Quick glance at NSOperationQueue

Curtis Hard — Mon, 30 Nov 2009 08:59:47 +0000

I was recently having a quick play with threading in COCOA ( because I needed to run some code on another thread ) and stumbled across NSOperationQueue within the docs. Basically, NSOperationQueue handles NSOperation’s, you give it an NSOperation, it will queue it, and run it when it gets to that part in the queue, but the cool thing is … it runs the NSOperation on another thread!

Its really simple to use, to run your own code / class, you ust subclass NSOperation and have a method called main which doesn’t return anything, so … – (void)main {}. main will get invoked when the item gets called, once all your code has done what it was set out to do, you simple have to perform a selector on the main thread and do what ever you like.

All that said and done, its pretty god damn awesome!, if you haven’t had a look at it yet, its worth a go :D.

A simple COCOA Asynchronous image loader class to use in your iPhone app.

Curtis Hard — Sun, 13 Sep 2009 21:18:46 +0000

This isnt a tutorial, this is just some source code that you might find useful. This class will load images in the background so it wont lock your UI up!

Heres the header file :

@interface GGImageLoader : NSObject {
 
	NSURLConnection * connection;
 
	NSURL * url;
 
	NSMutableData * mutData;
 
	UIImage * image;
 
	id delegate;
 
}
 
@property ( nonatomic, retain ) UIImage * image;
 
- (id)initWithURL:(NSURL *)aURL;
- (void)setDelegate:(id)anObject;
- (void)load;
 
@end
 
@protocol GGImageLoaderProtocol
 
@required
- (void)imageLoader:(GGImageLoader *)loader
	   didLoadImage:(UIImage *)anImage;
 
@optional
- (void)imageLoader:(GGImageLoader *)loader
	didReceiveError:(NSError *)anError;
 
@end

and heres the main file :

#import "GGImageLoader.h"
 
 
@implementation GGImageLoader
 
@synthesize image;
 
- (void)dealloc
{
	[super dealloc];
	[url release];
	[connection release];
	[mutData release];
	[image release];
}
 
- (id)initWithURL:(NSURL *)aURL
{
	url = [aURL retain];
	return self;
}
 
- (void)setDelegate:(id)anObject
{
	delegate = anObject;
}
 
- (void)load
{
	// SHOW NETWORK INDICATOR
 
	[UIApplication sharedApplication].networkActivityIndicatorVisible = YES;
 
	// SET UP THE REQUEST
 
	NSURLRequest * request = [[[NSURLRequest alloc] initWithURL:url] autorelease];
 
	// SET UP THE CONNECTION
 
	connection = [[NSURLConnection alloc] initWithRequest:request
												 delegate:self];
 
	// NEW MUT DATA
 
	mutData = [[NSMutableData new] retain];
 
}
 
- (void)connection:(NSURLConnection *)connection
  didFailWithError:(NSError *)error
{
	if( [delegate respondsToSelector:@selector(imageLoader:didReceieveError:)] )
	{
		[delegate imageLoader:self
			  didReceiveError:error];
	}
}
 
- (void)connection:(NSURLConnection *)connection
	didReceiveData:(NSData *)data
{
 
	// APPEND THE DATA
 
	[mutData appendData:data];
}
 
- (void)connectionDidFinishLoading:(NSURLConnection *)aConnection
{
 
	// ONCE LOADED HIDE NETWORK INDICATOR
 
	[UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
 
	// RELEASE THE CONNECTION
 
	[connection release];
 
	// CREATE NEW UIIMAGE FROM THE DATA
 
	image = [[[UIImage alloc] initWithData:mutData] retain];
 
	if( [delegate respondsToSelector:@selector(imageLoader:didLoadImage:)] )
	{
		[delegate imageLoader:self
				 didLoadImage:image];
	}
 
}
 
@end

Its pretty self explanatory, meerly do the following to get it to work..

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GGImageLoader * imageLoader = [[[GGImageLoader alloc] initWithURL:[NSURL URLWithString:@"myimageurlhere"]] retain];
[imageLoader setDelegate:self];
[imageLoader load];

The class also has delegate methods and a protocol to follow, so we know when the image has loaded, you can use the GGImageLoaderProtocol in your header file if you like.

- (void)imageLoader:(GGImageLoader *)imageLoader didReceieveError:(NSError *)anError
{
}
 
- (void)imageLoader:(GGImageLoader *)imageLoader didLoadImage:(UIImage *)anImage
{
	// BE SURE TO RELEASE THE IMAGE LOADER
	[imageLoader release];
}

and thats about it, hope its helps some people out!

If ive made a mistake anywhere in this please say, it was a rush post!

GeekyGoodness » COCOA

Quick glance at NSOperationQueue

A simple COCOA Asynchronous image loader class to use in your iPhone app.