Convert between JSON String and NSDictionary/NSArray

Objective C Apr 17, 2020 Viewed 933 Comments 0

In iOS, the NSJSONSerialization class of Objective C is used to convert between JSON strings and objects, such as NSDictionary and NSArray , etc.

Convert NSDictionary/NSArray to JSON

Use dataWithJSONObject:options:error: method.

There are 4 values for NSJSONWritingOptions.

1. NSJSONWritingPrettyPrinted

The writing option that uses white space and indentation to make the output more readable.

2. NSJSONWritingSortedKeys

The writing option that sorts keys in lexicographic order.

3. NSJSONWritingFragmentsAllowed

4. NSJSONWritingWithoutEscapingSlashes

// NSDictionary
NSDictionary *dictionaryOrArray = @{@"value": @"blue", @"key": @"color"};
// NSArray
// NSArray *dictionaryOrArray = @[@"color", @"blue"];
NSError *error;
NSData *jsonData = [NSJSONSerialization dataWithJSONObject:dictionaryOrArray
                                                   options:NSJSONWritingPrettyPrinted
                                                     error:&error];

if (error) {
    NSLog(@"Got an error: %@", error);
} else {
    NSString *jsonString = [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];
    NSLog(@"%@", jsonString);
}

Convert JSON String to NSDictionary/NSArray

Use JSONObjectWithData:options:error: function.

There are 4 values for NSJSONReadingOptions.

1. NSJSONReadingMutableContainers

Specifies that arrays and dictionaries are created as mutable objects.

2. NSJSONReadingMutableLeaves

Specifies that leaf strings in the JSON object graph are created as instances of NSMutableString.

3. NSJSONReadingAllowFragments

Specifies that the parser should allow top-level objects that are not an instance of NSArray or NSDictionary.

4. NSJSONReadingFragmentsAllowed

NSJSONReadingAllowFragments and NSJSONReadingFragmentsAllowed , which can convert @"32"  to NSNumber 32, or convert @"\"32\"" to NSString @"32" .

NSString *jsonString = @"{ \"colors\": [ \"red\", \"green\" ] }";
NSData *jsonData = [jsonString dataUsingEncoding:NSUTF8StringEncoding];
NSError *error;
NSMutableDictionary *data = [NSJSONSerialization JSONObjectWithData:jsonData
                                                   options:NSJSONReadingAllowFragments
                                                     error:&error];

if (error) {
    NSLog(@"Got an error: %@", error);
} else {
    NSLog(@"%@", data);
}
Updated Apr 17, 2020