如何在wpf应用程序中使用json响应

Question

My wpf application is communicating with php web api. First I post some data to web api and recieved json resonse. At server side php script just prepared an array and json_encode(arrayName)is sent to client. At my client side I am using following code

using (WebResponse jsonResponse = request.GetResponse())
            {
                // Do something with response
                StreamReader streamReader = new StreamReader(jsonResponse.GetResponseStream());
                String responseData = streamReader.ReadToEnd();

                MessageBox.Show(responseData);
            }

in the message box I am able to see all the data sent by server. Now I don't have any idea how to assign this data to local variables? Kindly guide me.

http://i.imgur.com/1Qzds8G.png

EDIT

Response shown in message box is :-

[{"response":"true","user_id":"250","username":"sapan108"}]'

After Googling I created following class :-

public class UserData
{
    public string response { get; set; }
    public string error { get; set; }
    public int user_id { get; set; }
    public string username { get; set; }
}

Now How to assign json response to these variables.

Note: Due to less reputation unable to post image directly. Sorry for inconvenience.