QueueProxy - call delegate methods on a different operation queue. Useful as a replacement for [NSURLConnection setDelegateQueue:]

QueueProxy.h

#import <Foundation/Foundation.h>

@interface QueueProxy : NSProxy

+ (id) proxyForDelegate: (id)delegate onQueue: (NSOperationQueue *)queue;

@end

QueueProxy.m

#import "QueueProxy.h"

@implementation QueueProxy {
	id _delegate;
	NSOperationQueue *_queue;
}

+ (id)proxyForDelegate:(id)delegate onQueue:(NSOperationQueue *)queue;
{
	QueueProxy *result = [self alloc];
	result->_delegate = delegate;
	result->_queue = [queue retain];
	return [result autorelease];
}

- (void)dealloc;
{
	[_queue release];
	[super dealloc];
}

- (id)forwardingTargetForSelector:(SEL)aSelector
{
	if ([[NSOperationQueue currentQueue] isEqual: _queue]) {
		return _delegate;
	}
	
	return nil;
}

- (void)forwardInvocation:(NSInvocation *)invocation;
{
	[invocation retainArguments];
	[invocation setTarget: self->_delegate];
	NSInvocationOperation *operation = [[NSInvocationOperation alloc] initWithInvocation: invocation];
	[self->_queue addOperation: operation];

	NSMethodSignature *signature = invocation.methodSignature;
	if (strcmp( signature.methodReturnType, @encode( void ) ) != 0) {
		[operation waitUntilFinished];
	}

        [operation release];
}

- (BOOL)respondsToSelector:(SEL)aSelector;
{
	if ([super respondsToSelector: aSelector]) return YES;

	return [_delegate respondsToSelector: aSelector];
}

- (NSMethodSignature *)methodSignatureForSelector:(SEL)sel;
{
	return [_delegate methodSignatureForSelector: sel];
}

- (BOOL)conformsToProtocol:(Protocol *)aProtocol;
{
	if ([super conformsToProtocol: aProtocol]) return YES;

	return [_delegate conformsToProtocol: aProtocol];
}

@end