C# 4 and .NET 4

194 ❘ ChaPTer 8 deleGAtes, lAmbdAs, And events
To illustrate the use of multicast delegates, the following code recasts the SimpleDelegate example into
a new example, MulticastDelegate. Because you now need the delegate to refer to methods that return
void, you have to rewrite the methods in the MathOperations class, so they display their results instead of
returning them:
class MathOperations
{
public static void MultiplyByTwo(double value)
{
double result = value * 2;
Console.WriteLine("Multiplying by 2: {0} gives {1}", value, result);
}
}
public static void Square(double value)
{
double result = value * value;
Console.WriteLine("Squaring: {0} gives {1}", value, result);
}
code snippet MulticastDelegates/MathOperations.cs
To accommodate this change, you also have to rewrite ProcessAndDisplayNumber:
static void ProcessAndDisplayNumber(Action action, double value)
{
Console.WriteLine();
Console.WriteLine("ProcessAndDisplayNumber called with value = {0}", value);
action(value);
}
Now you can try out your multicast delegate like this:
static void Main()
{
Action operations = MathOperations.MultiplyByTwo;
operations += MathOperations.Square;
}
ProcessAndDisplayNumber(operations, 2.0);
ProcessAndDisplayNumber(operations, 7.94);
ProcessAndDisplayNumber(operations, 1.414);
Console.WriteLine();
Now, each time ProcessAndDisplayNumber is called, it will display a message to say that it has been
called. Then the following statement will cause each of the method calls in the action delegate instance to
be called in succession:
action(value);
Running this code produces this result:
MulticastDelegate
ProcessAndDisplayNumber called with value = 2
Multiplying by 2: 2 gives 4
Squaring: 2 gives 4
ProcessAndDisplayNumber called with value = 7.94
Multiplying by 2: 7.94 gives 15.88
Squaring: 7.94 gives 63.0436
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