Information Technology Reference
In-Depth Information
Using the as Operator with Interfaces
The
as
operator will be covered in detail in Chapter 18, but I will mention it here as well, since
it is commonly used with interfaces.
You saw earlier that you can cast a class object reference to a reference to an interface that
it implements. If, however, you attempt the cast on a class object that does not implement the
interface, the cast operation will raise an exception. You can avoid this problem by using the
as
operator instead. It works as follows:
If the class implements the interface, the expression returns a reference to the interface.
If the class does not implement the interface, the expression returns
null
rather than
raising an exception.
The following code shows the use of the
as
operator. The first line uses the
as
operator to
obtain an interface reference from a class object. The result of the expression sets the value of
b
either to
null
or to a reference to an
ILiveBirth
interface.
The second line checks the value of
b
, and if it is not
null
, executes the command that calls
the interface member method.
Class object ref
Interface name
↓
↓
ILiveBirth b = a as ILiveBirth; // Similar to cast: (ILiveBirth)a
↑
↑
Interface ref
Operator
if (b != null)
Console.WriteLine("Baby is called: {0}", b.BabyCalled());
