lazyloading

Remember, when you use lazy loading, you always have to access the object through its getter method.

for example:

@implementation LocationsViewController
{
    NSFetchedResultsController *_fetchedResultsController;
}

// this is the _fetchedResultsController's getter method,
// use self.fetchedResultsController 
// in other place so we can call this method everytime.
// so the lazy loading working. if we directly 
// use _fetchedResultsController, can not realize lazt loading
- (NSFetchedResultsController *)fetchedResultsController
{
    if (_fetchedResultsController == nil)
    {
       // create the fetchedResultsController
    }
    return _fetchedResultsController;
}

- (void)doSomething
{   
    // we use
    [self.fetchedResultsController doSometing];
    
    // we do not use [_fetchedResultsController doSometing];
    // because we want to use last method to realize lazy loading.
}