Is observeValueForKeyPath always called from the main thread?

Question

Is observeValueForKeyPath always called from the main thread?

I'm logging calls with

-(void) observeValueForKeyPath:(NSString *)keyPath
                      ofObject:(id)object
                        change:(NSDictionary *)change
                       context:(void *)context
{
    NSLog(@"KVO: isMainThread %d", [NSThread isMainThread]);
    // ...
}

and it seems to be printing 1 every time, but I was unable to find any guarantee of this in the docs. Can anyone confirm this is the case?

Answer 1

In general, no.

You receive observeValueForKeyPath:ofObject:change:context: on the thread which changed the value. The setter method that changes the value sends the message to all observers after updating the value and before returning.

If you only call the setter on the main thread, then you will only observe the change on the main thread.