Anonymous methods

1. Before c# 2.0, delegate could be declare only using named methods.

2. C# introduced anonymous methods and same can be used for delegate.

// Create a handler for a click event

button1.Click += delegate(System.Object o, System.EventArgs e)

                   { System.Windows.Forms.MessageBox.Show("Click!"); };

or

// Create a delegate instance

delegate void Del(int x);

// Instantiate the delegate using an anonymous method

Del d = delegate(int k) { /* ... */ };

3. Benefit -We reduce the coding overhead in instantiating delegates by eliminating the need to create a separate method.
4. Another good example would be when launching a new thread. This class creates a thread and also contains the code that the thread executes, without the need for creating an additional method for the delegate.

void StartThread()

{

    System.Threading.Thread t1 = new System.Threading.Thread

      (delegate()

            {

                System.Console.Write("Hello, ");

                System.Console.WriteLine("World!");

            });

    t1.Start();

}

5. The scope of the parameters of an anonymous method is anonymous-method-block.
6. It is an error to have a jump statement, such as goto, break, or continue, inside the anonymous method block whose target is outside the block. Similarly it is also an error to have a jump statement, such as goto, break, or continue, outside the anonymous method block whose target is inside the block.
7. The local variables and parameters whose scope contain an anonymous method declaration are called outer or captured variables of the anonymous method. For example, in the following code segment, n is an outer variable:

int n = 0;

Del d = delegate() { System.Console.WriteLine("Copy #:{0}", ++n); };

8.  Unlike local variables, the lifetime of the outer variable extends until the delegates that reference the anonymous methods are eligible for garbage collection. A reference to n is captured at the time the delegate is created.
9. An anonymous method cannot access the ref or out parameters of an outer scope.
10. Two ways of instantiating a delegate:

·             Associating the delegate with an anonymous method.

·             Associating the delegate with a named method (DoWork).

In each case, a message is displayed when the delegate is invoked.

// Declare a delegate

delegate void Printer(string s);

class TestClass

{

    static void Main()

    {

        // Instatiate the delegate type using an anonymous method:

        Printer p = delegate(string j)

        {

            System.Console.WriteLine(j);

        };

        // Results from the anonymous delegate call:

        p("The delegate using the anonymous method is called.");

        // The delegate instantiation using a named method "DoWork":

        p = new Printer(TestClass.DoWork);

        // Results from the old style delegate call:

        p("The delegate using the named method is called.");

    }

    // The method associated with the named delegate:

    static void DoWork(string k)

    {

        System.Console.WriteLine(k);

    }

}

Output

The delegate using the anonymous method is called.

The delegate using the named method is called.