NSOperationQueue mainQueue vs performSelectorOnMainThread?

Question

What's the difference between this:

[[NSOperationQueue mainQueue] addOperationWithBlock:^{
    [self doSomthing:object];
}];

and this:

[self performSelectorOnMainThread:@selector(doSomething:) withObject:object waitUntilDone:NO]

Answer 1

[self performSelectorOnMainThread:@selector(doSomething:) 
                       withObject:object 
                    waitUntilDone:NO]

Will perform the selector right when it is called. This is what you have to use if you want to affect the UI from a background thread. If you say YES to waitUntilDone it will block the thread until the method has completed.

mainQueue adds that block to the operation queue of the mainthread but does not guarantee when it will be executed. There could be other items in that queue still waiting to execute.