How to convert class object to json string in objective c

Question

1.I create class objects then add value to my class with this code

csJastorPollQuestion *pq = [[csJastorPollQuestion alloc] initWithID:@"01" Name:@"AAA"];

2.I shown "csJastorPollQuestion" in NSLog it's present

#<csJastorPollQuestion: id = (null) { ID = 01; Name = AAA; }>

3.I convert "csJastorPollQuestion" to json string with this code

NSData *jsd = [NSJSONSerialization dataWithJSONObject:pq options:NSJSONWritingPrettyPrinted error:&er];
NSString *jsonString = [[NSString alloc] initWithData:jsd encoding:NSUTF8StringEncoding];

4.When I run my project it's shown error this

[NSJSONSerialization dataWithJSONObject:options:error:]: Invalid top-level type in JSON write'

5.What is the right way for convert "csJastorPollQuestion" to json string?

Stick it in a dictionary. JSON requires the top level object be either a dictionary or an array. — CodaFi
– CodaFi, Commented Feb 12, 2014 at 3:40

jiwq · Accepted Answer · 2016-11-01 07:52:50Z

I think you should reflect your own object to NSDictionary and used NSJSONSerialization convert to JSON string.

Reflect from attributes:

    - (NSDictionary *)dictionaryReflectFromAttributes
    {
        @autoreleasepool
        {
            NSMutableDictionary *dict = [NSMutableDictionary dictionary];
            unsigned int count = 0;
            objc_property_t *attributes = class_copyPropertyList([self class], &count);
            objc_property_t property;
            NSString *key, *value;

            for (int i = 0; i < count; i++)
            {
                property = attributes[i];
                key = [NSString stringWithUTF8String:property_getName(property)];
                value = [self valueForKey:key];
                [dict setObject:(value ? value : @"") forKey:key];
            }

            free(attributes);
            attributes = nil;

            return dict;
        }
    }

Convert to JSON string:

    - (NSString *)JSONString
    {
        NSDictionary *dict = [self dictionaryReflectFromAttributes];
        NSError *error;
        NSData *jsonData = [NSJSONSerialization dataWithJSONObject:dict options:NSJSONWritingPrettyPrinted error:&error];
        if (jsonData.length > 0 && !error)
        {
             NSString *jsonString = [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];
             return jsonString;
        }
        return nil;
    }

Tom Harrington · Accepted Answer · 2014-02-12 03:55:16Z

1

The dataWithJSONObject:options:error: method only works on objects that NSJSONSerialization knows how to convert to JSON. That means:

The top-level object must be an NSArray or NSDictionary
Objects contained must be instances of NSString, NSNumber, NSArray, NSDictionary, or NSNull.
Dictionary keys must be NSStrings
Numbers must not be infinite or NaN.

You need to convert to a dictionary or array representation to use this method.

answered Feb 12, 2014 at 3:55

Tom Harrington

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