This section describes using the method callback interfaces of this toolkit which includes the wwMethodCallback server control which makes it real easy to create code that calls class methods in server side code and return the results back to the client as JSON.

A number of mechanisms are available for calling server methods from the client:

• AjaxMethodCallback server control
  
• AjaxMethodCallback client class
  
• ServiceProxy class to call WCF Services
  
• Raw AJAX callbacks using any AJAX library
  

On the server you can choose to implement callback methods in:

• HttpHandler deriving from CallbackHandler with [CallbackMethod] Attributes
  (best performance and recommended approach)
  
• Page Methods using [CallbackMethod] Attributes
  
• In custom and user controls using [CallbackMethod] Attributes
  

The following topics are discussed here:

• Basic Page Callbacks using AjaxMethodCallback
• Passing Complex Objects in Callbacks
• Implementing Callback Methods on Custom or User Controls
• Using a CallbackHandler HttpHandler for optimized Callbacks
• Using CallbackHandler with GET Requests
• Returning non-JSON Data from Callback Methods
• Using CallbackHandler with REST Calls
• Calling WCF and ASMX Services with AjaxMethodCallback
• JSONP Callback Support