BoundColumns

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BoundColumns

In the previous examples, the DataGrid has been bound to a data source and the columns have been created dynamically based on the columns in the DataTable . BoundColumns can be used to create a custom column layout for the DataGrid . Each BoundColumn can define the column heading text and the field in the table to sort on. Like all controls in ASP.NET, BoundColumns includes basic properties such as Visible , among others. In Chapter 7, "Working with ASP.NET Server Controls Templates," you'll learn about other properties of BoundColumns . This chapter covers only the basic properties.

BoundColumns are encapsulated inside a property declaration. The DataGrid property is named Columns . Each BoundColumn renders a table column populated with the data from the data source specified by a DataField property. Listing 6.12 shows the DataGrid code to use BoundColumns with the programmatic code from Listing 6.11.

Listing 6.12 Using BoundColumns with the DataGrid

 [Web Form VB & C#] 16: <asp:DataGrid runat="server" id="myDataGrid" 17:   Width="740" 18:   Cellpadding="4" 19:   Cellspacing="0" 20:   Gridlines="Horizontal" 21:   HorizontalAlign="Center" 22:   HeaderStyle-CssClass="tableHeader" 23:   ItemStyle-CssClass="tableItem" 24:   AlternatingItemStyle-CssClass="alternatingItem" 25:   AllowPaging="True" 26:   OnPageIndexChanged="PageIndexChanged_OnClick" 27:   PageSize="10" 28:   PagerStyle-Mode="NumericPages" 29:   PagerStyle-HorizontalAlign="Right" 30:   PagerStyle-CssClass="pageLinks" 31:   AllowSorting="True" 32:   OnSortCommand="SortCommand_OnClick" 33:   AutoGenerateColumns="False" 34:  > 35:  <Columns> 36:   <asp:BoundColumn DataField="CompanyName" 37     HeaderText="Company Name" SortExpression="CompanyName" /> 38:   <asp:BoundColumn DataField="ContactName" 39:    HeaderText="Contact Name" SortExpression="ContactName" /> 40:   <asp:BoundColumn DataField="ContactTitle" 41:    HeaderText="Contact Title" SortExpression="ContactTitle" /> 42:   <asp:BoundColumn DataField="Phone" HeaderText="Phone" /> 43:   <asp:BoundColumn DataField="Fax" HeaderText="Fax" /> 44:  </Columns> 45:  </asp:DataGrid> 

In Listing 6.12, you modify the DataGrid properties to use BoundColumns . The benefit of using BoundColumns is that you can specify the column heading text ( HeaderText ) and the name of the field to sort on ( SortExpression ). In Listing 6.12, you add spaces to column names that are two words (such as Company Name , Contact Name , and Contact Title ), and disable sorting on the Phone and Fax columns by not adding a SortExpression value to those columns.

On line 33, you add the AutoGenerateColumns property to the DataGrid and set it to False . This tells the .NET Framework that you'll specify how the columns are generated. If AutoGenerateColumns is set to True , the BoundColumns you specify will be rendered, followed by all the columns in the data source. True is the default value.

Each BoundColumn specifies a DataField property (lines 37, 39, 41, 42, and 43). This is the name of the field in the data source that the BoundColumn will display when data-bound. Additionally, you specify the HeaderText property and a SortExpression property. For the Phone (line 42) and Fax (line 43) columns, no SortExpression is specified. The .NET Framework will disable sorting on a column when BoundColumns are used and no SortExpression is specified. Figure 6.11 shows the rendered page from Listing 6.12.

Figure 6.11. Using BoundColumns in a DataGrid , you can specify the column order, the column heading text, and the field to sort on.

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