automatically generating content in a dropdown list based on the selection of another dropdown list


 i currently have a "categories" dropdown list i'm using to help filter data in a datagrid (have it setup using data and table adapters).

 i've introduced another dropdown list (called subcategories) to filter the datagrid so it only displays records that fit in both the category and subcategories.

it all works fine, but i'm wanting to set it so the subcategories dropdown list gets generated on the client-side depending on the category selected.

 does anybody have any quick tutorials or a quick explination on how i could do this? am i missing something simple like having to set a relationship between the two adapters?


thanks in advance

10/31/2006 4:43:57 AM 93655 articles. 6 followers. Follow

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Suppose you have two DDL: ddl1 and ddl2, when you select from ddl1, you want to filter ddl2 ok?

<asp:DropDownList Id="ddl1" OnChange="FilterDDL('ddl1', 'ddl2');" ....></asp:DropDownList>

The above is the decleration of the first DDL. The second DDL is simple, just a normal DDL.

When the page loads, you populate both DDLs!

Now, the FilterDDL will be a JavaScript method as follows:

<%@ Page language="c#" Codebehind="WebForm1.aspx.cs" AutoEventWireup="false" Inherits="Testing.Bilal.WebForm1" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" >
			function FilterDDL(source, target) 
				var ddlSource = document.getElementById(source);
				var ddlTarget = document.getElementById(target);

				// Get selected item in the source ddl
				var selectedVal;
				selectedVal = ddlSource.options[ddlSource.options.selectedIndex].text;
				if ((ddlSource != null) && (ddlTarget != null)) 
					var index;
					for(index=0; index<ddlTarget.options.length;index++)
						// if the selected value in source is equal to an item in the target ddl, remove it
						if (selectedVal == ddlTarget.options[index].value)
							ddlTarget.remove(index); // remove based on index
		<form id="Form1" method="post" runat="server">
				<asp:DropDownList id="ddl1" runat="server" OnChange="FilterDDL('ddl1', 'ddl2');">
					<asp:ListItem Value="c#">c#</asp:ListItem>
					<asp:ListItem Value=""></asp:ListItem>
					<asp:ListItem Value=""></asp:ListItem>
				<asp:DropDownList id="ddl2" runat="server">
					<asp:ListItem Value="cobol">cobol</asp:ListItem>
					<asp:ListItem Value=""></asp:ListItem>
					<asp:ListItem Value="delphi">delphi</asp:ListItem>

 That was a sample page, that shows two DDLs, the idea is when you select a value from first ddl, the second DDL will be filtered in a sense, any value thatit contains that was selected in the first ddl, it will be removed.

The idea is just to show you how you control the DDL elements not more. So you have access for each option inside the DDL and for the text+value.

Use this code to customize it for your needs, hope this helps!


Bilal Hadiar, MCP, MCTS, MCPD, MCT
Microsoft MVP - Telerik MVP
10/31/2006 5:30:53 AM
If you've went thru the quickstart, you will find a good example using script callback There (to the buttom of page and see). Also, ajax's UpdatePanel will make this cascading dropdown quite a simple job.
你好! Just FYI o_O
10/31/2006 7:20:17 AM

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