NSMutableArray addObject: giving Error

Question

Here is the code what I am trying..

but the thing is when I load the view first time it works.. doesn't give any problem..

but when i try to load view again and call this code.. it gives error on arrMain addObject:

I am trying to look over it but don't find anything..

can anyone please help??

NSUserDefaults *ds = [NSUserDefaults standardUserDefaults];
NSMutableArray *arrMain = [ds objectForKey:@"files"];
int i;

if([arrMain count] > 0)
{
    i = [arrMain count] + 1;

}
else
{
    arrMain = [[NSMutableArray alloc] init];  
    i = 1;
}
NSLog(@"File Name To Be Saved %d.txt",i);

NSArray *sd = [[NSArray alloc] init];
sd = [dict componentsSeparatedByString:@"/"];
NSMutableDictionary *dict1 = [[NSMutableDictionary alloc] init];

[dict1 setObject:[sd objectAtIndex:[sd count] - 1] forKey:@"name"];
NSString *OrgFilename = [sd objectAtIndex:[sd count] - 1];
NSArray *extArr = [[NSArray alloc] init];
extArr = [OrgFilename componentsSeparatedByString:@"."];
NSString *flExt = [extArr    objectAtIndex:1];
[dict1 setObject:[NSString stringWithFormat:@"%d.txt",i,flExt] forKey:@"filename"];

// *** error happens VVVV
[arrMain addObject:dict1];
// *** error happens ^^^^

[ds setObject:arrMain forKey:@"files"];
[ds synchronize];

Answer 1

The problem is you are trying to retrieve a NSMutableArray from the NSUserDefaults . It will not be returning a NSMutableArray , but a NSArray instead. You will want to do:

NSMutableArray *arrMain = [[[ds objectForKey:@"files"] mutableCopy] autorelease];

The reason it "worked" the first time through was arrMain was nil, so you created a valid NSMutableArray , then saved it into the NSUserDefaults . After that, you got a valid object (non-nil), but it wasn't the type you were expecting. Since -[NSUserDefaults objectForKey:] returns a id type, it happily assigned it your NSMutableArray object, even though it wasn't that type.