Question

I have a gridview which I want to sort when any of its column header is clicked. There is a DataTable that is built on runtime and assigned to the gridview to populate data. Here is the DataTable and Gridview:

DataTable dtMedication = new DataTable();
dtClientMedications.Columns.Add("Id");
dtClientMedications.Columns.Add("BrandName");
dtClientMedications.Columns.Add("GenericName");
dtClientMedications.Columns.Add("Dosage");
dtClientMedications.Columns.Add("Physician");
dtClientMedications.Columns.Add("DatePrescribed");
dtClientMedications.Columns.Add("Status");
dtClientMedications.Columns.Add("ClientMedicationDataId");

<asp:GridView ID="gdvMainList" runat="server" AutoGenerateColumns="False"
                            SkinID="PagedGridView" onrowcommand="gdvMainList_RowCommand" 
                            DataKeyNames="Id" onsorting="gdvMainList_Sorting">
                            <PagerStyle CssClass="gridpager" HorizontalAlign="Right" />
                            <Columns>
                                <ucc:CommandFieldControl HeaderText="Actions" ShowDeleteButton="true" ButtonType="Image"
                                    DeleteImageUrl="~/App_Themes/Default/images/delete.png" ShowEditButton="true"
                                    EditImageUrl="~/App_Themes/Default/images/edit.png" DeleteConfirmationText="Are you sure you want to delete?">
                                    <ItemStyle HorizontalAlign="Center" Width="60px" />
                                </ucc:CommandFieldControl>
                                <asp:BoundField DataField="BrandName" HeaderText="Brand Name" />
                                <asp:BoundField DataField="GenericName" HeaderText="Generic Name" />
                                <asp:BoundField DataField="Dosage" HeaderText="Dosage" />
                                <asp:BoundField DataField="Physician" HeaderText="Physician" />
                                <asp:BoundField DataField="DatePrescribed" HeaderText="Date Prescribed" />
                                <asp:BoundField DataField="Status" HeaderText="Status" />
                                <asp:TemplateField HeaderText="">
                                    <ItemStyle CssClass="HiddenCol" Width="0px" />
                                    <HeaderStyle CssClass="HiddenCol" />
                                    <ItemTemplate>
                                        <asp:HiddenField ID="hdfClientMedicationDataId" runat="server" Value='<%#Bind("ClientMedicationDataId") %>' />
                                    </ItemTemplate>
                                </asp:TemplateField>
                            </Columns>
                            <EmptyDataTemplate>
                                <div class="divEmptyGrid">
                                    --- No Medication Exists ---
                                </div>
                            </EmptyDataTemplate>
                        </asp:GridView>

Answer 1

First step to set AllowSorting property of GridView to true then add SortExpression property for each column you would to use for sorting:

SortExpression property indicates the expression that should be
used to sort the data when that field’s sorting header link is clicked

Let’s consider BoundField from your code above, I have added a SortExpression property with value set to BrandName which means that when the column header for BrandName will be clicked column ‘BrandName’ in your DataTable will be used to sort the data:

Now in gdvMainList_Sorting event you have to rebind the grid to sorted data:

protected void gdvMainList_Sorting(object sender, System.Web.UI.WebControls.GridViewSortEventArgs e)
{
    //Using DataView for sorting DataTable's data
    DataView view = dtMedication.DefaultView;
    view.Sort = String.Format("{0} {1}", e.SortExpression, GetSortingDirection());
    gdvMainList.DataSource = view;
    gdvMainList.DataBind();
}

If you have noticed I have used getSortingDirection(), which a method that returns either ‘ASC’ or ‘DESC’ for sorting data in either ascending or descending order, respectively.

protected string GetSortingDirection() 
{
    if(ViewState["SortDirection"] == null)
        ViewState["SortDirection"] = "ASC";
    else if(ViewState["SortDirection"] == "ASC")
        ViewState["SortDirection"] = "DESC";
    else
        ViewState["SortDirection"] = "ASC";

    return ViewState["SortDirection"];
}

Some useful links:

1. GridView sorting using VB.net
2. Sorting and Paging tutorial