threading for network calls in iOS 5

Question

I have been looking over the internet, but could not find the perfect tutorial for threading in iOS, currently i am working on iOS 5 , tutorial found on web were old, my app needs to fetch data from webservices, so I want to call network operation in a thread, I have a tabbar, in each tab it loads different type of data from web, as it start fetching data , I dont want my app to stuck on that tab, i want that user can navigate to other tab meanwhile its fetching data for that tab. how can it be possible

EDIT: I want to have a flow :

 //in a thread
 fetchDataFromWeb(){//during this call activity indicator
 //fetch and make an array of ojbects     
 }

when data is loaded trigger the populate funciton

laoddata(){//remove activity indicator
//load tableview and other views
}

how will i know my thread finished its process

Answer 1

Take a look to NSOperation, NSThread or Grand Central Dispatch

Edit: NSThread example

//on main thread on some action
 NSDictionary *myParameterDitionary = [..];
 [NSThread detachNewThreadSelector:@selector(aBackThreadMethod:) toTarget:self withObject:myParameterDitionary];

//this is on back thread called
- (void)aBackThreadMethod:(NSDictionary *)variablesDictionary{
    @autoreleasepool {
        //presess data
        NSDictionary *responseDictionary = [..];
        [self performSelectorOnMainThread:@selector(didABackThreadMethod:) withObject:responseDictionary waitUntilDone:YES];
    }
}

//call back on main thread
- (void)didFinishABackThreadMethod:(NSDictionary *)responseDictionary{
   //do stuff ex update views
}

The @autoreleasepool is for ARC. If you use manual memory management you have to do:

NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
[pool release];