Question

I have this code;

for (int i = 0; i<period+1; i++){

    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setDateFormat:@"dd/MM/yyyy"];
    NSDate *newData = [dataToAdd dateByAddingTimeInterval:60*60*24*j];
    j++;
    NSString *data = [dateFormatter stringFromDate:newData];
    [[appDelegate.globalArray objectAtIndex:[name intValue]]addObject:data];

    [dateFormatter release];
}

this code work fine until I go in background.
appDelegate.globalArray is a global array and when I go in background I store it with NSUserDefault

- (void)applicationDidBecomeActive:(UIApplication *)application {

globalArray = [[NSMutableArray alloc] initWithArray:[[NSUserDefaults standardUserDefaults] objectForKey:@"globalArray"]];}

and

- (void)applicationDidEnterBackground:(UIApplication *)application{

[[NSUserDefaults standardUserDefaults] setObject:globalArray forKey:@"globalArray"];}

the loop work fine until I go in background but when I reopen the application and I enter in this loop I have an exception

“NSCFArray insertObject:atIndex:]: mutating method sent to immutable object”

why?

Answer 1

Is globalArrayan array of arrays? If so, then you need to ensure that each array in globalArray is an instance of NSMutableArrayas well. I believe (correct me if I’m wrong) that when you get an array back from NSUserDefaults, you always get an immutable array. The same goes for your nested arrays.

In that case, you could try the following:

- (void)applicationDidBecomeActive:(UIApplication *)application {

    NSArray *temp = [[NSArray alloc] initWithArray:[[NSUserDefaults standardUserDefaults] objectForKey:@"globalArray"]];
    NSMutableArray *result = [[NSMutableArray alloc] initWithCapacity:[temp count]];

    for (NSArray *nestedArray in temp) {
        [result addObject:[NSMutableArray arrayWithArray:nestedArray]];
    }

    // assuming globalArray is a @property retained by your class
    self.globalArray = result;

    [result release];
    [temp release];
}

There may be a more efficient way to do this, but you get my point…