TouchJSON serializing a structure of dictionaries and arrays

Question

iPhone development question (ObjectiveC).

I'm trying to use TouchJSON library, and having some trouble serialising to JSON. I have ARC switched on so I'm using the ARC branch from github. I'm trying what I imagine to be a fairly a basic nested structure. Three dictionaries inside and array inside a dictionary.

//Make some dictionaries with simple string pairs
NSDictionary *dicA = [NSDictionary dictionaryWithObjectsAndKeys:@"x", @"1", @"y", @"2", nil];
NSDictionary *dicB = [NSDictionary dictionaryWithObjectsAndKeys:@"x", @"1", @"y", @"2", nil];
NSDictionary *dicC = [NSDictionary dictionaryWithObjectsAndKeys:@"x", @"1", @"y", @"2", nil];

//Make an array of dictionary objects
NSArray *saveArray = [NSArray arrayWithObjects:dicA, dicB, dicC, nil];

//Make dictionary which has that array as one of the values
NSDictionary *bigDic = [NSDictionary dictionaryWithObjectsAndKeys:@"arr", saveArray,
                                                                  @"mmm", @"nnn", nil];

NSData *jsonData = [[CJSONSerializer serializer] serializeObject:saveArray error:NULL];
//This works '[{"1":"x","2":"y"},{"1":"x","2":"y"},{"1":"x","2":"y"}]'

NSData *jsonDataB = [[CJSONSerializer serializer] serializeObject:bigDic error:NULL];
//This fails

When I try to serialize bigDic it bombs out at runtime with the following:

'NSInvalidArgumentException', reason: '-[__NSArrayI UTF8String]: unrecognized selector sent to instance

Serializing an array on the line above seems to work OK. What's wrong with my bigDic?

Answer 1

After carefully writing out this question I realised where I had gone wrong. Thought I'd post this anyway. Maybe it's a helpful example for others. So the answer is...

I have my dictionaries back to front!

The dictionaryWithObjectsAndKeys method expects the values and keys the other way around so the correct way to build this structure is:

//Make some dictionaries with simple string pairs
NSDictionary *dicA = [NSDictionary dictionaryWithObjectsAndKeys:@"1", @"x", @"2", @"y", nil];
NSDictionary *dicB = [NSDictionary dictionaryWithObjectsAndKeys:@"1", @"x", @"2", @"y", nil];
NSDictionary *dicC = [NSDictionary dictionaryWithObjectsAndKeys:@"1", @"x", @"2", @"y", nil];

//Make an array of dictionary objects
NSArray *saveArray = [NSArray arrayWithObjects:dicA, dicB, dicC, nil];

//Make dictionary which has that array as one of the values
NSDictionary *bigDic = [NSDictionary dictionaryWithObjectsAndKeys:saveArray, @"arr",
                                                                  @"nnn", @"mmm", nil];

This makes sense when you look at the method name "dictionaryWithObjectsAndKeys", but why it isn't done as "dictionaryWithKeysAndObjects" I have no idea.