GridView.AllowSorting Property
Definition
Important
Some information relates to prerelease product that may be substantially modified before it’s released. Microsoft makes no warranties, express or implied, with respect to the information provided here.
Gets or sets a value indicating whether the sorting feature is enabled.
public:
virtual property bool AllowSorting { bool get(); void set(bool value); };public virtual bool AllowSorting { get; set; }member this.AllowSorting : bool with get, setPublic Overridable Property AllowSorting As BooleanProperty Value
true if the sorting feature is enabled; otherwise, false. The default is false.
Examples
The following example demonstrates how to use the AllowSorting property to enable sorting in a GridView control when automatically generated columns are used.
<%@ Page language="C#" %>
<!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" >
<head runat="server">
<title>GridView AllowSorting Example</title>
</head>
<body>
<form id="form1" runat="server">
<h3>GridView AllowSorting Example</h3>
<asp:gridview id="CustomersGridView"
datasourceid="CustomersSource"
autogeneratecolumns="true"
emptydatatext="No data available."
allowsorting="true"
runat="server">
</asp:gridview>
<!-- This example uses Microsoft SQL Server and connects -->
<!-- to the Northwind sample database. Use an ASP.NET -->
<!-- expression to retrieve the connection string value -->
<!-- from the Web.config file. -->
<asp:sqldatasource id="CustomersSource"
selectcommand="Select [CustomerID], [CompanyName], [Address], [City], [PostalCode], [Country] From [Customers]"
connectionstring="<%$ ConnectionStrings:NorthWindConnectionString%>"
runat="server"/>
</form>
</body>
</html>
<%@ Page language="VB" %>
<!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" >
<head runat="server">
<title>GridView AllowSorting Example</title>
</head>
<body>
<form id="form1" runat="server">
<h3>GridView AllowSorting Example</h3>
<asp:gridview id="CustomersGridView"
datasourceid="CustomersSource"
autogeneratecolumns="true"
emptydatatext="No data available."
allowsorting="true"
runat="server">
</asp:gridview>
<!-- This example uses Microsoft SQL Server and connects -->
<!-- to the Northwind sample database. Use an ASP.NET -->
<!-- expression to retrieve the connection string value -->
<!-- from the Web.config file. -->
<asp:sqldatasource id="CustomersSource"
selectcommand="Select [CustomerID], [CompanyName], [Address], [City], [PostalCode], [Country] From [Customers]"
connectionstring="<%$ ConnectionStrings:NorthWindConnectionString%>"
runat="server"/>
</form>
</body>
</html>
The following example demonstrates how to use the AllowSorting property to enable sorting in a GridView control when a Columns collection is defined. An image is also programmatically added to the header of the column being sorted to indicate the sort direction. You must provide your own images for this sample to work.
<%@ Page language="C#" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<script runat="server">
void CustomersGridView_RowCreated(Object sender, GridViewRowEventArgs e)
{
// Use the RowType property to determine whether the
// row being created is the header row.
if (e.Row.RowType == DataControlRowType.Header)
{
// Call the GetSortColumnIndex helper method to determine
// the index of the column being sorted.
int sortColumnIndex = GetSortColumnIndex();
if (sortColumnIndex != -1)
{
// Call the AddSortImage helper method to add
// a sort direction image to the appropriate
// column header.
AddSortImage(sortColumnIndex, e.Row);
}
}
}
// This is a helper method used to determine the index of the
// column being sorted. If no column is being sorted, -1 is returned.
int GetSortColumnIndex()
{
// Iterate through the Columns collection to determine the index
// of the column being sorted.
foreach (DataControlField field in CustomersGridView.Columns)
{
if (field.SortExpression == CustomersGridView.SortExpression)
{
return CustomersGridView.Columns.IndexOf(field);
}
}
return -1;
}
// This is a helper method used to add a sort direction
// image to the header of the column being sorted.
void AddSortImage(int columnIndex, GridViewRow headerRow)
{
// Create the sorting image based on the sort direction.
Image sortImage = new Image();
if (CustomersGridView.SortDirection == SortDirection.Ascending)
{
sortImage.ImageUrl = "~/Images/Ascending.jpg";
sortImage.AlternateText = "Ascending Order";
}
else
{
sortImage.ImageUrl = "~/Images/Descending.jpg";
sortImage.AlternateText = "Descending Order";
}
// Add the image to the appropriate header cell.
headerRow.Cells[columnIndex].Controls.Add(sortImage);
}
</script>
<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
<title>GridView AllowSorting Example</title>
</head>
<body>
<form id="form1" runat="server">
<h3>GridView AllowSorting Example</h3>
<asp:gridview id="CustomersGridView"
datasourceid="CustomersSource"
autogeneratecolumns="false"
emptydatatext="No data available."
allowsorting="true"
onrowcreated="CustomersGridView_RowCreated"
runat="server">
<columns>
<asp:boundfield datafield="CustomerID"
headertext="Customer ID"
headerstyle-wrap="false"
sortexpression="CustomerID"/>
<asp:boundfield datafield="CompanyName"
headertext="CompanyName"
headerstyle-wrap="false"
sortexpression="CompanyName"/>
<asp:boundfield datafield="Address"
headertext="Address"
headerstyle-wrap="false"
sortexpression="Address"/>
<asp:boundfield datafield="City"
headertext="City"
headerstyle-wrap="false"
sortexpression="City"/>
<asp:boundfield datafield="PostalCode"
headertext="Postal Code"
headerstyle-wrap="false"
sortexpression="PostalCode" />
<asp:boundfield datafield="Country"
headertext="Country"
headerstyle-wrap="false"
sortexpression="Country"/>
</columns>
</asp:gridview>
<!-- This example uses Microsoft SQL Server and connects -->
<!-- to the Northwind sample database. Use an ASP.NET -->
<!-- expression to retrieve the connection string value -->
<!-- from the Web.config file. -->
<asp:sqldatasource id="CustomersSource"
selectcommand="Select [CustomerID], [CompanyName], [Address], [City], [PostalCode], [Country] From [Customers]"
connectionstring="<%$ ConnectionStrings:NorthWindConnectionString%>"
runat="server"/>
</form>
</body>
</html>
<%@ Page language="VB" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<script runat="server">
Sub CustomersGridView_RowCreated(ByVal sender As Object, ByVal e As GridViewRowEventArgs)
' Use the RowType property to determine whether the
' row being created is the header row.
If e.Row.RowType = DataControlRowType.Header Then
' Call the GetSortColumnIndex helper method to determine
' the index of the column being sorted.
Dim sortColumnIndex As Integer = GetSortColumnIndex()
If sortColumnIndex <> -1 Then
' Call the AddSortImage helper method to add
' a sort direction image to the appropriate
' column header.
AddSortImage(sortColumnIndex, e.Row)
End If
End If
End Sub
' This is a helper method used to determine the index of the
' column being sorted. If no column is being sorted, -1 is returned.
Function GetSortColumnIndex() As Integer
' Iterate through the Columns collection to determine the index
' of the column being sorted.
Dim field As DataControlField
For Each field In CustomersGridView.Columns
If field.SortExpression = CustomersGridView.SortExpression Then
Return CustomersGridView.Columns.IndexOf(field)
End If
Next
Return -1
End Function
' This is a helper method used to add a sort direction
' image to the header of the column being sorted.
Sub AddSortImage(ByVal columnIndex As Integer, ByVal row As GridViewRow)
' Create the sorting image based on the sort direction.
Dim sortImage As New Image()
If CustomersGridView.SortDirection = SortDirection.Ascending Then
sortImage.ImageUrl = "~/Images/Ascending.jpg"
sortImage.AlternateText = "Ascending Order"
Else
sortImage.ImageUrl = "~/Images/Descending.jpg"
sortImage.AlternateText = "Descending Order"
End If
' Add the image to the appropriate header cell.
row.Cells(columnIndex).Controls.Add(sortImage)
End Sub
</script>
<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
<title>GridView AllowSorting Example</title>
</head>
<body>
<form id="form1" runat="server">
<h3>GridView AllowSorting Example</h3>
<asp:gridview id="CustomersGridView"
datasourceid="CustomersSource"
autogeneratecolumns="false"
emptydatatext="No data available."
allowsorting="true"
onrowcreated="CustomersGridView_RowCreated"
runat="server">
<columns>
<asp:boundfield datafield="CustomerID"
headertext="Customer ID"
headerstyle-wrap="false"
sortexpression="CustomerID"/>
<asp:boundfield datafield="CompanyName"
headertext="CompanyName"
headerstyle-wrap="false"
sortexpression="CompanyName"/>
<asp:boundfield datafield="Address"
headertext="Address"
headerstyle-wrap="false"
sortexpression="Address"/>
<asp:boundfield datafield="City"
headertext="City"
headerstyle-wrap="false"
sortexpression="City"/>
<asp:boundfield datafield="PostalCode"
headertext="Postal Code"
headerstyle-wrap="false"
sortexpression="PostalCode" />
<asp:boundfield datafield="Country"
headertext="Country"
headerstyle-wrap="false"
sortexpression="Country"/>
</columns>
</asp:gridview>
<!-- This example uses Microsoft SQL Server and connects -->
<!-- to the Northwind sample database. Use an ASP.NET -->
<!-- expression to retrieve the connection string value -->
<!-- from the Web.config file. -->
<asp:sqldatasource id="CustomersSource"
selectcommand="Select [CustomerID], [CompanyName], [Address], [City], [PostalCode], [Country] From [Customers]"
connectionstring="<%$ ConnectionStrings:NorthWindConnectionString%>"
runat="server"/>
</form>
</body>
</html>
Remarks
When a data source control that supports sorting is bound to the GridView control, the GridView control can take advantage of the data source control's capabilities and provide automatic sorting functionality. When the GridView control is bound to a data source by setting the DataSource property programmatically, you must provide the sorting functionality by using the Sorting event.
Note
Different data sources have different requirements for enabling their sorting capabilities. To determine the requirements, see the documentation for the specific data source.
To enable sorting, set the AllowSorting property to true. When sorting is enabled, the heading text for each column field with its SortExpression property set is displayed as a link button.
Note
The SortExpression property for an automatically generated columns field is automatically populated. If you define your own columns through the Columns collection, you must set the SortExpression property for each column; otherwise, the column will not display the link button in the header.
Clicking the link button for a column causes the items in the GridView control to be sorted based on the sort expression. Typically, the sort expression is simply the name of the field displayed in the column, which causes the GridView control to sort with respect to that column. To sort by multiple fields, use a sort expression that contains a comma-separated list of field names. You can determine the sort expression that the GridView control is applying by using the SortExpression property. Clicking a column's link button repeatedly toggles the sort direction between ascending and descending order. To determine the current sort direction, use the SortDirection property.
The GridView control provides several events that you can use to perform a custom action when sorting occurs. The following table lists the available events.
| Event | Description |
|---|---|
| Sorted | Occurs when the hyperlink to sort a column is clicked, but after the GridView control handles the sort operation. This event is commonly used to perform a task after the user clicks a hyperlink to sort a column. |
| Sorting | Occurs when the hyperlink to sort a column is clicked, but before the GridView control handles the sort operation. This event is often used to cancel the sorting operation or to perform a custom sorting routine. |
