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Editorial Team
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Asked: 2026-05-16T11:12:53+00:00

Hey, I have a problem in Multithreading. To describe this, I have two threads.

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Hey, I have a problem in Multithreading.
To describe this, I have two threads.
On main thread I have some logic
And on another thread, I have a logic and some logic to UI which will update UI.
What I want to do is that I want to call some method after the UI on another thread is updated.
I think I am supposed to use NSOperationQueue or something. or background queue.
but I have read the concurrency programming and threading guide and I still have no idea how to do it.

So how to do it so that I can call a method after a thread is finished?
thanks!

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1 Answer

  1. Editorial Team

    You should never touch the UI from any thread other than the main thread. Two easy ways of sending messsages between threads:

    performSelector:

    [someObject performSelectorOnMainThread:@selector(someSelector) withObject:nil waitUntilDone:NO];

    Notifications:

    NSNotification *notification = [NSNotification notificationWithName:@"myNotification" object:nil];
[[NSNotificationCenter defaultCenter] performSelectorOnMainThread:@selector(postNotification:) withObject:notification waitUntilDone:NO];

    You can of course also use an NSOperationQueue and Key-Value-Observe the job’s finished property, but unless you’d need it for other reasons it just adds unnecessary complexity.

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