Delegates are a type that indirectly calls a method using a pointer.
This console application implements a multicast delegate called multiCastDel that combines four methods: Add(), Subtract(), Divide() and Multiply().
using System;
namespace Test
{
delegate void CalculateDel(double a, double b);
class Program
{
public static void Add(double first, double second)
{
double sum = first + second;
Console.WriteLine("The sum of {0} and {1} is {2}.", first, second, sum);
}
public static void Subtract(double first, double second)
{
double difference = first - second;
Console.WriteLine("The difference of {0} and {1} is {2}.", first, second, difference);
}
public static void Multiply(double first, double second)
{
double multiplier = first * second;
Console.WriteLine("If you multiply {0} by {1}, the result is {2}.", first, second, multiplier);
}
public static void Divide(double first, double second)
{
double quotient = first / second;
if (double.IsInfinity(quotient))
{
Console.WriteLine("Division by zero is not possible. Please enter a divisor value that is not zero.");
}
else
{
Console.WriteLine("If you divide {0} by {1}, the result is {2}.", first, second, quotient);
}
}
static void Main(string[] args)
{
CalculateDel addDel;
CalculateDel subDel;
CalculateDel mulDel;
CalculateDel divDel;
addDel = new CalculateDel(Add);
subDel = new CalculateDel(Subtract);
mulDel = new CalculateDel(Multiply);
divDel = new CalculateDel(Divide);
CalculateDel multiCastDel;
multiCastDel = addDel + subDel + mulDel + divDel;
double prompt = 0;
do
{
Console.WriteLine("Please enter the first double number or -1 to discontinue:");
prompt = Convert.ToDouble(Console.ReadLine());
if (prompt == -1)
{
Console.WriteLine("You have decided to quit the Centennial College Multicast Delegate Application.");
Console.WriteLine("Good-bye.");
break;
}
else
{
double firstInput = prompt;
Console.WriteLine("Please enter the second double number:");
double secondInput = Convert.ToDouble(Console.ReadLine());
multiCastDel(firstInput, secondInput);
}
} while (prompt != -1);
Console.ReadKey();
}
}
}
CalculateDel is a global delegate type which represents all void methods that take two double variables as parameters. The four methods (Add, Subtract, Divide and Multiply) have the same signature as the CalculateDel delegate declared in the beginning.
The multiCastDel delegate is an object of CalculateDel which will output results of all four methods at once.
Test output screenshot:
So, you're probably wondering, "Why do I need to indirectly call methods in the first place?" You didn't really need to actually multicast these four methods with delegates to get the same result.
The point of delegates is to allow easy communication between parties. When you define a delegate, you are essentially allowing any method that matches the signature of the delegate to be called. It would also be a great way of testing methods that you created with the same parameters.
Conclusion
Delegates reference methods with a specific set of parameters and return type. They are object-oriented, they can be passed as parameters and they can even be bundled together into a single event.