advantage of 'as' key word in c#

There are two safe ways to check if an object is of the type you expect: as and is. The third way is to use a cast and see it it throws an exception, but that is a bad practice and should be avoided.

The difference is that is just check, and returns true or false, while as converts, and returns null if it isn't a type in the object inheritance.

So you can do it two ways:

if (obj is myType)
   {
   MyType mt = (MyTpe) obj;
   ...
   }

Or

MyType mt = obj as MyType;
if (mt != null)
   {
   ...
   }

I prefer the second as it includes an explicit null check.

We can use this in common routines, for example a Click event handler that could come from a variety of sources:

private void button1_Click(object sender, EventArgs e)
    {
    Button b = sender as Button;
    if (b != null)
        {
        ...
        }
    }

If it isn't a button, then we may not know what to do with it!

The as operator is used to perform conversions between types that are compatible. Used in an expression with the form:

expression as type

The expression is a reference type and the type is a reference type

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