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How To Show All Items Using a DropDownList and a GridView Control in ASP.NET 2.0 with VS2005

Updated: at 11:17 PM

We often want to have a gridview which selects items based on a dropdownlist. It's trivial to do this in the VS2005 designer by simply first creating an SqlDataSource with a where clause, then with the sqldatasource wizard, assign the SelectedValue of the dropdownlist to the GridView.

The application running looks like this:

And the page source to do is simply this:

<%@ Page Language=”C#” %>

<!DOCTYPE html PUBLIC-//W3C//DTD XHTML 1.0 Transitional//EN” “>

<script runat=”server> </script>

<html xmlns=”> <head runat=”server> <title>Simple GridView With DropDownList Selection</title> </head> <body> <form id=”form1? runat=”server> <div> <asp:DropDownList ID=”DropDownList1? runat=”serverAutoPostBack=”True> <asp:ListItem>Ikura</asp:ListItem> <asp:ListItem>Konbu</asp:ListItem> </asp:DropDownList><br /> <asp:SqlDataSource ID=”SqlDataSource1? runat=”serverConnectionString=”&lt;%$ ConnectionStrings:NorthWindConnectionString %&gt;“ SelectCommand=”SELECT [ProductName], [UnitsInStock], [UnitsOnOrder] FROM [Alphabetical List of Products] WHERE ([ProductName] = @ProductName2)”> <SelectParameters> <asp:ControlParameter ControlID=”DropDownList1? Name=”ProductName2? PropertyName=”SelectedValueType=”String/> </SelectParameters> </asp:SqlDataSource> <asp:GridView ID=”GridView1? runat=”serverAutoGenerateColumns=”FalseDataSourceID=”SqlDataSource1?> <Columns> <asp:BoundField DataField=”ProductNameHeaderText=”ProductNameSortExpression=”ProductName/> <asp:BoundField DataField=”UnitsInStockHeaderText=”UnitsInStockSortExpression=”UnitsInStock/> <asp:BoundField DataField=”UnitsOnOrderHeaderText=”UnitsOnOrderSortExpression=”UnitsOnOrder/> </Columns> </asp:GridView> </div> </form> </body> </html>

However, what if you want to have a show all option in your DropDownList? My suggestion is to abandon (somewhat) the visual programming model (or at least that's the only way I can think of doing it) and add the SelectParameters in the Page_Load event of the page. In addition, to get all the rows to show, I suggest adding the Sql Injection trick which is add an OR to the sql. You can that make the OR always return true, or always return false. I do this by simply passing a 1=@CompareInteger to the Sql that always gets evaluated. Then dynamically set the CompareInteger to 1 or 999. 1 makes all the rows return, 999 forces the evaluation of the ProductName=@ProductName part of the Where clause.

Here is what the application looks like running:

And here is the code that actually does the job.

<%@ Page Language="C#" %>

<!DOCTYPE html PUBLIC ”-//W3C//DTD XHTML 1.0 Transitional//EN”>

<script runat=“server”>

<span class="kwrd">protected</span> <span class="kwrd">void</span> Page_Load(<span class="kwrd">object</span> sender, EventArgs e)

    <span class="kwrd">if</span> (!IsPostBack)
        ControlParameter cp =
            <span class="kwrd">new</span> ControlParameter(<span class="str">&quot;ProductName&quot;</span>,TypeCode.String,<span class="str">&quot;DropDownList1&quot;</span>,<span class="str">&quot;SelectedValue&quot;</span>);

        Parameter p = <span class="kwrd">new</span> Parameter(<span class="str">&quot;CompareInteger&quot;</span>, TypeCode.Int32);
        p.DefaultValue = <span class="str">&quot;1&quot;</span>;

<span class="kwrd">protected</span> <span class="kwrd">void</span> DropDownList1_SelectedIndexChanged(<span class="kwrd">object</span> sender, EventArgs e)
    <span class="kwrd">if</span> (DropDownList1.SelectedValue.Equals(<span class="str">&quot;(All)&quot;</span>))
        SqlDataSource1.SelectParameters[1].DefaultValue = <span class="str">&quot;1&quot;</span>;
    <span class="kwrd">else</span>
        SqlDataSource1.SelectParameters[1].DefaultValue = <span class="str">&quot;999&quot;</span>;  <span class="rem">// not one</span>


<html xmlns=“ > <head runat=“server”> <title>DropDownList and GridView with Show All Option</title> </head> <body> <form id=“form1” runat=“server”> <div> <asp:DropDownList ID=“DropDownList1” runat=“server” AutoPostBack=“True” OnSelectedIndexChanged=“DropDownList1_SelectedIndexChanged”> <asp:ListItem Value=“(All)”></asp:ListItem> <asp:ListItem>Ikura</asp:ListItem> <asp: pan style=“color: maroon;“>ListItem>Konbu</asp:ListItem> </asp:DropDownList><br /> <br /> <asp:GridView ID=“GridView1” runat=“server” AutoGenerateColumns=“False” DataSourceID=“SqlDataSource1”> <Columns> <asp:BoundField DataField=“ProductName” HeaderText=“ProductName” SortExpression=“ProductName” /> <asp:BoundField DataField=“UnitsInStock” HeaderText=“UnitsInStock” SortExpression=“UnitsInStock” /> </Columns> </asp:GridView> <br /> <asp:SqlDataSource ID=“SqlDataSource1” runat=“server” ConnectionString=”<%$ ConnectionStrings:NorthWindConnectionString %>” SelectCommand=“SELECT [ProductName], [UnitsInStock] FROM [Alphabetical List of Products] WHERE ([ProductName] = @ProductName OR 1 = @CompareInteger) ORDER BY [ProductName]”> </asp:SqlDataSource> </div> </form> </body> </html>

Notice that autopostback is set on the dropdownlist as well as the select change event. That's it! Give it a try.