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[Agust1337]

First of all its not made by me, its made by Íkay Íknur...
Anonymous Methods and Behind the Scenes
Anonymous Methods provides us to define unnamed methods and most common usage of Anonymous Methods is delegates.
For an example:

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testButton.Click += {_sender, _args) =>
{
    MessageBox.Show("This is a Anonymous Function...");
};

Simply, this statements adds an event handler to the button's click event. But what is really going on behind the scenes? Does this compiler make some extra translations?

Now, we open this application in Reflector(By clicking the open button or drag and drop the file to the treeview).



Now you see that the compiler has generated a completely different method and delegate named as

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<WindowLoaded>b__0

and

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CS$<>9_CachedAnonymousMethodDelegate1

This method includes anonymous methods inline statement.



If we put this event handler assignment into Loaded event of an WPF Window,
we can see generated IL Code like below:



Simply, in this method first, the compiler creates a delegate which takes generated static method as parameter and then adds this delegate as Button's Click event handler.

Using Local Variables in Anonymous Methods
I think using Local Variables in Anonymous Methods is the most important feature in Anonymous Methods. If we add a delegate to an event as event handler explicitly, we can't use any Local Variables inside this method which assignment operation was made in.

Lets demonstrate this scenario:

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Private void Window_Loaded(object sender, RoutedEventArgs e)
{
     int x = 10;
     double y = 198.30;
     btnLambda.Click += (_sender, _args) =>
     {
         MessageBox.Show(String.Format("This is an anonymous function 
             result={0}",(x*y)));
     };
}

In this method, the Anonymous Method uses local variables which are defined in method that event handler assignment was made in.

Now, lets take a look at the new class in the project we just made and open it in Reflector again:



In this scenario, the compiler generates a new type named

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<>c__DisplayClass1

This type includes 2 more fields which we used in Anonymous Method declaration and also it includes a method declaration that performs action that we specified in Anonymous Method declaration as we discussed in the previous section.



This is what we see in Window_Loaded Method in IL Codes:



In this method firstly, the compiler generates a new

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<>c__DisplayClass1

object then assigns the field values.
And finally, the compiler creates a delegate by giving the method which locates in

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<>c__DisplayClass1

type and adds this delegate to the Button's Click event as event handler. If we use a local object reference in an Anonymous Method, scenario will be the same. Compiler-generated type will include relevant fields in order to access the used object.

Thanks for reading this ;) Hope you learnt something of this cooll;