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