doTheThing);
    } else {
        // If current block is called in the main queue, simply do your thing
        doTheThing();
    }
}];

Upvotes: 0

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