Part III: Building E-Commerce Applications in .NET

Creation Code-39 in .NET Part III: Building E-Commerce Applications

The code-behind file for the Defaultaspx page (C# version)

The Defaultaspx page requires a code-behind file to handle the PageLoad event and the SelectedIndexChanged event for the DataList and the GridView controls The C# version of this code-behind file is shown in Listing 5-4 If you re working in Visual Basic, you can skip this section and use the VB version of the code-behind file presented in the next section instead

Listing 5-4:

The code-behind file for the Defaultaspx page (C#)

System; SystemData; SystemConfiguration; SystemCollections; SystemWeb; SystemWebSecurity; SystemWebUI; SystemWebUIWebControls; SystemWebUIWebControlsWebParts; SystemWebUIHtmlControls;

public partial class _Default : SystemWebUIPage { protected void Page_Load(object sender, 1 EventArgs e) { if (!IsPostBack) { string CatID = RequestQueryString[ cat ]; if (CatID != null) { ddlCategorySelectedValue = CatID; } } } protected void DataList1_ SelectedIndexChanged 2 (object sender, EventArgs e) { string ProductID = DataList1SelectedValueToString()Trim(); string CatID = ddlCategorySelectedValue; ResponseRedirect( Productaspx prod= + ProductID + &cat= + CatID); }

protected void GridView1_ SelectedIndexChanged 3 (object sender, EventArgs e) { string ProductID = GridView1SelectedValueToString()Trim(); string CatID = ddlCategorySelectedValue; ResponseRedirect( Productaspx prod= + ProductID + &cat= + CatID); } } Here s a closer look at each of the methods in this code-behind file:

Page_Load: This method is called each time the page is loaded Its purpose is to set the drop-down list s selection to the category indicated by the cat query string field Note that the query string field is used only when IsPostBack is false That s because the query string field should be used only when the Defaultaspx page is posted from another page, such as the Productaspx page If the query string field were used when the Defaultaspx page posts back from itself, then any selection made by the user would be replaced by the query string field s value which isn t what you want Note also that the code checks to make sure that the cat field exists before using its value DataList1_SelectedIndexChanged: This method is called whenever the user selects an item in the DataList control, which lists the currently featured products It uses the SelectedValue property of the DataList control to extract the ID of the selected product and the SelectedValue property of the drop-down list to extract the ID of the selected category Then it calls the ResponseRedirect method to redirect to the Productaspx page, with the prod and cat query strings set to the appropriate values GridView1_SelectedIndexChanged: This method is called whenever the user selects an item in the GridView control, which lists the products for the currently selected category It works pretty much the same as the DataList1_SelectedIndexChanged method, but the product ID is extracted from the GridView control instead of the DataList control

The code-behind file for the Defaultaspx page (Visual Basic version)

The Visual Basic version of this code-behind file is shown in Listing 5-5 If you re working in C#, you can skip this section and use the C# version (presented in the previous section) instead To use the Visual Basic version, you must change the Language specification in the Page directive of the Defaultaspx file from C# to VB and change the name of the code-behind file from Defaultaspxcs to Defaultaspxvb

Listing 5-5:

The code-behind file for the Defaultaspx page (VB)

Partial Class _Default Inherits SystemWebUIPage Protected Sub Page_Load( _ ByVal sender As Object, _ ByVal e As SystemEventArgs) _ Handles MeLoad If Not IsPostBack Then Dim CatID As String CatID = RequestQueryString( cat ) If Not CatID = Nothing Then ddlCategorySelectedValue = CatID End If End If End Sub Protected Sub DataList1_SelectedIndexChanged( _ ByVal sender As Object, _ ByVal e As SystemEventArgs) _ Handles DataList1SelectedIndexChanged Dim ProductID As String Dim CatID As String ProductID = DataList1SelectedValueToString()Trim() CatID = ddlCategorySelectedValue ResponseRedirect( Productaspx prod= _ + ProductID + &cat= + CatID) End Sub