protected void GridView1_PageIndexChanging(object sender, GridViewPageEventArgs e)
{
    GridView1.DataSource = SortDataTable(GetYourDataSource(), true);
    GridView1.PageIndex = e.NewPageIndex;
    GridView1.DataBind();
}
   
private string GridViewSortDirection
{
    get { return ViewState["SortDirection"] as string ?? "ASC"; }
    set { ViewState["SortDirection"] = value; }
}

private string GridViewSortExpression
{
    get { return ViewState["SortExpression"] as string ?? string.Empty; }
    set { ViewState["SortExpression"] = value; }
}

private string ToggleSortDirection()
{
    switch (GridViewSortDirection)
    {
        case "ASC":
            GridViewSortDirection = "DESC";
            break;
        case "DESC":
            GridViewSortDirection = "ASC";
            break;
    }
    return GridViewSortDirection;
}

protected DataView SortDataTable(DataTable dataTable, bool isPageIndexChanging)
{
    if (dataTable != null)
    {
        DataView dataView = new DataView(dataTable);
        if (GridViewSortExpression != string.Empty)
        {
            if (isPageIndexChanging)
            {
                dataView.Sort = string.Format("{0} {1}", 
                              GridViewSortExpression,GridViewSortDirection);
            }
            else
            {
                dataView.Sort = string.Format("{0} {1}",
                              GridViewSortExpression,ToggleSortDirection());
            }
        }
    return dataView;
    }
    else
    {
        return new DataView();
    }
}

protected void GridView1_Sorting(object sender, GridViewSortEventArgs e)
{
    GridViewSortExpression = e.SortExpression;
    int pageIndex = GridView1.PageIndex;
    GridView1.DataSource = SortDataTable(GetYourDataSource(), false);
    GridView1.DataBind();
    GridView1.PageIndex = pageIndex;
}

Related posts:

Dynamically sort in the GridView control

How to sort and page in the GridView control

When there is no data for the GridView control to display, by default the control is not rendered. If you want to show headers even if there is no data, you can create a temporary DataTable object that contains an empty record and then bind the GridView control to the data table in the page's Init event. The following example shows how to do this.

protected void GridView1_Init(Object sender, EventArgs e)
{
    DataTable dt = new DataTable();
    dt.Columns.Add("Column1");
    dt.Columns.Add("Column2");
    DataRow dr = dt.NewRow();
    dr["Column1"] = "";
    dr["Column2"] = "";
    dt.Rows.Add(dr);
    GridView1.DataSource = dt;
    GridView1.DataBind();
}

public class EmptyGridView : GridView
{
    #region Properties
    /// <summary>
    /// Enable or Disable generating an empty table if no data rows in source
    /// </summary>
    [
    Description("Enable or disable generating an empty table with headers 
         when no data rows are available in the data source."),
    Category("Misc"),
    DefaultValue("true"),
    ]
    public bool ShowEmptyTable
    {
        get
        {
            object o = ViewState["ShowEmptyTable"];
            return (o != null ? (bool)o : true);
        }
        set
        {
            ViewState["ShowEmptyTable"] = value;
        }
    }
    /// <summary>
    /// Get or Set Text to display in empty data row
    /// </summary>
    [
    Description("Text to display in the empty data row."),
    Category("Misc"),
    DefaultValue(""),
    ]
    public string EmptyTableRowText
    {
        get
        {
            object o = ViewState["EmptyTableRowText"];
            return (o != null ? o.ToString() : "");
        }
        set
        {
            ViewState["EmptyTableRowText"] = value;
        }
    }
    #endregion
    protected override int CreateChildControls(System.Collections.IEnumerable 
            dataSource, bool dataBinding)
    {
        int numRows = base.CreateChildControls(dataSource, dataBinding);
        // No data rows created, so create an empty table if enabled.
        if (numRows == 0 && ShowEmptyTable)
        {
            //create table
            Table table = new Table();
            table.ID = this.ID;
            //create a new header row
            GridViewRow row = base.CreateRow(-1, -1, DataControlRowType.Header, 
                DataControlRowState.Normal);
            //convert the exisiting columns into an array and initialize
            DataControlField[] fields = new 
                DataControlField[this.Columns.Count];
            this.Columns.CopyTo(fields, 0);
            this.InitializeRow(row, fields);
            table.Rows.Add(row);
            //create the empty row
            row = new GridViewRow(-1, -1, DataControlRowType.DataRow,
               DataControlRowState.Normal);
            TableCell cell = new TableCell();
            cell.ColumnSpan = this.Columns.Count;
            cell.Width = Unit.Percentage(100);
            cell.Controls.Add(new LiteralControl(EmptyTableRowText));
            row.Cells.Add(cell);
            table.Rows.Add(row);
            this.Controls.Add(table);
        }
        return numRows;
    }
}

How to display a Gridview header and footer when the SqlDataSource control returns no data

1.3 Size of GridView overflows [Top]

If the GridView control attempts to display more columns or rows than there is space available in the page, this can cause the GridView control to overflow and alter the appearance of the whole page. You can resolve this by adding a horizontal or vertical scroll bar to the control, as shown in the following example:

<div style="vertical-align:top; height:200px; width:100%; overflow:auto;">