How to delete Multiple rows in Data Gridview control

<asp:SqlDataSource ID="SqlDataSource1" Runat="server"
    SelectCommand="SELECT EmployeeID, LastName, City FROM Employees"
    DeleteCommand="DELETE FROM Employees WHERE [EmployeeID] = @EmployeeID"
    ConnectionString="<%$ ConnectionStrings:NorthwindConnectionString %>" >

    <DeleteParameters>
        <asp:Parameter Name="EmployeeID" />
    </DeleteParameters>
</asp:SqlDataSource>

<asp:TemplateField>
    <ItemTemplate>
        <asp:CheckBox ID="chkRows" runat="server"/>
    </ItemTemplate>
</asp:TemplateField>

<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" DataKeyNames="EmployeeID" DataSourceID="SqlDataSource1">
    <Columns>
        <asp:TemplateField>
            <ItemTemplate>
                <asp:CheckBox ID="cbRows" runat="server"/>
            </ItemTemplate>
        </asp:TemplateField>
        <asp:BoundField DataField="EmployeeID" HeaderText="EmployeeID" InsertVisible="False" ReadOnly="True" SortExpression="EmployeeID" />
        <asp:BoundField DataField="LastName" HeaderText="LastName" SortExpression="LastName" />
        <asp:BoundField DataField="City" HeaderText="City" SortExpression="City" />
    </Columns>
</asp:GridView>

<asp:SqlDataSource ID="SqlDataSource1" Runat="server"
    SelectCommand="SELECT EmployeeID, LastName, City FROM Employees"
    DeleteCommand="DELETE FROM Employees WHERE [EmployeeID] = @EmployeeID"
    ConnectionString="<%$ ConnectionStrings:NorthwindConnectionString %>" >

    <DeleteParameters>
        <asp:Parameter Name="EmployeeID" />
    </DeleteParameters>
</asp:SqlDataSource>

<asp:Button ID="btnMultipleRowDelete"  OnClick="btnMultipleRowDelete_Click" runat="server"  Text="Delete Rows" />

protected void btnMultipleRowDelete_Click(object sender, EventArgs e)
{
    // Looping through all the rows in the GridView
    foreach (GridViewRow row in GridView1.Rows)
    {
        CheckBox checkbox = (CheckBox)row.FindControl("cbRows");

        //Check if the checkbox is checked.
        //value in the HtmlInputCheckBox's Value property is set as the

        //value of the delete command's parameter.
        if (checkbox.Checked)
        {
            // Retreive the Employee ID
            int employeeID = Convert.ToInt32(GridView1.DataKeys[row.RowIndex].Value);

            // Pass the value of the selected Employye ID to the Delete //command.
            SqlDataSource1.DeleteParameters["EmployeeID"].DefaultValue = employeeID.ToString();
            SqlDataSource1.Delete();
        }
    }
}