IOS/Objective-C: Convert NSArray of Custom Objects to JSON

Question

Based on the accepted answer to this answer, I am trying to send an array of custom objects via JSON to a server.

However, the following code to serialize the objects is crashing. I think it because NSJSONSerialization can only accept an NSDictionary, not a custom object.

NSArray <Offers *> *offers = [self getOffers:self.customer];
//Returns a valid array of offers as far as I can tell.
NSError *error;
//Following line crashes
NSData * JSONData = [NSJSONSerialization dataWithJSONObject:offers
                                                    options:kNilOptions
                                                      error:&error];

Can anyone suggest way to convert an array of custom objects to JSON?

Possible duplicate of serialize objective-c custom object to JSON for OSX? and Serialize and Deserialize Objective-C objects into JSON — rmaddy
– rmaddy, Commented Jul 7, 2018 at 15:38

Gereon · Accepted Answer · 2018-07-09 11:41:07Z

2

Like you said, NSJSONSerialization only understands Dictionaries and Arrays. You'll have to provide a method in your custom class that converts its properties into a Dictionary, something like this:

@interface Offers 
@property NSString* title;
-(NSDictionary*) toJSON;
@end

@implementation Offers
-(NSDictionary*) toJSON {
    return @{
       @"title": self.title
    };
}
@end

then you can change your code to

NSArray <Offers *> *offers = [self getOffers:self.customer];
NSMutableArray<NSDictionary*> *jsonOffers = [NSMutableArray array];
for (Offers* offer in offers) {
    [jsonOffers addObject:[offer toJSON]];
}
NSError *error;
//Following line crashes
NSData * JSONData = [NSJSONSerialization dataWithJSONObject:jsonOffers
                                                    options:kNilOptions
                                                      error:&error];

edited Jul 9, 2018 at 11:41

answered Jul 7, 2018 at 15:30

Gereon

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1 Comment

user6631314 Over a year ago

Hi, I have discovered that the method toJSON in the custom class (NSManagedObject) is returning empty values. If a property in offers is @property (nonatomic, retain) NSString * title; what would the correct code be to get the title through [offer toJSON]?

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