How to Pass a Function as a Parameter in C#

1. Pass a Function as a Parameter With the Func<> Delegate in C#
2. Pass a Function as a Parameter Inside Another Function With the Action<> Delegate in C#

This tutorial will introduce methods to pass a function as a parameter inside another function in C#.

Pass a Function as a Parameter With the Func<> Delegate in C#

The Func<T1, T-return> delegate defines a function with T1 parameter and T-return return type in C#. We can pass a function as a parameter inside another function with the Func<T1, t-return> delegate. The following code example shows us how we can pass a function as a parameter inside another function with the Func<> delegate in C#.

using System;

namespace pass_function_as_parameter {
  class Program {
    static int functionToPass(int x) {
      return x + 10;
    }
    static void function(Func<int, int> functionToPass) {
      int i = functionToPass(22);
      Console.WriteLine("i = {0}", i);
    }
    static void Main(string[] args) {
      function(functionToPass);
    }
  }
}

Output:

i = 32

We defined the function functionToPass(int x) which takes an integer value as a parameter, increments it with 10 and returns the result as an integer value. We passed the functionToPass() function as a parameter to the function() function with the Func<int, int> delegate. We passed the value 22 to the functionToPass() function inside the function() function. In the main function, we called the function with function(functionToPass) function call. The Func<> delegate can only be used to pass the functions that return some value.

Pass a Function as a Parameter Inside Another Function With the Action<> Delegate in C#

If we want to pass a function that does not return a value, we have to use the Action<> delegate in C#. The Action<T> delegate works just like the function delegate; it is used to define a function with the T parameter. We can use the Action<> delegate to pass a function as a parameter to another function. The following code example shows us how we can pass a function as a parameter inside another function with the Action<> delegate in C#.

using System;

namespace pass_function_as_parameter {
  class Program {
    static void functionToPass2(int x) {
      int increment = x + 10;
      Console.WriteLine("increment = {0}", increment);
    }
    static void function2(Action<int> functionToPass2) {
      functionToPass2(22);
    }
    static void Main(string[] args) {
      function2(functionToPass2);
    }
  }
}

Output:

increment = 32

We defined the function functionToPass2(int x) which takes an integer value as a parameter, increments it with 10 and prints the result. We passed the functionToPass2() function as a parameter to the function() function with the Action<int> delegate. We passed the value 22 to the functionToPass2() function inside the function2() function. In the main function, we called the function with function2(functionToPass2) function call. The Action<> delegate can only be used to pass the functions that do not return any value.