In this example we are going to describe how to implement CheckAll CheckBox in GridView to check all the rows in gridView.For this we have put a checkBox in header Template of gridview which on checking will check all the rows in gridview using server side code.

<asp:GridView ID="GridView1" runat="server"
DataSourceID="SqlDataSource1"
AutoGenerateColumns="false"
CellPadding="2" ForeColor="#333333"
GridLines="Both"
DataKeyNames="ID"
OnRowDataBound="GridView1_RowDataBound">
<Columns>
<asp:TemplateField HeaderText="CheckAll">
<HeaderTemplate>
<asp:CheckBox ID="chkSelectAll" runat="server"
AutoPostBack="true"
OnCheckedChanged="chkSelectAll_CheckedChanged"/>
</HeaderTemplate>
<ItemTemplate>
<asp:CheckBox ID="chkSelect" runat="server"
AutoPostBack="true"
OnCheckedChanged="chkSelect_CheckedChanged"/>
</ItemTemplate>
</asp:TemplateField>
<asp:BoundField DataField="ID" HeaderText="ID"
SortExpression="ID"/>
<asp:TemplateField HeaderText="Name" SortExpression="Name">
<ItemTemplate>
<asp:TextBox ID="txtName" runat="server"
Text='<%# Bind("Name") %>' ForeColor="Blue"
BorderStyle="none" BorderWidth="0px"
ReadOnly="true" >
</asp:TextBox>
</ItemTemplate>
</asp:TemplateField>
</Columns>
</asp:GridView>
<asp:SqlDataSource ID="SqlDataSource1" runat="server"
ConnectionString="<%$ ConnectionStrings:ConnectionString %>"
SelectCommand="SELECT [ID], [Name], [Location] FROM [Details]"
DeleteCommand="DELETE FROM Details WHERE (ID = @ID)"
UpdateCommand="UPDATE [Details] SET [Name] = @Name,
[Location] = @Location WHERE [ID] = @ID">
<DeleteParameters>
<asp:Parameter Name="ID" />
</DeleteParameters>
<UpdateParameters>
<asp:Parameter Name="Name" />
<asp:Parameter Name="Location" />
<asp:Parameter Name="ID" />
</UpdateParameters>
</asp:SqlDataSource>
<asp:Button ID="btnUpdate" runat="server"
OnClick="btnUpdate_Click" Text="Update" />
<asp:Button ID="btnDelete" runat="server"
OnClick="btnDelete_Click"
Text="Delete" />

protected void chkSelectAll_ CheckedChanged(object sender,EventArgs e)
{
CheckBox chkAll =
(CheckBox)GridView1.HeaderRow.FindControl("chkSelectAll");
if (chkAll.Checked == true)
{
foreach (GridViewRow gvRow in GridView1.Rows)
{
CheckBox chkSel =
(CheckBox)gvRow.FindControl("chkSelect");
chkSel.Checked = true;
TextBox txtname = (TextBox)gvRow.FindControl("txtName");
TextBox txtlocation = (TextBox)gvRow.FindControl("txtLocation");
txtname.ReadOnly = false;
txtlocation.ReadOnly = false;
txtname.ForeColor = System.Drawing.Color.Black;
txtlocation.ForeColor = System.Drawing.Color.Black;
}
}
else
{
foreach (GridViewRow gvRow in GridView1.Rows)
{
CheckBox chkSel = (CheckBox)gvRow.FindControl("chkSelect");
chkSel.Checked = false;
TextBox txtname = (TextBox)gvRow.FindControl("txtName");
TextBox txtlocation = (TextBox)gvRow.FindControl("txtLocation");
txtlocation.ReadOnly = true;
txtname.ForeColor = System.Drawing.Color.Blue;
txtlocation.ForeColor = System.Drawing.Color.Blue;
}
}
}

Download sample code attached