Write an OnReceivingData event handler to provide the end-user with feedback of the progress when receiving a request that contains a large amount of data. When the content of a response is very large (for example, when it contains large attachments), it is broken into blocks, which are sent separately. After receiving each of these blocks, the Receive method generates an OnReceivingData event. You can use the event handler to update a progress bar or similar control to indicate how much of the response has been received. 

OnPostingData 

Receive