What is the real advantage of using a CallBack?

Arungiri G

5y1.1kVisual Basic .NET

What is the real advantage of using a CallBack explain with code please

8 Replies

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Rajanikant Hawaldar5y ago
Accepted answer
The advantage is that you can define a parameter in a class that is actually a function. This exempts the programmer from a framework, for example, from writing this function, leaving it to a programmer. The framework only calls the function defined by the programmer without necessarily checking what this function does.

In simple terms:

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

A callback is a function that will be called when a process is done executing a specific task. The usage of a callback is usually in asynchronous logic. To create a callback in C#, you need to store a function address inside a variable. This is achieved using a delegate or the new lambda semantic Func or Action.
public delegate void WorkCompletedCallBack(string result);



    public void DoWork(WorkCompletedCallBack callback)

    {

        callback("Hello world");

    }



    public void Test()

    {

        WorkCompletedCallBack callback = TestCallBack; // Notice that I am referencing a method without its parameter

        DoWork(callback);

    }



    public void TestCallBack(string result)

    {

        Console.WriteLine(result);

    }

In today C#, this could be done using lambda like:
public void DoWork(Action<string> callback)

{

callback("Hello world");

}



public void Test()

{

DoWork((result) => Console.WriteLine(result));

}
Mageshwaran R5y ago
Hi Arungiri,
please refer this link,
https://www.c-sharpcorner.com/UploadFile/1c8574/delegate-used-for-callback-operation/
Kiran Mohanty5y ago
In case of asynchronous programming, when we wish to do some operation after async call completion, we need callback functions.
Ex-
function f1(){
  $.ajax({
      // your code
   });
   callAfterAjax();
}
Here callAfterAjax() will not wait for ajax completion . But if we write it as
function f1(){
  $.ajax({
      // your code
     success: function (){
            callAfterAjax();
     }
   });
}
Here application will execute callAfterAjax() once ajax call is done.
Note :- success is jquery framework defined callback function.
Sachin Singh5y ago
Okk then you are talking about delegate i think and its callback
The one and the only purpose of delegate Callback in your context is to decouple your Method from logic. You can paas method as parameter of a method.
What is meant by decopling a Method from Logic?
suppose there is an Employee class and it has a method PromoteEmployee.
Employee can be promoted by thier age if age<20 say Or
Employee can be promoted by their salary if salary< 25K say
Suppose you don't know at present moment of time , which of the above critaria the callee of the method wants,
some times he wants the method to return all employees based on their age and sometimes he wants to return all employees based on Salary, completely on his mood.
As a developer how will you implement a method whose Logic is not fixed???
Here comes delegate.
public  class Employee
  {
    public delegate bool isPromotable(Employee emp); // delegate

      public string Name { get; set; }
      public int Age { get; set; }
      public int Salary { get; set; }
      public IEnumerable PromoteEmployee(List employees,isPromotable IsEligible)
      {
          foreach(Employee emp in employees){
              if (IsEligible(emp))
              {
                yield  return emp.Name +" "+ "promoted";
              }
          }
      }
  }
Now the method is decoupled from the Logic and he who will call it will be responsible for providing the logic as we have used delegate he can implement a method of same signature or can pass a lambda expression (short version of creating method)
           List employeess = new List(){
               new Employee(){Name="Ram",Age=18,Salary=21000},
                new Employee(){Name="shyam",Age=21,Salary=2000},
                 new Employee(){Name="Govind",Age=51,Salary=26000},
                  new Employee(){Name="Khurana",Age=41,Salary=29000},
                   new Employee(){Name="Madhukar",Age=30,Salary=61000},
           };
           foreach (string str in emp.PromoteEmployee(employeess, e1 => e1.Age < 20))
           {
               Console.WriteLine(str);
           }


Or he can give other logic for promotion based on Salary like
foreach (string str in emp.PromoteEmployee(employeess, e1 => e1.Salary < 25000))
           {
               Console.WriteLine(str);
           }
Rajanikant Hawaldar5y ago
Yes it is
Arungiri G5y ago
is callback in other languages also?
Arungiri G5y ago
C#
Sachin Singh5y ago
In which context you are asking about callback? which language ?