What is the need of delegate than calling the normal function via object of the class ?

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lets' say I have 2 buttons. Add & Substract.
I will write two seperate functions "Add" & "Substract" & i will call them accordingly on each button click.
Then why should I go for delegate when things are already known to me in advance which function to call on which button click ?

What I have tried:

I have tried implementing it via both normal function calling & also by implementing via delegate.
But i did not get the difference when to use delegate over normal function call.

Posted 2-Apr-16 5:18am

Member 9346617

Updated 2-Apr-16 10:45am

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OriginalGriff · Answer 1 · 2016-04-02T05:37:00

Delegates are used for more than just "call this or that" - they can provide a "chain of methods to be called" for example. You use delegates already, quite a bit - you just don't realize it because they are "hidden" at the core of Event handling!

One reason for a delegate based approach is it's flexibility: you don;t have to write code which "works out" which method to call:

C#

private DoIt(MyEnum functionType)
   {
   switch(functionType)
      {
      case MyEnum.Add: Add(); break;
      case MyEnum.Sub: Sub(); break;
      default: throw new ParameterException("Unknown function type: " + functionType);
      }
   }

C#

private DoIt(MyDelegate del)
   {
   if (del != null)
      {
      del();
      }
   }

When you add Mult and Div methods, you don't have to change the code in DoIt at all - you just pass the appropriate delegate and it all works transparently.

One example of this is a Sort method, when you pass a comparison delegate to compare UserNames, or a different delegate to compare BirthDates depending on what you want to sort - provided the methods match the delegate signature and return the right value (-1, 0, or +1) the sort will work without caring what it it actually comparing!

Sergey Alexandrovich Kryukov · Answer 2 · 2016-04-02T10:45:00

Your logic is badly, badly flawed. You start from the point where there should not be any essential difference by definition, and then, based on that, draw a conclusion that there is no difference.

If you still did not get it, I'll explained on another example. This is like considering a microscope as a device for hammering in nails, but with a number of part of unknown purpose. This is your starting point in first place. Then you take it, hammer a nail, and conclude that if functions the same way as the hummer, and the unknown parts are not utilized in the process, so a question should be raised, "aren't they useless?"… This is exactly what you have done.

Actually, the delegate is one of the implementations of a very deep conception: methods as first-class objects. A delegate is an object, and unlike a method, its instance can be passed as a method argument or the type member reference, a property or a field. This way, this is another device of abstraction, along with, say, method parameter-passing or variable. This is how it explained in Wikipedia:
https://en.wikipedia.org/wiki/Delegation_%28programming%29[^],
First-class citizen — Wikipedia, the free encyclopedia[^].

I cannot blame you much in not understanding .NET delegates, specifically. Not many developers understand their full capacity. Unfortunately, this is because MSDN documentation, comprehensive in most parts, leave a lot of mystery about delegates and delegate instances; its help pages on the topic are closer to some cook-book recipes and leave important functionality, forget the mechanism, behind the scene.
Big part of it is described in one section of my article: Dynamic Method Dispather, 4.1. On the Nature of Delegate Instance.

—SA

What is the need of delegate than calling the normal function via object of the class ?

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