Visual Basic.NET How to Program (PDF)

Chapter 20 ASP .NET, Web Forms and Web Controls 949
19 ' This call is required by the Web Form Designer
20 Private Sub InitializeComponent()
21 End Sub
22
23 Private Sub Page_Init(ByVal sender As System.Object, _
24 ByVal e As System.EventArgs) Handles MyBase.Init
25
26 InitializeComponent()
27
28 timeLabel.Text = _
29 String.Format("{0:D2}:{1:D2}:{2:D2}", _
30 DateTime.Now.Hour, DateTime.Now.Minute, _
31 DateTime.Now.Second)
32 End Sub ' Page_Init
33
34 Private Sub Page_Load(ByVal sender As System.Object, _
35 ByVal e As System.EventArgs) Handles MyBase.Load
36 ' Put user code to initialize the page here
37 End Sub ' Page_Load
38 End Class ' WebTimer
Fig. 20.5 Code-behind file for a page that displays the Web server’s time (part 2 of 2).
Notice the Imports statements in lines 5–8. These statements specify namespaces
that contain classes for developing Web-based applications. The key namespace on which
we initially focus is System.Web, which contains classes that manage client requests and
server responses. The other namespaces define the controls available and how they can be
manipulated; these are discussed throughout the chapter as they become more relevant.
Line 10 begins the class definition for WebTimer, which inherits from class Page.
This class defines the requested Web page and is located in the System.Web.UI
namespace (line 7), which contains classes pertinent to the creation of Web-based applications
and controls. Class Page also provides event handlers and objects necessary for creating
Web-based applications. In addition to the Page class (from which all Web
applications directly or indirectly inherit), System.Web.UI also includes the Control
class. This class is the base class that provides common functionality for all Web controls.