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var data = new DataSet();

var adapter = new SqlDataAdapter(commandText, connectionString);

adapter.Fill(data);

// Table is the default name of the first table in a

// DataSet filled by an adapter

grid.DataMember = "Table";

grid.DataSource = data;

grid.DataBind();

DataMember and DataSource can be set in any order, provided that both are set before DataBind is invoked. DataMember has no relevance if you bind to data using DataSourceID with standard data source components.

The DataTextField Property

Typically used by list controls, the DataTextField property specifies which property of a data-bound item should be used to define the display text of the nth element in a list control:

public virtual string DataTextField {get; set;}

For example, for a drop-down list control the property feeds the displayed text of each item in the list. The following code creates the control shown in Figure 10-2:

CountryList.DataSource = data;

CountryList.DataTextField = "country";

CountryList.DataBind();

Figure 10-2. A drop-down list control filled with the country column of a database table.

An analogous behavior can be observed for other list controls, such as ListBox and CheckBoxList.

Note

List controls can automatically format the content of the field bound through the DataTextField property. The format expression is indicated via the DataTextFormatString property.

The DataValueField Property

Similar to DataTextField, the DataValueField property specifies which property of a data-bound item should be used to identify the nth element in a list control:

public virtual string DataValueField {get; set;}

To understand the role of this property, consider the markup generated for a drop-down list, set as in the code snippet shown previously:

[All]

Argentina

Austria

...

The text of each tag is determined by the field specified through DataTextField; the value of the value attribute is determined by DataValueField. Consider the following code that fills a ListBox with customer names:

CustomerList.DataMember = "Table";

CustomerList.DataTextField = "companyname";

CustomerList.DataValueField = "customerid";

CustomerList.DataSource = data;

CustomerList.DataBind();

If DataValueField is left blank, the value of the DataTextField property is used instead. Here’s the corresponding markup:

Bottom-Dollar Markets

Laughing Bacchus Wine Cellars

...

As you can see, the value attribute now is set to the customer ID—the unique, invisible value determined by the customerid field. The content of the value attribute for the currently selected item is returned by the SelectedValue property of the list control. If you want to access programmatically the displayed text of the current selection, use the SelectedItem.Text expression.

The AppendDataBoundItems Property

This Boolean property indicates whether the data-bound items should be appended to the existing contents of the control or whether they should overwrite them. By default, AppendDataBoundItems is set to false, meaning that data-bound contents replace any existing contents.

public virtual bool AppendDataBoundItems {get; set;}

AppendDataBoundItems is useful when you need to combine constant items with data-bound items. For example, imagine you need to fill a drop-down list with all the distinct countries/regions in which you have a customer. The user will select a country/region and see the list of customers who live there. To let users see all the customers in any country/region, you add an unbound element, such as [All].

AppendDataBoundItems="true">

With AppendDataBoundItems