ios - Keeping the order of NSDictionary keys when converted to NSData with [NSJSONSerialization dataWithJSONObject:]

Question

I have the following situation:

NSDictionary *params = @{
    @"Checkout" : @{
        @"conditions" : @{@"Checkout.user_id" : @1},
        @"order" : @{@"Checkout.id" : @"DESC"}
    },
    @"PaymentState" : @[],
    @"Offer" : @[]
};

This dictionary contains params for a webservice request passing a JSON string with the webservice URL. I get the JSON string using NSJSONSerialization class, like this:

NSData *jsonData = [NSJSONSerialization dataWithJSONObject:params options:0 error:nil];
NSString *jsonString = [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];

The problem is: jsonString "keys" is ordered differently from the original params dictionary keys order, like this:

{
"Offer":[],
"PaymentState":[],
"Checkout":{
    "conditions":{"Checkout.user_id":6},
    "order":{"Checkout.id":"DESC"}
}

}

That is, the "PaymentState" and "Offer" keys come first in jsonString, and i need maintain the original order. This is very important, like this:

{
"Checkout":{
    "conditions":{"Checkout.user_id":6},
    "order":{"Checkout.id":"DESC"}
},
"Offer":[],
"PaymentState":[]

}

So guys, how can i do that??

Answer 1

I use OrderedDictionary from CocoaWithLove whenever I need to keep the order of my dictionary keys.

Basically, OrderedDictionary contains an NSMutableDictionary and an NSMutableArray for the keys inside it, to keep track of the order of the keys. It implements the required methods for subclassing NSDictionary/NSMutableDictionary and just "passes" the method call to the internal NSMutableDictionary.