Question

I am using the included method to return a pointer to a NSMutableDictionary, that is contained in an NSArray. However, the NSMutableArray (theOne) is being created as a non-mutuable NSDictionary. This is a problem because I want to modify the dictionary after retrieving it with this method.

- (NSMutableDictionary*)getMatFromBoutKey:(NSString*) boutKey
{   
    /*
     * Returns the mat object with the provided boutKey.
     * Returns nil if no mat has that boutKey.
     */

    NSUInteger idx = [[event objectForKey:@"mats"] indexOfObjectPassingTest:
                      ^ BOOL (NSMutableDictionary* obj, NSUInteger idx, BOOL *stop)
                      {
                          return [[obj objectForKey:@"boutKey"] isEqualToString:boutKey];
                      }];

    if (idx == NSNotFound)
        return nil;
    else {
        NSMutableDictionary* theOne = [[event objectForKey:@"mats"] objectAtIndex: idx];
        return theOne;
    }
}

Here’s an image of the debugger stopped on a breakpoint right after the theOne is first referenced.

Why isn’t theOne mutable? How can I return a pointer to the NSMutableDictionary so that I can modify it after I get the value returned to me?

Thanks!

Answer 1

I’m going to assume that you have a dictionary of arrays. Then that array contains a bunch of regular dictionaries. So when you pull it out of the array it is still a regular dictionary regardless of what you assign it to.

For instance, take the following code for example

NSDictionary *dict = [[NSDictionary alloc] init];
NSMutableDictionary *mutDict = dict;

mutDict will contain a regular dictionary because it has not properly been casted to a mutable dictionary.

either make sure when you create the array that is at [event objectForKey:@”mats”] that you put NSMutable dictionaries inside of it OR

use

NSMutableDictionary* theOne = [[[event objectForKey:@"mats"] objectAtIndex: idx] mutableCopy];

When taking the data out