Binding Data to a Web Forms DataList

Problem

You need to bind the result set from a query to a DataList control.

Solution

Set the DataList 's advanced properties as demonstrated by this solution.

The schema of table TBL0703 that is used in the solution is shown in Table 7-2.

Table 7-2. TBL0703 schema

Column name	Data type	Length	Allow nulls?
Id	int	4	No
IntField	int	4	Yes
StringField	nvarchar	50	Yes

The Web Forms page sample code defines the DataList control and the three templates SelectedItemTemplate , ItemTemplate , and EditItemTemplate which control the display of data for selected items, unselected items, and items being edited. The static Eval( ) method of the DataBinder class is used to fill the field values in each template. Container.DataItem specifies the container argument for the method which when used in a list in a template resolves to DataListItem.DataItem . The code for the Web Forms page is shown Example 7-5.

Example 7-5. File: ADOCookbookCS0703.aspx

 
 
 
 
 <%# DataBinder.Eval(Container.DataItem, "Id") %>;
 <%# DataBinder.Eval(Container.DataItem, "IntField") %>;
 <%# DataBinder.Eval(Container.DataItem, "StringField") %>
 
 
 
 
 
 <%# DataBinder.Eval(Container.DataItem, "Id") %>;
 <%# DataBinder.Eval(Container.DataItem, "IntField") %>;
 <%# DataBinder.Eval(Container.DataItem, "StringField") %>
 
 
 
 
 
 
 
 
 

 ID: 
 
 
 

 IntField: 
 
 
 

 StringField: 
 
 
 

The code-behind contains six event handlers and three methods :

Page.Load

Calls the CreateDataSource( ) method and binds data to the Web Forms DataList , if the page is being loaded for the first time.

CreateDataSource( )

This method fills a DataTable with the TBL0703 table and stores the DataTable to a Session variable to cache the data source for the DataList .

UpdateDataSource( )

This method creates a DataAdapter and uses it together with updating logic generated by a CommandBuilder to update the data source with changes made to the cached DataTable . The updated DataTable is stored to the Session variable, which is used to cache the data source for the DataList .

BindDataList( )

This method gets the cached data from the Session variable and binds its default view to the DataList .

DataList.CancelCommand

Sets the index of the item being edited to -1 to cancel any current editing and calls BindDataList( ) to refresh the list.

DataList.DeleteCommand

Finds and deletes the specified row from the data cached in the Session variable and calls the UpdateDataSource( ) method to persist the change back to the data source. BindDataList( ) is called to refresh the list.

DataList.EditCommand

Sets the index of the selected item to -1 to cancel its selection. The index of the item being edited is then set to the index of the row corresponding to the Edit button putting that row into edit mode. BindDataList( ) is called to refresh the list.

DataList.ItemCommand

Checks if the Select button was pressed. If it was, the index of the item being edited is set to -1 to cancel its editing. The index of the selected item is then set to the index of the row corresponding to the Select button to put that row into select mode. Finally, BindDataList( ) is called to refresh the list.

DataList.UpdateCommand

Finds and updates the specified row in the data cached in the Session variable and calls the UpdateDataSource( ) method to persist the change back to the data source. BindDataList( ) is called to refresh the list.

The C# code for the code-behind is shown in Example 7-6.

Example 7-6. File: ADOCookbookCS0703.aspx.cs

// Namespaces, variables, and constants
using System;
using System.Configuration;
using System.Web.UI.WebControls;
using System.Data;
using System.Data.SqlClient; 

private const String TABLENAME = "TBL0703"; 

// . . . 

private void Page_Load(object sender, System.EventArgs e)
{
 if(!Page.IsPostBack)
 {
 dataList.DataSource = CreateDataSource( );
 dataList.DataKeyField = "Id";
 dataList.DataBind( );
 }
}

private DataTable CreateDataSource( )
{
 DataTable dt = new DataTable(TABLENAME);

 // Create the DataAdapter and fill the table using it.
 SqlDataAdapter da = new SqlDataAdapter("SELECT * FROM " + TABLENAME +
 " ORDER BY Id",
 ConfigurationSettings.AppSettings["DataConnectString"]);
 da.Fill(dt);
 da.FillSchema(dt, SchemaType.Source);

 // Store data in session variable to store data between
 // posts to server.
 Session["DataSource"] = dt;

 return dt;
}

private DataTable UpdateDataSource(DataTable dt)
{
 // Create a DataAdapter for the update.
 SqlDataAdapter da = new SqlDataAdapter("SELECT * FROM " + TABLENAME +
 " ORDER BY Id",
 ConfigurationSettings.AppSettings["DataConnectString"]);
 // Create a CommandBuilder to generate update logic.
 SqlCommandBuilder cb = new SqlCommandBuilder(da);

 // Update the data source with changes to the table.
 da.Update(dt);

 // Store updated data in session variable to store data between
 // posts to server.
 Session["DataSource"] = dt;

 return dt;
}

private void BindDataList( )
{
 // Get the data from the session variable.
 DataView dv = ((DataTable)Session["DataSource"]).DefaultView;

 // Bind the data view to the data list.
 dataList.DataSource = dv;
 dataList.DataBind( );
}

private void dataList_CancelCommand(object source,
 System.Web.UI.WebControls.DataListCommandEventArgs e)
{
 // Set the index of the item being edited out of range.
 dataList.EditItemIndex = -1;

 BindDataList( );
}

private void dataList_DeleteCommand(object source,
 System.Web.UI.WebControls.DataListCommandEventArgs e)
{
 // Get the data from the session variable.
 DataTable dt = (DataTable)Session["DataSource"];

 // Get the ID of the row to delete.
 int id = (int)dataList.DataKeys[e.Item.ItemIndex];

 // Delete the row from the table.
 dt.Rows.Find(id).Delete( );

 // Update the data source with the changes to the table.
 UpdateDataSource(dt);

 // Set the index of the item being edited out of range.
 dataList.EditItemIndex = -1;

 BindDataList( );
}

private void dataList_EditCommand(object source,
 System.Web.UI.WebControls.DataListCommandEventArgs e)
{
 // Set the index of the selected item out of range.
 dataList.SelectedIndex = -1;
 // Set the index of the item being edited to the current record.
 dataList.EditItemIndex = e.Item.ItemIndex;

 BindDataList( );
}

private void dataList_ItemCommand(object source,
 System.Web.UI.WebControls.DataListCommandEventArgs e)
{
 // Check if the "select" button is pressed.
 if (e.CommandName == "Select")
 {
 // Set the index of the item being edited out of range.
 dataList.EditItemIndex = -1;
 // Set the index of the selected item to the current record.
 dataList.SelectedIndex = e.Item.ItemIndex;

 BindDataList( );
 } 
}

private void dataList_UpdateCommand(object source,
 System.Web.UI.WebControls.DataListCommandEventArgs e)
{
 // Get the data from the session variable.
 DataTable dt = (DataTable)Session["DataSource"];

 // Get the ID of the row to update.
 int id = (int)dataList.DataKeys[e.Item.ItemIndex];

 // Get the DataRow to update using the ID.
 DataRow dr = dt.Rows.Find(id);

 // Get the column values for the current record from the DataList.
 dr["IntField"] =
 Int32.Parse(((TextBox)e.Item.FindControl("intFieldTextBox")).Text);
 dr["StringField"] =
 ((TextBox)e.Item.FindControl("stringFieldTextBox")).Text;

 // Update the data source with the changes to the table.
 UpdateDataSource(dt);

 // Set the index of the item being edited out of range.
 dataList.EditItemIndex = -1;
 
 BindDataList( );
}

Discussion

The DataList Web Forms control displays tabular data from a data source and controls the formatting using templates and styles. The DataList must be bound to a data source such as a DataReader , DataSet , DataTable , or DataView any class that implements the IEnumerable interface can be bound. The easiest way to create a DataList control is to drag the DataList control onto the web page design surface.

The DataList Web Form control uses templates to display items, control layout, and provide functional capabilities. Table 7-3 describes the different templates for the DataList .

Table 7-3. DataList templates

Template	Description
AlternatingItemTemplate	Elements to render for every other row in the control. This is normally used to specify a different display style for alternating rows. This template is defined within the and tags.
EditItemTemplate	Elements to render when an item is put into edit mode. This template is invoked for the row specified in the EditItemIndex property; setting the EditItemIndex property to -1 cancels the edit mode. This template is defined within the and tags.
FooterTemplate	Elements to render at the bottom of the control. The footer template cannot be data bound. This template is defined within the and tags.
HeaderTemplate	Elements to render at the top of the control. The header template cannot be data bound. This template is defined within the and tags.
ItemTemplate	Elements to render for each row in the data source. This template is defined within the and tags.
SelectedItemTemplate	Elements to render when an item in the control is selected. This template is invoked for the row specified by the SelectedIndex property; setting the SelectedIndex property to -1 cancels the select mode. This template is defined within the and tags.
SeparatorTemplate	Elements to render between each item. The SeparatorTemplate cannot be data bound. This template is defined within the and tags.

To format the templates, right-click on the DataList control on the design surface and select one of the three editing submenus of the Edit Template menu. To end editing, right-click the DataList control and select End Template Editing. Templates can also be customized by editing the HTML directly. One of the item templates must contain a data bound control for the DataList control to render at runtime.

A Button , LinkButton , or ImageButton web server control can be added to the control templates. These buttons can let the user switch between the different item modes, for example. The buttons bubble their events to the containing DataList control. The events that the DataList raises in response to button clicks on the list items are described in Table 7-4.

Table 7-4. DataList Button click events

Event	Description
CancelCommand	Raised when the Cancel button is clicked for an item in the control.
DeleteCommand	Raised when the Delete button is clicked for an item in the control.
EditCommand	Raised when the Edit button is clicked for an item in the control.
ItemCommand	Raised when any button is clicked for an item in the control. The button clicked can be determined by reading the CommandName property of the DataListCommandEventArgs object in the ItemCommand event handler. This property contains the value of CommandName property of the button that was clicked.
UpdateCommand	Raised when the Update button is clicked for an item in the control.

After the properties appropriate to the control are set, call the DataBind( ) method of the control or of the page to bind the data source to the server control.