DataGrid.Columns Property
Gets a collection of objects that represent the columns of the DataGrid control.
Assembly: System.Web (in System.Web.dll)
<PersistenceModeAttribute(PersistenceMode.InnerProperty)> Public Overridable ReadOnly Property Columns As DataGridColumnCollection
Property Value
Type: System.Web.UI.WebControls.DataGridColumnCollectionA DataGridColumnCollection object that contains a collection of objects that represent the columns of the DataGrid control.
Use this property to programmatically control the collection of columns in the DataGrid control. The Columns collection contains explicitly declared columns that get rendered in the DataGrid control.
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Explicitly declared columns may be used in conjunction with automatically generated columns. When using both, explicitly declared columns will be rendered first, followed by the automatically generated columns. Automatically generated columns are not added to the Columns collection. |
The order that the columns are displayed in the DataGrid control is controlled by the order that the columns appear in the Columns collection.
The following table shows the different column classes that derive from the DataGridColumn class and can be used in the Columns collection.
Column type | Description |
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Displays a column bound to a field in a data source. It displays each item in the field as text. This is the default column type of the DataGrid control. | |
Displays a command button for each item in the column. This allows you to create a column of custom button controls, such as the Add or Remove button. | |
Displays a column that contains editing commands for each item in the column. | |
Displays the contents of each item in the column as a hyperlink. The contents of the column can be bound to a field in a data source or static text. | |
Displays each item in the column following a specified template. This allows you to provide custom controls in the column. |
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Although you can programmatically add columns to the Columns collection, it is easier to list the columns statically and then use the Visible property to show or hide the column. |
The following code example demonstrates how to use the Columns collection to dynamically add a column to the DataGrid control.
<%@ Page Language="VB" AutoEventWireup="True" %> <%@ Import Namespace="System.Data" %> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" > <script language="VB" runat="server"> Dim Cart As DataTable Dim CartView As DataView Function CreateDataSource() As ICollection Dim dt As New DataTable() Dim dr As DataRow dt.Columns.Add(New DataColumn("IntegerValue", GetType(Int32))) dt.Columns.Add(New DataColumn("StringValue", GetType(String))) dt.Columns.Add(New DataColumn("CurrencyValue", GetType(Double))) Dim i As Integer For i = 0 To 8 dr = dt.NewRow() dr(0) = i dr(1) = "Item " & i.ToString() dr(2) = 1.23 *(i + 1) dt.Rows.Add(dr) Next i Dim dv As New DataView(dt) Return dv End Function 'CreateDataSource Sub Page_Load(sender As Object, e As EventArgs) If Session("DG4_ShoppingCart") Is Nothing Then Cart = New DataTable() Cart.Columns.Add(New DataColumn("Item", GetType(String))) Cart.Columns.Add(New DataColumn("Price", GetType(String))) Session("DG4_ShoppingCart") = Cart Else Cart = CType(Session("DG4_ShoppingCart"), DataTable) End If CartView = New DataView(Cart) ShoppingCart.DataSource = CartView ShoppingCart.DataBind() If Not IsPostBack Then ' Load this data only once. ItemsGrid.DataSource = CreateDataSource() ItemsGrid.DataBind() End If End Sub 'Page_Load Sub Page_Init(sender As Object, e As EventArgs) ' Create a dynamic column to add to Columns collection. Dim NumberColumn As New BoundColumn() NumberColumn.HeaderText = "Item Number" NumberColumn.DataField = "IntegerValue" ' Add column to Columns collection. ItemsGrid.Columns.AddAt(2, NumberColumn) End Sub 'Page_Init Sub Grid_CartCommand(sender As Object, e As DataGridCommandEventArgs) Dim dr As DataRow = Cart.NewRow() ' e.Item is the table row where the command is raised. ' For bound columns, the value is stored in the Text property of the TableCell. Dim itemCell As TableCell = e.Item.Cells(2) Dim priceCell As TableCell = e.Item.Cells(3) Dim item As String = itemCell.Text Dim price As String = priceCell.Text If CType(e.CommandSource, Button).CommandName = "AddToCart" Then dr(0) = item dr(1) = price Cart.Rows.Add(dr) Else 'Remove from Cart. CartView.RowFilter = "Item='" & item & "'" If CartView.Count > 0 Then CartView.Delete(0) End If CartView.RowFilter = "" End If ShoppingCart.DataBind() End Sub 'Grid_CartCommand </script> <head runat="server"> <title>DataGrid Columns Example</title> </head> <body> <form id="form1" runat="server"> <h3>DataGrid Columns Example</h3> <table cellpadding="5"> <tr valign="top"> <td> <b>Product List</b> <asp:DataGrid id="ItemsGrid" BorderColor="black" BorderWidth="1" CellPadding="3" AutoGenerateColumns="false" OnItemCommand="Grid_CartCommand" runat="server"> <HeaderStyle BackColor="#00aaaa"> </HeaderStyle> <Columns> <asp:ButtonColumn HeaderText="Add to cart" ButtonType="PushButton" Text="Add" CommandName="AddToCart"/> <asp:ButtonColumn HeaderText="Remove from cart" ButtonType="PushButton" Text="Remove" CommandName="RemoveFromCart"/> <asp:BoundColumn HeaderText="Item" DataField="StringValue"/> <asp:BoundColumn HeaderText="Price" DataField="CurrencyValue" DataFormatString="{0:c}"> <ItemStyle HorizontalAlign="right"> </ItemStyle> </asp:BoundColumn> </Columns> </asp:DataGrid> </td> <td> <b>Shopping Cart</b> <asp:DataGrid id="ShoppingCart" runat="server" BorderColor="black" BorderWidth="1" GridLines="Both" ShowFooter="false" CellPadding="3" CellSpacing="0"> <HeaderStyle BackColor="#00aaaa"> </HeaderStyle> </asp:DataGrid> </td> </tr> </table> </form> </body> </html>
<%@ Page Language="VB" AutoEventWireup="True" %> <%@ Import Namespace="System.Data" %> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" > <script runat="server"> Function CreateDataSource() As ICollection ' Create sample data for the DataGrid control. Dim dt As DataTable = New DataTable() Dim dr As DataRow ' Define the columns of the table. dt.Columns.Add(New DataColumn("IntegerValue", GetType(Int32))) dt.Columns.Add(New DataColumn("StringValue", GetType(string))) dt.Columns.Add(New DataColumn("CurrencyValue", GetType(double))) ' Populate the table with sample values. Dim i As Integer For i = 0 to 4 dr = dt.NewRow() dr(0) = i dr(1) = "Item " & i.ToString() dr(2) = 1.23 * (i + 1) dt.Rows.Add(dr) Next i Dim dv As DataView = New DataView(dt) Return dv End Function Sub Page_Load(sender As Object, e As EventArgs) ' Load sample data only once, when the page is first loaded. If Not IsPostBack Then ItemsGrid.DataSource = CreateDataSource() ItemsGrid.DataBind() End If End Sub Sub Button_Click(sender As Object, e As EventArgs) ' Count the number of selected items in the DataGrid control. Dim count As Integer = 0 ' Display the selected times. Message.Text = "You Selected: <br />" ' Iterate through each item (row) in the DataGrid control and ' determine whether it is selected. Dim item As DataGridItem For Each item In ItemsGrid.Items DetermineSelection(item, count) Next ' If no items are selected, display the appropriate message. If count = 0 Then Message.Text = "No items selected" End If End Sub Sub DetermineSelection(item As DataGridItem, ByRef count As Integer) ' Retrieve the SelectCheckBox CheckBox control from the ' specified item (row) in the DataGrid control. Dim selection As CheckBox = _ CType(item.FindControl("SelectCheckBox"), CheckBox) ' If the item is selected, display the appropriate message and ' increment the count of selected items. If Not selection Is Nothing Then If selection.Checked Then Message.Text &= "- " & item.Cells(1).Text & "<br />" count = count + 1 End If End If End Sub Sub Check_Change(sender As Object, e As EventArgs) ' Show or hide the first column depending on the value of ' the check box. If ShowCheckBox.Checked Then ItemsGrid.Columns(0).Visible = True Else ItemsGrid.Columns(0).Visible = False End If End Sub </script> <head runat="server"> <title>DataGridColumn Visible Example</title> </head> <body> <form id="form1" runat="server"> <h3>DataGridColumn Visible Example</h3> Select whether to show or hide the first column. <br /><br /> <b>Product List</b> <asp:DataGrid id="ItemsGrid" BorderColor="black" BorderWidth="1" CellPadding="3" ShowFooter="True" AutoGenerateColumns="False" runat="server"> <HeaderStyle BackColor="#00aaaa"> </HeaderStyle> <FooterStyle BackColor="#00aaaa"> </FooterStyle> <Columns> <asp:BoundColumn DataField="IntegerValue" Visible="True" HeaderText="Item"/> <asp:BoundColumn DataField="StringValue" Visible="True" HeaderText="Description"/> <asp:BoundColumn DataField="CurrencyValue" Visible="True" HeaderText="Price" DataFormatString="{0:c}"> <ItemStyle HorizontalAlign="Right"> </ItemStyle> </asp:BoundColumn> <asp:TemplateColumn HeaderText="Select Item" Visible="True" > <ItemTemplate> <asp:CheckBox id="SelectCheckBox" Text="Add to Cart" Checked="False" runat="server"/> </ItemTemplate> </asp:TemplateColumn> </Columns> </asp:DataGrid> <br /><br /> <asp:Button id="SubmitButton" Text="Submit" OnClick = "Button_Click" runat="server"/> <br /><br /> <asp:Label id="Message" runat="server"/> <hr /> <asp:CheckBox id="ShowCheckBox" Text="Show first column" AutoPostBack="True" OnCheckedChanged="Check_Change" Checked="True" runat="server"/> </form> </body> </html>
Available since 1.1
