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Delegate in c# with simple example

Delegate in C#   
Delegate is an object which holds the references to a method within delegate object. 
Delegate is a type-safe object.
Delegate is invoke to methods in asynchronously manner.
Delegate encapsulates a static methods or instance methods instance.
Delegate can be with parameters or without parameters.    
Most importent use of delegate:    
1. Improve the performance of application.
2. Encapsulat to methods call from caller.
3. Call a method asynchronously.   
Three steps for using delegates:  
    1. Declare
    2. Create
    3. Point   
Delegate are Two types:    
1. Delegate
2. Multicast Delegate  
Generic readymade delegate are :     
1. Func< input, output >
2. Action< inputParameter >
3. Predicate< inputParameter >   
Delegate is use when we needed to pass the single reference to a method within delegate object.
Multicast Delegate is use when we needed to pass the nore then one reference to a method within delegate object.
Declaration of Delegate:   public delegate delegate_type delegate_name();
Delegate Example  
namespace delegateExample
{
    public delegate int AddByDelegate(int var1, int var2);
    public class DelegateClass
    {
        public static int Add(int a, int b)
        {
            return a + b;
        }
        static void Main(string[] args)
        {
            //Creating the Delegate Instance
            AddByDelegate delObject = new AddByDelegate(Add);
            Console.Write("Please enter value");
            int num1 = Int32.Parse(Console.ReadLine());
            int num2 = Int32.Parse(Console.ReadLine());
            // Here method Add is call.
            int Result = delObject(num1, num2);
            Console.WriteLine("Result:" + Result);
            Console.ReadLine();
        }
    }
}
OutPut: Result : 30
Example for mapped to both static and instance methods
namespace Delegates
{
    delegate void MyDelegate();
    public class MyClass
    {
        public void InstanceMethods()
        {
            Console.WriteLine("Instance method call");
        }
        static public void StaticMethods()
        {
            Console.WriteLine("Static method call");
        }
    }
    public class MyMainClass
    {
        static public void Main()
        {
            MyClass MCObj = new MyClass();
            // Delegate Map to the instance method
            MyDelegate myDelInstObj = new MyDelegate(MCObj.InstanceMethods);
            myDelInstObj();
            //Delegate Map to the static method:
            myDelInstObj = new MyDelegate(MyClass.StaticMethods);
            myDelInstObj();
            Console.Read();
        }
    }
}  
Multicast Delegate     
Multicast delegate is hold the references of more than one method within delegate object using the += operator.

    Delegate is added using the += operator.
    Delegate is removed using the -= operator.    
Example for Multicast Delegate  
namespace MulticastDelegateExample
{
    public delegate int MulticastDelegateName(int num1, int num2);
    public class MulticastClass
    {
        public static int Add(int num1, int num2)
        {
            return num1 + num2;
        }
        public static int Sub(int num1, int num2)
        {
            return num1 - num2;
        }
        static void Main(string[] args)
        {
            //Create the Add Delegate Instance
            MulticastDelegateName objDelegt = new MulticastDelegateName(Add);
            Console.WriteLine("Please enter numbers!");
            int num1 = Int32.Parse(Console.ReadLine());
            int num2 = Int32.Parse(Console.ReadLine());
            int AddRest = objDelegt(num1, num2);
            Console.WriteLine("Result :" + AddRest);
            //Create the Sub Delegate Instance
            objDelegt += new MulticastDelegateName(Sub);
            int subRest = objDelegt(num1, num2);
            Console.WriteLine("Result :" + subRest);
            Console.ReadLine();
        }
    }
}
OutPut: Please enter numbers! num1 = 20 num2 = 10 Results: Add: 30 and Sub: 10
Generics Delegate    
Microsoft provides three readymade generics delegate. 
This is call shorter and sweeter delegate using this to minimise the code complexity. 
    
1. Func< input, output >
2. Action< inputParameter >
3. Predicate< inputParameter >    
Func< input, output >
Func generics delegate is use, when we have need to some input parameter and then return some output.
namespace GenericDelegate
{
   public class Delegates
    {
        static void Main(string[] args)
        {
            // int is a input parameter and double is output parameter
            Func<int, double> calPiR2Obj = r => 3.12 * r * r;
            Console.Write(calPiR2Obj(4));
            Console.ReadLine();
        }
    }
}
Action< inputParameter >    
Action generics delegate is use, when we have need to input parameter and no need to 
return output that means return void.

Example:  
namespace GenericDelegate
{
    public class Delegates
    {
        static void Main(string[] args)
        {
            Action<string> ActionObject = x => Console.WriteLine(x);
            ActionObject("This is Action delegate!");
            Console.ReadLine();
        }
    }
}
Predicate< inputParameter >  
Predicate generics delegate is use, when we have need to input parameter and return output is 
Boolean type just like true or false.

This delegate is uses when we need to check the condition result is true or false.
Example

namespace GenericDelegate
{
    public class Delegates
    {
        static void Main(string[] args)
        {
            //string is input but out put is retun True or False
            Predicate<string> checkConditionIsTF = x => x.Length > 10;           
Console.WriteLine(checkConditionIsTF("Anil Kumar Singh"));
            Console.ReadLine();
        }
    }
}
Generic Delegate Example     
namespace GenericDelegate
{
    public class Delegates
    {
        static void Main(string[] args)
        {
            // int is a input parameter and double is output parameter.
            Func<int, double> calPiR2Obj = r => 3.12 * r * r;
            Console.WriteLine(calPiR2Obj(4));
            //string is input but no output return.
            Action<string> ActionObject = x => Console.WriteLine(x);
            ActionObject("This is Action delegate!");
            //string is input but out put is retun True or False
            Predicate<string> checkConditionIsTF = x => x.Length > 10;           
Console.WriteLine(checkConditionIsTF("Anil Kumar Singh"));
            Console.ReadLine();
        }
    }
}
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