What is a callback function delegate?

Question

Anyone please explain with example what is callback function delegate ? when to use ?... Thanks in Advance

Rajeesh Menoth · Answer

Hi Karthikeyan, Answer for Charles Bretana : A "callback" is a term that refers to a coding design pattern, available in any language that has function pointers, or an analogue to function pointers (which is kinda what a delegate is) In this pattern, you pass a pointer to a function to another function, so that within the called function, it can "call back" the function you passed to it. In this way you can control a large chunk of the internal behavior of a method from outside the method, by passing pointers to different "callback" function each time you call it... An example of a callback is when you have a sorting algorithm that has to be passed a pointer to a function that will "compare" any arbitrary pair of objects in the list to be sorted, to determine which goes before the other. On one call to the sort method, you might pass a callback function that compares by object name, and another time pass a function that compares by object weight, or whatever... A Delegate, otoh, is a specific .Net type that acts as a signature-specific container for a function pointer... In .Net managed code, delegates are the only way to create and use a function pointer. So in .Net to do a callback, you are in fact passing a delegate... But delegates can be used in other scenarios besides callbacks. (specifically, delegates can be also used to implement multi-threading from the .Net thread pool) Refer the following article then you will get more idea about Callback function in delegate. Reference : http://www.codeproject.com/Articles/426120/Calling-a-method-in-Csharp-asynchronously-using-de http://zetcode.com/lang/csharp/delegates/ http://stackoverflow.com/questions/290819/are-delegates-and-callbacks-the-same-or-similar

Vinay Singh · Answer

A callback is basically a delegate passed into a procedure which that procedure will " call back " at some appropriate point. For example, in asynchronous calls such as WebRequest.BeginGetResponse or a WCF BeginXxx operation, you'd pass an AsyncCallback

Joginder Banger · Answer

Hello Dear, A callback is basically a delegate passed into a procedure which that procedure will "call back" at some appropriate point. For example, in asynchronous calls such as WebRequest.BeginGetResponse or a WCF BeginXxx operation, you'd pass an AsyncCallback. The worker will "call back" whatever method you pass in as the AsyncCallback, in this case when it's finished to let you know that it's finished and to obtain the result. An event handler could be considered another example. For example, when you attach a handler to a Click event, the button will "call back" to that handler when the click occurs Source : Statckoverflow.com

What is a callback function delegate?

Answers (3)