JSONRepresentation for NSMutableDictionary

I want to call the JSONRepresentation method on an NSMutableDictionary object. I'm calling it using [userDict JSONRepresentation];, but I am getting the following warning:

NSMutableDictionary may not responsd to '-JSONRepresentation'

Could anyone tell me how to I can properly call the JSONRepresentation method on an object 开发者_如何学编程of the NSMutableDictionary type?

Thanks in advance.

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The JSONRepresentation method comes from json-framework. Include that framework in your project and import the correct headers, and you should be good to go.