Question

I create an NSMutableArray as follows (note that winner is an instance variable):

winner = [NSMutableArray arrayWithObjects:@"11", @"12", @"13", nil];

When I set winner to nil or remove its objects like

[self.winner removeAllObjects];

my program will automatically shut down. How should I solve this?

Updated !!!
In case I code like this

self.winner = [NSMutableArray arrayWithObjects:@"11", @"12", @"13", nil];

it will call setter method which is

- (void)setWinner:(NSMutableArray *)newWinner
{
    [winner release];
    winner = [newWinner retain];
}

Do I still need to retain the array like

self.winner = [[NSMutableArray arrayWithObjects:@"11", @"12", @"13", nil] retain];

Answer 1

Are you calling -removeAllObjects in a different method? If so, then the problem is likely that you’ve failed to retain the array, and it has been destroyed between the assignment and your later reference. +arrayWithObjects returns an instance that has had autorelease called on it.

Either use a synthesized property to set the instance variable, use a method that returns ownership of the object (like +alloc), or add a retain call:

winner = [[NSMutableArray arrayWithObjects:@"11", @"12", @"13", nil] retain];