Question

I create a new thread from a controller like this:

[NSThread detachNewThreadSelector:@selector(makeMovie) toTarget:movieMaker withObject:nil];

What is the best way to call methods on the controller from the new thread/movieMaker object?

Answer 1

In this case, you probably want to use the delegate pattern. In your movie-maker class’s .h file:

@protocol MovieMakerDelegate;

@interface MovieMaker : NSObject
{
    id<MovieMakerDelegate> delegate;

    ...
}

@property (nonatomic, assign) id<MovieMakerDelegate> delegate;

...

@end

@protocol MovieMakerDelegate <NSObject>
- (void)movieMaker:(MovieMaker *)maker didSomething:(id)result;
@end

…and in its .m:

@implementation MovieMaker

@synthesize delegate;

...

- (void)makeMovie
{
    NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

    ...

    [self performSelectorOnMainThread:@selector(notifyDelegateOfDoingSomethingWithObject:) withObject:someObject waitUntilDone:YES];

    [pool release];
}

- (void)notifyDelegateOfDoingSomethingWithObject:(id)someObject
{
    [self.delegate movieMaker:self didSomething:someObject];
}

...

@end

Then in your controller’s header, declare that it supports the MovieMakerDelegate protocol, like this:

@interface MyController : Whatever <MovieMakerDelegate>

and in your .m, before calling your -detachNewThreadSelector:etc:, call movieMaker.delegate = self;. Implement the -movieMaker:didSomething: method on your controller class and you’re good to go.