NSMutableDictionary issues

Question

I'm trying to insert an object in my dictionary, but first, I want to test if it's a NSMutableDictionary :

if ([[[self.response objectForKey:@"X"] objectAtIndex:0] isKindOfClass:[NSMutableDictionary class]]) {
        [[[self.response objectForKey:@"X"] objectAtIndex:0]setObject:@"Hello" forKey:@"Y"];
    }

I get this issue :

*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: '-[__NSCFDictionary setObject:forKey:]: mutating method sent to immutable object'

Look at the doc of `isKindOfClass`, there is a beautiful example with the "NOT TO DO THIS" which matches your issue. — Larme, Mar 14 '14 at 10:29
Try this: `id dictionary = [[self.response objectForKey:@"X"] objectAtIndex:0]; if ([dictionary isKindOfClass:[NSMutableDictionary class]]) { [dictionary setObject:@"Hello" forKey:@"Y"];`. This more readable. } — bsarr007, Mar 14 '14 at 10:35
@whitewolf09 sure, but this would help readers! And improve his question. — bsarr007, Mar 14 '14 at 10:38
@bsarr007 that's why there's an EDIT button in the question section itself. :) — Rukshan, Mar 14 '14 at 10:39
@whitewolf09 I agree with you but i can't really change his code before he test it programmatically inside his program, this is not typo! — bsarr007, Mar 14 '14 at 10:41
check `NSLog(@"%@",[[[self.response objectForKey:@"X"] objectAtIndex:0] class]);` what it prints. — Anoop Vaidya, Mar 14 '14 at 10:43
Well this is wrong to do so.... You should make a `mutableCopy` of this then you can update it. It is getting crash because of immutable object. `NSMutableDictionary *dict = [[[self.response objectForKey:@"X"] objectAtIndex:0] mutableCopy]; [dict setObject:@"Hello" forKey:@"Y"];` — TheTiger, Mar 14 '14 at 10:49

score 3 · Answer 1 · answered Mar 14 '14 at 10:41

3

You can check for the same selector which is crashing,

if([object respondsToSelector:@selector(setObject:forKey:)]) {
    //If YES, it is NSMutableDictionary
}
else { 
    //Not mutable
}

Hope that helps!

answered Mar 14 '14 at 10:41

Amar

13,202
7
53
71

score 2 · Accepted Answer · answered Mar 14 '14 at 10:31

2

Use isMemberOfClass instead of isKindOfClass

answered Mar 14 '14 at 10:31

Rukshan

7,902
6
43
61

Why this should work and no the isKindOfClass, can you be more explicit? – bsarr007 Mar 14 '14 at 10:36
1

Because NSDictionary is a cluster class. ie Although you call it an NSDictionary / NSMutableDictionary, what you are actually given by the initializer (or instance type) is an undocumented subclass.. do some reading on class clusters. NSArray is another – Jef Mar 14 '14 at 12:09

score 1 · Answer 3 · answered Mar 14 '14 at 10:44

Try this,

if ([[[self.response objectForKey:@"X"] objectAtIndex:0] isKindOfClass:[NSDictionary class]]) {

    NSMutableDictionary *dict = [NSMutableDictionary dictionaryWithDictionary:[[self.response objectForKey:@"X"] objectAtIndex:0]];
    [dict setObject:@"Hello" forKey:@"Y"];
    NSMutableArray *xArray = [NSMutableArray arrayWithArray:[self.response objectForKey:@"X"]];
    [xArray replaceObjectAtIndex:0 withObject:dict];
    [self.response setObject:xArray forKey:@"X"];
}

Yes, This is correct answer. I don't think that `isKindOfClass:` is needed here. — TheTiger, Mar 14 '14 at 10:51

NSMutableDictionary issues

3 Answers3