Building NSMutableArray from NSMutableDictionary resulting in NSException - ios

Question

I am a newbie in iOS development. I was trying to put the results of an NSMutableArray into an NSMutableString but this is resulting in an NSException.
Here is my code:
NSMutableArray *oldtableData = .......this is where I recieve card data;
NSError *error;
NSMutableData *tableDataUpdated = [[NSJSONSerialization dataWithJSONObject:oldtableData
options:0
error:&error] copy];
NSMutableDictionary *cardDictionary = [NSJSONSerialization JSONObjectWithData:tableDataUpdated options:0 error:NULL];
For converting the cardDictionary into a NSMutableArray, I am using this piece of code (which is giving me an NSException)
NSMutableArray *type = [NSMutableArray array];
NSMutableArray *last4Digits = [NSMutableArray array];
[cardDictionary enumerateKeysAndObjectsUsingBlock:^(id key, id obj, BOOL *stop) {
[type addObject:[obj valueForKeyPath:#"type"]];
[last4Digits addObject:[obj valueForKeyPath:#"last4Digits"]];
}];
But If I exclude the above code and try NSLog with this piece of code
NSLog(#"JSON: %#",cardDictionary);
Console will give a proper json result; something like this:
JSON: (
{
cardPciId = "###########";
fingerPrint = ###########;
last4Digits = 4321;
type = Mastercard;
},
{
cardPciId = "###########";
fingerPrint = ###########;
last4Digits = 1234;
type = Visa;
}
)
I am trying to convert this into two Arrays, one with all the "type"s and another one with all "last4Digits". But this is what I get
Uncaught exception: -[__NSCFArray enumerateKeysAndObjectsUsingBlock:]:
unrecognized selector sent to instance 0x7ff7060badf0
I tried to hover through StackOverFlow to find a solution but none of them seem to be working. :(

Answer 1

It looks like cardDictionary is actually an NSArray instance containing the dictionaries. So, you should iterate through the array, and get type and last4Digits from each dictionary using objectForKey instead of valueForKeyPath:
NSArray *cardDictionaries = [NSJSONSerialization JSONObjectWithData:tableDataUpdated options:0 error:NULL];
NSMutableArray *type = [NSMutableArray array];
NSMutableArray *last4Digits = [NSMutableArray array];
[cardDictionaries enumerateObjectsUsingBlock:^(NSDictionary *cardDictionary, NSUInteger idx, BOOL *stop) {
[type addObject:[cardDictionary objectForKey:#"type"]];
[last4Digits addObject:[cardDictionary objectForKey:#"last4Digits"]];
}];

Answer 2

There is a lot going on here, but I want to point one thing out.
Table data is being serialized to JSON.
NSMutableData *tableDataUpdated = [[NSJSONSerialization dataWithJSONObject:oldtableData
options:0
error:&error] copy];
Next, the data that was just serialized is de-serialized. It will always be the same array.
NSMutableDictionary *cardDictionary = [NSJSONSerialization JSONObjectWithData:tableDataUpdated options:0 error:NULL];
You will always get the same data back. You don't need to do the JSON step at all.