Introduction to Components in Font

Create USS Code 39 in Font Introduction to Components

Having come this far in the book, you may be starting to wonder what happened to the Visual part of VS .NET and VB .NET. We ve been writing code as if we had nothing better than Notepad! Fortunately, VS .NET does come with some great productivity enhancements, including wizards and designers that can make most data-related work a breeze. Now that you know the basics of ADO.NET, you ll have a better understanding of what s going on behind the scenes when you use these VS .NET features.

The fundamental concept that supports these features of the VS .NET IDE is the component. Putting out of your mind for a moment the various other meanings that have been ascribed to this word over the years, a component in VS .NET is a class that (directly or indirectly) implements the System.ComponentModel.IComponent interface. Most of the time, such a class will inherit from System.ComponentModel.Component.

A VS .NET component closely interacts with the IDE. You can drop a component onto a designer (like the Web Forms Designer) page, and it will appear as an item in a separate section on the page, below the UI elements. All of the ADO.NET classes you ve seen are components, and as such, they also cooperate with and use services provided by the designer. For example, Figure 5-1 shows a SqlConnection component that s been dropped from the Toolbox s Data tab onto an empty page.

Figure 5-1. A SqlConnection component added to an empty page When a component is placed on a designer page, it starts interacting with it, providing properties and wizards that the developer can use to configure the component. Behind the scenes, the designer works together with the component to generate source code representing the actions the developer performs. As always, the best way to understand what s going on is to build an example. Try It Out: Configure a Connection Component In this very short demonstration, you ll see what happens when you place a database component onto a form in a VS .NET designer. 1. To your FriendsReunion project, add a new web form called Components.aspx. We ll use this form to experiment with components. 2. In the Toolbox, from the Data tab, drag-and-drop a SqlConnection component onto the form. Use the Properties browser to change its Name property to cnFriends. Also, from the drop-down list next to the ConnectionString property, you can select <New Connection...> and use the Data Link dialog box to configure a new connection,

or you can use the FriendsData connection created as explained in Appendix B. (This is another advantage of creating database connections with the Server Explorer, as described in Appendix B.) 3. Switch to the Code view and take a look at the code that has been generated for you.

How It Works Components don t have a UI, so they appear in a separate section at the bottom of the page. In this example, you used the component to build the value for the ConnectionString property. After the steps you performed, the code-behind page contains the following: Public Class Components Inherits System.Web.UI.Page #Region " Web Form Designer Generated Code " 'This call is required by the Web Form Designer. <System.Diagnostics.DebuggerStepThrough()> _ Private Sub InitializeComponent() Me.cnFriends = New System.Data.SqlClient.SqlConnection ' 'cnFriends ' Me.cnFriends.ConnectionString = [YOUR_CONNECTION_STRING] End Sub Protected WithEvents cnFriends As System.Data.SqlClient.SqlConnection 'NOTE: The following placeholder declaration is required by the Web Form... 'Do not delete or move it. Private designerPlaceholderDeclaration As System.Object Private Sub Page_Init(ByVal sender As System.Object, _ ByVal e As System.EventArgs) Handles MyBase.Init 'CODEGEN: This method call is required by the Web Form Designer 'Do not modify it using the code editor. InitializeComponent() End Sub #End Region Private Sub Page_Load(ByVal sender As System.Object, _ ByVal e As System.EventArgs) Handles MyBase.Load 'Put user code to initialize the page here End Sub End Class