CODEWITHSUNDEEP
iphoneobjective-ciosmultithreadingqueue
Andreas
Andreas

Reputation: 167

Updating UI components from an async callback (dispatch_queue)

how can i update GUI elements with values from a queue? if i use async queue construct, textlable don't get updated. Here is a code example i use:

- (IBAction)dbSizeButton:(id)sender {
    dispatch_queue_t getDbSize = dispatch_queue_create("getDbSize", NULL);
    dispatch_async(getDbSize, ^(void)
    {
        [_dbsizeLable setText:[dbmanager getDbSize]]; 
    });

   dispatch_release(getDbSize);
}

Thank you.

Upvotes: 2

Views: 3168

Answers (2)

ferostar
ferostar

Reputation: 7082

As @MarkGranoff said, all UI needs to be handled on the main thread. You could do it with performSelectorOnMainThread, but with GCD it would be something like this:

- (IBAction)dbSizeButton:(id)sender {

    dispatch_queue_t getDbSize = dispatch_queue_create("getDbSize", NULL);
    dispatch_queue_t main = dispatch_get_main_queue();
    dispatch_async(getDbSize, ^(void)
    {
        dispatch_async(main, ^{ 
            [_dbsizeLable setText:[dbmanager getDbSize]];
        });
    });

    // release
}

Upvotes: 9

Mark Granoff
Mark Granoff

Reputation: 16938

Any UI update must be performed on the main thread. So your code would need to modified to use the main dispatch queue, not a queue of your own creation. Or, any of the performSelectorOnMainThread methods would work as well. (But GCD is the way to go, these days!)

Upvotes: 2

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