Programming ASP.NET: Custom and User Controls, Part 1
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Adding Code

So far, all you've put into the user control is straight HTML. This is simple, but also somewhat limited. There is no reason to so severely limit the user control. In the next example, you'll add support for filling the list box with books from a database. To do so, you'll need to add a table to the ProgASPNetBugs database, as shown in Figure 14-2.

Figure 14-2. Design of the Books table

You'll also need to populate this table with the values shown in Figure 14-3, or simply download the entire database with data already provided.

Figure 14-3. Contents of the Books table

You are ready to fill the list box dynamically, using data binding. Strip out all the code that fills the list box by hand. This reduces Example 14-3 to two lines:

<ASP:DropDownList id=ddlBooks runat=server>
</ASP:DropDownList>

The key to making this work is now in the Control tag:

<%@ Control Language="c#" AutoEventWireup="false" 
Codebehind="BookList.ascx.cs" 
Inherits="UserControl1.WebUserControl1"%>

The Codebehind attribute points to the code-behind page. In that page, you'll add code to the Page_Load method to bind the list box to the appropriate table in the database. That code is shown in Example 14-4 for C# and Example 14-5 for VB.NET.

Example 14-4: C# Page_Load from the code-behind page for the user control

private void Page_Load(object sender, System.EventArgs e)
{
   if (!IsPostBack)
   {
      string connectionString = 
         "server= " + ServerName + 
         "; uid=sa;pwd=" +
         Password + "; database= " + DB;
 
      // get records from the Bugs table
      string commandString = 
         "Select BookName from Books";
 
      // create the data set command object 
      // and the DataSet
      SqlDataAdapter dataAdapter = 
         new SqlDataAdapter(
         commandString, connectionString);
 
      DataSet dataSet = new DataSet(  );
 
      // fill the data set object
      dataAdapter.Fill(dataSet,"Bugs");
 
      // Get the one table from the DataSet
      DataTable dataTable = dataSet.Tables[0];
 
      ddlBooks.DataSource = dataTable.DefaultView;
      ddlBooks.DataTextField = "BookName";
      ddlBooks.DataBind(  );
   }
}

Example 14-5: VB.NET Page_Load from the code-behind page for the user control

Private Sub Page_Load(ByVal sender As System.Object, _
                      ByVal e As System.EventArgs) Handles MyBase.Load
   If Not IsPostBack Then
      Dim connectionString As String = _
               "server= " & ServerName & 
               "; uid=sa;pwd=" +
               Password + "; database= " + DB;
 
            ' get records from the Bugs table
            Dim commandString As String = _
               "Select BookName from Books"
 
            ' create the data set command object 
            ' and the DataSet
             Dim dataAdapter as SqlDataAdapter = _
               new SqlDataAdapter( _
               commandString, connectionString);
 
            Dim dataSet As DataSet = New DataSet(  )
 
            ' fill the data set object
            dataAdapter.Fill(dataSet, "Books")
 
            ' Get the one table from the DataSet
            Dim dataTable As DataTable = dataSet.Tables(0)
 
            ddlBooks.DataSource = dataTable.DefaultView
            ddlBooks.DataTextField = "BookName"
            ddlBooks.DataBind(  )
        End If
    End Sub

The host page does not change at all. The updated user control now works as intended, loading the list of books from the database, as shown in Figure 14-4.

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