C# Language Delegates Combine Delegates (Multicast Delegates)
Example
Addition + and subtraction - operations can be used to combine delegate instances. The delegate contains a list of the assigned delegates.
using System;
using System.Reflection;
using System.Reflection.Emit;
namespace DelegatesExample {
class MainClass {
private delegate void MyDelegate(int a);
private static void PrintInt(int a) {
Console.WriteLine(a);
}
private static void PrintType<T>(T a) {
Console.WriteLine(a.GetType());
}
public static void Main (string[] args)
{
MyDelegate d1 = PrintInt;
MyDelegate d2 = PrintType;
// Output:
// 1
d1(1);
// Output:
// System.Int32
d2(1);
MyDelegate d3 = d1 + d2;
// Output:
// 1
// System.Int32
d3(1);
MyDelegate d4 = d3 - d2;
// Output:
// 1
d4(1);
// Output:
// True
Console.WriteLine(d1 == d4);
}
}
}
In this example d3 is a combination of d1 and d2 delegates, so when called the program outputs both 1 and System.Int32 strings.
Combining delegates with non void return types:
If a multicast delegate has a nonvoid return type, the caller receives the return value
from the last method to be invoked. The preceding methods are still called, but their
return values are discarded.
class Program
{
public delegate int Transformer(int x);
static void Main(string[] args)
{
Transformer t = Square;
t += Cube;
Console.WriteLine(t(2)); // O/P 8
}
static int Square(int x) { return x * x; }
static int Cube(int x) { return x*x*x; }
}
t(2) will call first Square and then Cube. The return value of Square is discarded and return value of the last method i.e. Cube is retained.
