How to add static items and results from data binding to a DropDownList control by using Visual C# .NET (312489)

MORE INFORMATION

Create an ASP.NET Web application by using Visual C# .NET

1. Open Microsoft Visual Studio .NET.
2. On the File menu, point to New, and then click Project.
3. In the New Project dialog box, click Visual C# Projects under Project Types, and then click ASP.NET Web Application under Templates.
4. In the Location box, replace WebApplication1 in the default URL with DDLSample. If you are using the local server, you can leave the server name as http://localhost so that the Location box displays http://localhost/DDLSample.

Create the sample

1. To add a Web Form to the project, follow these steps:
   1. Right-click the project node in Solution Explorer, click Add, and then click Add Web Form.
   2. Name the .aspx page DropDown.aspx, and then click Open.
2. Make sure that the page is open in Design view in the editor. Add a DropDownList control to the page. In the Properties pane, change the ID of the control to AuthorList.
3. Add a Label control to the page after the DropDownList control. In the Properties pane, change the ID of the control to CurrentItem.
4. Add a Button control to the page after the Label control. In the Properties pane, change the ID of the control to GetItem, and then change the Text property to Get Item.
5. Right-click the page, and then click View Code. This opens the code-behind class file in the editor.
6. Add the System.Data.SqlClient namespace to the code-behind class file so that the sample code functions properly. The complete list of namespaces should appear as follows.

   using System;
   using System.Collections;
   using System.ComponentModel;
   using System.Data;
   using System.Drawing;
   using System.Web;
   using System.Web.SessionState;
   using System.Web.UI;
   using System.Web.UI.WebControls;
   using System.Web.UI.HtmlControls;
   using System.Data.SqlClient;
   					

7. Add the following code to the Page_Load event.

   private void Page_Load(object sender, System.EventArgs e)
           {
               if(!IsPostBack)
               {
                   SqlConnection myConn = new SqlConnection(
                       "Server=localhost;Database=Pubs;Integrated Security=SSPI");
                   SqlCommand myCmd = new SqlCommand(
                       "SELECT au_id, au_lname FROM Authors", myConn);
                   myConn.Open();
                   SqlDataReader myReader = myCmd.ExecuteReader();
   			
                   //Set up the data binding.
                   AuthorList.DataSource = myReader;
                   AuthorList.DataTextField = "au_lname";
                   AuthorList.DataValueField = "au_id";
                   AuthorList.DataBind();
   			
                   //Close the connection.
                   myConn.Close();
                   myReader.Close();
   
                   //Add the item at the first position.
                   AuthorList.Items.Insert(0, "<-- Select -->");
   				
               }
   
           }
   					

   To use Integrated Security in the connect string, change the Web.config file for the application and set the impersonate attribute of the identity configuration element to true, as shown in the following example.

   <configuration>
     <system.web>
       <identity impersonate="true" />
     </system.web>
   </configuration>

   For more information about ASP.NET Impersonation, visit the following Microsoft Developer Network (MSDN) Web site:

   http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpguide/html/cpconaspnetimpersonation.asp

8. Modify the connection string as appropriate for your environment.
9. Switch to the Design view in the editor for the .aspx page. Double-click GetItem. Add the following code to the GetItem_Click event in the code-behind class file.

   private void GetItem_Click(object sender, System.EventArgs e)
           {
               string itemText = AuthorList.SelectedItem.Text;
               string itemValue = AuthorList.SelectedItem.Value;
               CurrentItem.Text = string.Format(
                   "Selected Text is {0}, and Value is {1}", itemText, itemValue);
           }
   					

10. On the File menu, click Save All to save the Web Form and other associated project files.
11. On the Build menu in the Visual Studio .NET Integrated Development Environment (IDE), click Build to build the project.
12. In Solution Explorer, right-click the .aspx page, and then click View In Browser. Notice that the page opens in the browser and that the drop-down list box is populated with the initial data.
13. Click an item in the drop-down list box. Notice that the CurrentItem Label control displays the item that you selected. In addition, notice that the list retains the current position and the static entry.

Troubleshooting

• You must place the code to add the static item to the ListItem collection of the control after the data binding code. If you do not add the code in this order, the list is re-created with the data binding code, which overwrites the static entry.
• The sample code checks the IsPostBack property to prevent the list from being re-created. In addition, this code checks IsPostBack to retain the selected item in the current position of the list between round trips to the server.