Question

I have a method myButtonAction which performs some heavy calculations, which I need to run on a background thread, while I am loading a view indicating “Task progress” in the main thread. As soon as the, background thread completes executing the method, I need to remove the “task progress” view and load another view in the main thread.

[self performSelectorInBackground:@selector(myButtonAction) withObject:nil];
[self performSelectorOnMainThread:@selector(LoadView) withObject:nil waitUntilDone:YES];

The problem I am facing is that, before myButtonAction completes execution, the LoadView completes its execution. How can I make sure that LoadView starts execution only after myButtonAction completes its execution.

Note: myButtonAction has its method definition in another class.

Answer 1

Use Grand Central Dispatch:

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    [self myButtonAction];
    dispatch_async(dispatch_get_main_queue(), ^{
        [self LoadView];
    });
});

Or, if you want to stay with performSelector methods:

[self performSelectorInBackground:@selector(loadViewAfterMyButtonAction) withObject:nil];

where

- (void)loadViewAfterMyButtonAction
{
    [self myButtonAction];
    [self performSelectorOnMainThread:@selector(LoadView) withObject:nil waitUntilDone:YES];
}