C# Anonymous Method

As the name implies, anonymous methods are methods without a name. You can define anonymous methods in C# using the delegate (delegate) keyword and assign them to delegate (delegate) type variables.

In an anonymous method, you do not need to specify the return type, which is inferred from the return statement within the method body.

public delegate void Print(int value);
static void Main(string[] args)
{
　　　　Print print = delegate(int val) {　
　　　　　　　　Console.WriteLine("Inside the anonymous method. Value: {0}", val);　
　　　　};
　　　　print(100);
}

Inside the anonymous method. Value:100

Anonymous method accessing external function-defined variables

Anonymous methods can access variables defined in external functions.

public delegate void Print(int value);
static void Main(string[] args)
{
　　　　int i =　10;
　　　　
　　　　Print prnt = delegate(int val) {
　　　　　　　　val　+= i;
　　　　　　　　Console.WriteLine("Anonymous method: {0}", val);　
　　　　};
　　　　prnt(100);
}

Anonymous method:110

Anonymous method as a parameter

Anonymous methods can also be passed to methods that accept delegates as parameters.

In the following example, PrintHelperMethod() uses the first parameter of the Print delegate:

public delegate void Print(int value);
class Program
{
　　　　public static void PrintHelperMethod(Print printDel, int val)
　　　　{　
　　　　　　　　val　+=　10;
　　　　　　　　printDel(val);
　　　　}
　　　　static void Main(string[] args)
　　　　{
　　　　　　　　PrintHelperMethod(delegate(int val) { Console.WriteLine("Anonymous method: {0}", val); },　100);
　　　　}
}

Anonymous method:110

Anonymous methods can be used as event handlers

saveButton.Click　+= delegate(Object o, EventArgs e)
{　
　　　　System.Windows.Forms.MessageBox.Show("Save Successfully!");　
};

C#3Version .0 introduced lambda expressions, which work like anonymous methods.

Limitations of anonymous methods

• It cannot contain jump statements such as goto, break, or continue.

• It cannot access external method's ref or out parameters.

• It cannot own or access unmanaged code.

• Cannot be used on the left side of the is operator.