Add date to MKAnnotation title property

I'm following the Nerd Ranch i0S Programming guide. I need to tag map annotations with the dates that they were created.

The following method I created overrides the MKAnnotation title property:

- (void)setTitle:(NSString *)t
{
    NSDate *today = [NSDate date];
    NSDateFormatter *dateFormatter = [[[NSDateFormatter alloc] init] autorelease];

    // Obtain copy of passed title.
    [t retain];
    [title release];

    // Set required date format.
    [date开发者_运维百科Formatter setDateFormat:@"dd-MM-yyyy"];

    title = [NSString stringWithFormat:@"%@ %@", t, [dateFormatter stringFromDate:today]];
}

The app crashes at the last line of this method. Can someone please help?

NSString’s +stringWithFormat returns an autoreleased object—since nothing else is taking ownership of it, your title is getting deallocated at the end of the run-loop cycle. You need to call retain on the new value of title, like this:

title = [[NSString stringWithFormat:@"%@ %@", t, [dateFormatter stringFromDate:today]] retain];

or, alternatively, set it to a newly-allocated instance (hence not an autoreleased one), like this:

title = [[NSString alloc] initWithFormat:@"%@ %@", t, [dateFormatter stringFromDate:today]];

I'm not sure, but would it help if you replaced the line

[dateFormatter setDateFormat:@"dd-MM-yyyy"]; 

with

[dateFormatter setDateFormat:[NSString stringWithFormat:@"dd-mm-yyyy"]];