What is a callback?

Question

What\'s a callback and how is it implemented in C#?

Answer 1

Probably not the dictionary definition, but a callback usually refers to a function, which is external to a particular object, being stored and then called upon a specific event.

An example might be when a UI button is created, it stores a reference to a function which performs an action. The action is handled by a different part of the code but when the button is pressed, the callback is called and this invokes the action to perform.

C#, rather than use the term 'callback' uses 'events' and 'delegates' and you can find out more about delegates here.

Answer 2

callback work steps:

1) we have to implement ICallbackEventHandler Interface

2) Register the client script :

 String cbReference = Page.ClientScript.GetCallbackEventReference(this, "arg", "ReceiveServerData", "context");
    String callbackScript = "function UseCallBack(arg, context)" + "{ " + cbReference + ";}";
    Page.ClientScript.RegisterClientScriptBlock(this.GetType(), "UseCallBack", callbackScript, true);

1) from UI call Onclient click call javascript function for EX:- builpopup(p1,p2,p3...)

var finalfield= p1,p2,p3; UseCallBack(finalfield, ""); data from the client passed to server side by using UseCallBack

2) public void RaiseCallbackEvent(string eventArgument) In eventArgument we get the passed data //do some server side operation and passed to "callbackResult"

3) GetCallbackResult() // using this method data will be passed to client(ReceiveServerData() function) side

callbackResult

4) Get the data at client side: ReceiveServerData(text) , in text server response , we wil get.

Answer 3

A callback is a function pointer that you pass in to another function. The function you are calling will 'callback' (execute) the other function when it has completed.

Check out this link.

Answer 4

A callback lets you pass executable code as an argument to other code. In C and C++ this is implemented as a function pointer. In .NET you would use a delegate to manage function pointers.

A few uses include error signaling and controlling whether a function acts or not.

Wikipedia

Answer 5

In computer programming, a callback is executable code that is passed as an argument to other code.

—Wikipedia: Callback (computer science)

C# has delegates for that purpose. They are heavily used with events, as an event can automatically invoke a number of attached delegates (event handlers).

Answer 6

I just met you,
And this is crazy,
But here's my number (delegate),
So if something happens (event),
Call me, maybe (callback)?