NSOperation: addsubview in the main thread and slowness
drawrect, nsoperation, nsoperationqueue
Solution
To make things work properly we need to forget about NSOperation and use this "trick"
dispatch_queue_t main_queue = dispatch_get_main_queue();
dispatch_async(main_queue, ^{
[self createCustomViews];
dispatch_async(main_queue, ^{
[self addAnotherCustomViewToView];
});
});
Problem
I have implemented the following NSOperation, to draw `N` custom views ``` - (void)main { for (int i=0; i<N; i++) { << Alloc and configure customView #i >> //(customView is a UIView with some drawing code in drawrect) [delegate.view addSubview:customView]; } NSLog(@"Operation completed"); } ``` in the drawRect method of the customView I have ``` - (void)drawRect { <<Drawing code>> NSLog(@"Drawed"); delegate.drawedViews++; if (delegate.drawedViews==VIEWS_NUMBER) { [delegate allViewsDrawn]; } } ``` So the delegate get the notification when all the views are drawn. The problem is that after the "Operation completed" log it takes about 5 seconds before I can see the first "Drawed" log. Why is this happening? And generally speaking, how should I behave in order to find out which line of code is taking so much time being executed? ------ EDIT ------ Sometimes (like 1 out of 10 times) I was getting crashes doing this because I shouldn't call `addsubview` from the NSOperation since it is not thread-safe. So I changed it to: ``` [delegate.view performSelectorOnMainThread:@selector(addSubview:) withObject:customView waitUntilDone:NO]; ``` Now I don't have crashes anymore, but the process takes a very long time to be executed! Like 5 times more than before. Why is it so slow?