Objective-C types are mapped to JSON types in the following way:

• NSNull -> null
• NSString -> string
• NSArray -> array
• NSDictionary -> object
• NSNumber's -initWithBool:YES -> true
• NSNumber's -initWithBool:NO -> false
• NSNumber -> number

覚え書き

In JSON the keys of an object must be strings. NSDictionary keys need not be, but attempting to convert an NSDictionary with non-string keys into JSON will throw an exception.

NSNumber instances created with the -numberWithBool: method are converted into the JSON boolean "true" and "false" values, and vice versa. Any other NSNumber instances are converted to a JSON number the way you would expect.