title: how to return all values when textbox is empty
body: <p>I have a textbox [DepartureRunwayTextBox] binding with one column [DepartureRunway]. I want to retrieve all values in GridView if the textbox is empty. I set ConvertEmptyStringToNull to false and tried CancelSelectOnNullParameter on true and false, and it doesn't work the way that I want. Please let me know how can I fix this.</p>
  
  <p><strong>Aspx</strong></p>
  
  <pre><code>&lt;asp:Label ID="DepartureRunwayLabel" runat="server" Text="Departure Runway" Font-Size="Medium"&gt;&lt;/asp:Label&gt;&amp;nbsp;
  &lt;asp:TextBox ID="DepartureRunwayTextBox" runat="server" Font-Size="Medium"&gt;&lt;/asp:TextBox&gt;
  
  &lt;asp:SqlDataSource ID="DepartureRunwaySqlDataSource" runat="server" ConnectionString="&lt;%$ ConnectionStrings:ConnectionString %&gt;" SelectCommand="SELECT [Departure Runway] AS Departure_Runway FROM [Movement]" CancelSelectOnNullParameter="True"&gt;&lt;/asp:SqlDataSource&gt;
  
  
      ...
  
  &lt;asp:Panel ID="GridViewPanel" runat="server"&gt;
              &lt;asp:GridView ID="GridView" runat="server" AllowPaging="True" AllowSorting="True" AutoGenerateColumns="False" DataKeyNames="AircraftID" DataSourceID="GridViewDataSource" BackColor="White" BorderColor="#DEDFDE" BorderStyle="None" BorderWidth="1px" CellPadding="4" ForeColor="Black" GridLines="Vertical" OnSelectedIndexChanged="GridView_SelectedIndexChanged" EnableSortingAndPagingCallbacks="True" ShowFooter="True" Visible="False"&gt;
                  &lt;AlternatingRowStyle BackColor="White" /&gt;
                  &lt;Columns&gt;
      ...
  </code></pre>
  
  <p><strong>Aspx.cs</strong></p>
  
  <pre><code>using System;
  using System.Collections.Generic;
  using System.Linq;
  using System.Web;
  using System.Web.UI;
  using System.Web.UI.WebControls;
  
  namespace ATOMS2._0
  {
      public partial class _Default : Page
      {
          protected void Page_Load(object sender, EventArgs e)
          {
  
          }
  
          protected void Search_Click(object sender, EventArgs e)
          {
              GridView.Visible = true;
          }
  
          protected void GridView_SelectedIndexChanged(object sender, EventArgs e)
          {
  
          }
      }
  }
  </code></pre>