a day in the life

Now I come from a flex world, so dont hurt me when I say this was a tough thing to figure out for me.  Typically in Flex, you can create handlers fairly easily. Ok, really easily.  For the iPhone, I wanted to basically have the same custom handler “handle” my operation. Hmmm….enter the delegate.

This is a pretty cool technique (fundamental actually) that can be used in your code to “handle” different things throughout your application. So in this exampkle, lets say that you have a UITableViewController that you want to fetch a TON of data.

So I will have two classes I am creating:

- my UITableViewController
- my NSOperation subclass

So here is the code for the NSOperation subclass so you can kind of get a feel for that first.

@interface MyFetchDataOperation : NSOperation
{
// this is our delegate that will handle the results
// of our operation

id   myHandlerDelegate;

}

@property (nonatomic, retain) id     myHandlerDelegate;
@ end
// and here is the .m (implementation file)
// this is just showing the main method override.

@implementation MyFetchDataOperation

@synthesize myHandlerDelegate;
// when subclassing the NSOperation, we simply override the main method
-(void)main
{

// perform my HUGE data fetch here!
......

// on complete of the HUGE data fetch we can now check on the responder and call
// our custom handler!

if( [myHandlerDelegate respondsToSelector:@selector(handleFetchDataOperation:)])
{
[myHandlerDelegate performSelectorOnMainThread:@selector(handleFetchDataOperation:) withObject:myFetchedDataArray waitUntilDone:YES];
}

}

@end

//end

In our subclasses NSOperation you will see the myHandlerDelegate property.  This is what you need to create so that when you instantiate your NSOperation, you can set the myHandlerDelegate to any handling class you want, in this case, it will be our UITableViewController.  Cmon, lets check it out. haha.

@interface MyTableViewController : UITableViewController
{
// we will add our operations to the operationQueue
// to kick them off
NSOperationQueue  *operationQueue;
}
@property (nonatomic, retain) NSOperationQueue  *operationQueue;
@end

@implementation MyTableViewController
@synthesize operationQueue;

-(void)viewDidLoad
{
// init the operationQueue
// in this case I am initializing the operationQueue in my viewController
// but typically you can place this in your AppDelegate, you typically dont need
// a ton of queues!

self.operationQueue = [[NSOperation alloc] init];

}

-(void)fetchMyData
{

MyDataFetchOperation  *fetchOp  = [[MyDataFetchOperation alloc] init];
fetchOp.myHandlerDelegate = self;
[self.operationQueue addOperation:fetchOp];
}
// our custom success handler
// in our operation we are calling a "handleFetchDataOperation" handler, well here it is!

-(void)handleFetchDataOperation:(NSMutableArray *)myFetchedData
{
// handle your complete operation and your data accordingly
}

@end
//end

Now I used to do this with notifications, but well, this seems more proper to me.
any feedback would be cool, and let me know if there is a better way!

Tags: Handler, NSOperation

This entry was posted on Sunday, April 5th, 2009 at 10:17 am and is filed under Code, iphone. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.