Beginning ASP.NET 4.5 in CSharp and VB Opsylum

198 x CHAPTER 5 PROGRAMMING YOUR ASP.NET WEB PAGES
Figure 5-7 shows that Person inherits from Object (indicated by the arrow pointing in the direction
of the class that is being inherited from), which in turn means that a Person instance can do whatever
an Object can do. So, for example, you can call ToString() on your Person object:
Label1.Text = myPerson.ToString()
' Writes out Person
The default behavior of the ToString() method defined in Object is to say its own class name. In
the preceding example, it means that the Person class inherits this behavior and thus says Person
as its name. Usually, this default behavior is not enough, and it would be much more useful if the
Person could return the full name of the person it is representing, for example. You can easily do
this by overriding the ToString() method. Overriding a method or property redefines the behavior
the class inherits from its parent class. To override a method you use the keyword Overrides
in VB.NET and override in C#. The following snippet redefines the behavior of ToString in the
Person class:
VB.NET
Public Overrides Function ToString() As String
Return FullName & ", born at " & _dateOfBirth.ToShortDateString()
End Function
C#
public override string ToString()
{
return FullName + ", born at " + _dateOfBirth.ToShortDateString();
}
With this definition of ToString in the Person class, it no longer returns the word Person, but now
returns the full name of the person it is representing:
Label1.Text = myPerson.ToString() ' Imar Spaanjaars, born at 8/9/1971
Notice how the code uses the read-only FullName property to avoid coding the logic of concatenating
the two names again. You can’t just override any method member you want to. For a method
to be overridable, the parent class needs to mark the member with the keyword virtual (in C#) or
Overridable (in VB.NET).
Object inheritance in .NET enables you to create a hierarchy of objects that enhance, or add functionality
to, other objects. This enables you to start out with a generic base class (Object). Other
classes can then inherit from this class, adding specialized behavior. If you need even more specialized
classes, you can inherit again from the class that inherits from Object, thus creating a hierarchy
of classes that keep getting more specialized. This principle works for many classes in the .NET
Framework, including the Page class. You may not realize it, but every ASPX page you create in VS
is actually a class that inherits from the class System.Web.UI.Page. This Page class in turn inherits
from TemplateControl, which inherits from Control, which inherits from Object. The entire
hierarchy is shown in Figure 5-8. At the bottom you see the class MyWebPage, which could be a Code
Behind class of a page such as MyWebPage.aspx.