How cellForRowAtIndexPath can reuse formatters (to improve scrolling)?

Allocating NSDateFormatter (or NSNumberFormatter) is relatively slow and

cellForRowAtIndexPath runs for every cell.

So, allocating formatters in cellForRowAtIndexPath can be a significant contributor to jerky scrolling.

To smooth scrolling, I tried allocating them outside cellForRowAtIndexPath,

by making them a class variable and allocating them in viewWillAppear and releasing them in viewWillDisappear (see code below).

But that produce leaks in the formatters.

Where is the best place to declare/allocate/release formatters used in cellForRowAtIndexPath?

//in myNavigationViewController.m:
NSDateFormatter *myDateFormatter;                            

-...viewWillAppear...{                       
    if(myDateFormatter){                    //Solution: add this check.
        [myDateFormatter release];
    }
    myDateFormatter = [[NSDateFormatter alloc] init];                          
    [myDateFormatter setDateStyle:NSDateFormatterShortStyle];
    [myDateFormatter setTimeStyle:NSDateFormatterShortStyle];
    if(locale){                             //Solution: add this check.
        [locale release];
    }
    locale = [NSLocale currentLocale];
    [myDateFormatter setLocale:locale];       
}
开发者_如何学运维-...cellForRowAtIndexPath... {
    cell.myDateLabel.text =  [myDateFormatter stringFromDate:_date];            
}

-...viewWillDisappear...{  
//    [myDateFormatter release];             //Solution: remove this line 
}
-...dealloc {
    [myDateFormatter release];               //Solution: add these 2 lines.
    [locale release];
}

It shouldn't leak at all so long as you remember to deallocate it in -dealloc.