ASP.NET C# Dropdown List using User Control

Question

First, I am new to ASP.NET

In order to reuse my dropdown list across different forms on different pages, I was advised that to use User Control to accomplish this. So I did some reading about user control and attempted to play around with it, but couldn't get it work since I am new to ASP.NET. Get this error:

Cannot access a non-static member of outer type 'ASP.Vendor' via nested type 'ASP.Vendor._Default'

1) I create a Controls\Vendor.ascx file

<% @ Control Language="C#" ClassName="Vendor" %>
<%@ Import Namespace="System.Data" %>
<%@ Import Namespace="System.Data.SqlClient" %>
<%@ Import Namespace="System.Web.UI" %>
<%@ Import Namespace="System.Web.UI.WebControls" %>
<%@ Import Namespace="System.Configuration" %>
<%@ Import Namespace="System.Linq" %>
<%@ Import Namespace="System.Collections.Generic" %>

<script runat="server">

public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            FillVendor();
        }
    }


    private void FillVendor()
    {
        string strConn = ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString;
       System.Data.SqlClient.SqlConnection conn = new System.Data.SqlClient.SqlConnection(strConn);
        SqlCommand cmd = new SqlCommand();
        cmd.Connection = conn;
        cmd.CommandType = CommandType.Text;
        cmd.CommandText = "SELECT VendorID, VendorName FROM Vendor";
        DataSet objDs = new DataSet();
        SqlDataAdapter dAdapter = new SqlDataAdapter();
        dAdapter.SelectCommand = cmd;;
        conn.Open();
        dAdapter.Fill(objDs);
        conn.Close();

        if (objDs.Tables[0].Rows.Count > 0)
        {
            VendorList.DataSource = objDs.Tables[0];
            VendorList.DataTextField = "VendorName";
            VendorList.DataValueField = "VendorID";
            VendorList.DataBind();
            VendorList.Items.Insert(0,"-- Select --");
        } else {
             lblMsg.Text = "No Vendor Found";
        }
    }
}
</script>
<asp:DropDownList ID="VendorList" runat="server" AutoPostBack="True" >
</asp:DropDownList>

2) I create a Tes2.aspx page with this code to see if I can pull that Vendor dropdown list, but no luck.

<%@ Page Language="C#" %>
<%@ Register TagPrefix="uc" TagName="Vendor" 
    Src="Controls\Vendor.ascx" %>
<html>
<body>
Testing
<form runat="server">
    <uc:Vendor id="VendorList" 
        runat="server" 
        />
</form>
</body>

Obviously, I am new and must doing thing wrong. Can someone please help me or give me an example of a dropdown list in user control and how to include it in a form? Thanks!

Tim M. · Accepted Answer · 2012-10-04 00:26:28Z

2

The first problem I see is that you are inheriting from Page inside your UserControl:

public partial class _Default : System.Web.UI.Page

Inherit from UserControl instead.

// notice that I also renamed the class to match the control name
public partial class Vendor : System.Web.UI.UserControl

Using a Codebehind File

As @x0n pointed out, your user control code can be placed in a codebehind file (automatically created when you create a user control inside Visual Studio). User controls typically consist of a markup portion (.ascx), a codebehind (.ascx.cs), and a designer file (.ascx.designer.cs). HTML markup goes into the ASCX file, and binding code goes into the codebehind.

I'd suggest saving your code, deleting your current user control, and re-adding it through Visual Studio.

Sample Project Structure
enter image description here

Markup (ASCX) File

<%@ Control Language="C#" AutoEventWireup="true" CodeBehind="VendorListControl.ascx.cs" Inherits="MyNamespace.VendorListControl" %>
<asp:DropDownList runat="server" ID="ddlVendorList" />
<asp:Label runat="server" ID="lblMessage" />

Codebehind

using System;
using System.Configuration;
using System.Data;
using System.Data.SqlClient;

namespace MyNamespace
{
    public partial class VendorListControl : System.Web.UI.UserControl
    {
        protected void Page_Load( object sender, EventArgs e ) {
            if( !IsPostBack ) {
                FillVendors();
            }
        }

        private void FillVendors() {
            string strConn = ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString;
            System.Data.SqlClient.SqlConnection conn = new System.Data.SqlClient.SqlConnection( strConn );

            SqlCommand cmd = new SqlCommand();
            cmd.Connection = conn;
            cmd.CommandType = CommandType.Text;
            cmd.CommandText = "SELECT VendorID, VendorName FROM Vendor";

            DataSet objDs = new DataSet();
            SqlDataAdapter dAdapter = new SqlDataAdapter();
            dAdapter.SelectCommand = cmd; ;
            conn.Open();
            dAdapter.Fill( objDs );
            conn.Close();

            if( objDs.Tables[0].Rows.Count > 0 ) {
                this.ddlVendorList.DataSource = objDs.Tables[0];
                this.ddlVendorList.DataTextField = "VendorName";
                this.ddlVendorList.DataValueField = "VendorID";
                this.ddlVendorList.DataBind();
                this.ddlVendorList.Items.Insert( 0, "-- Select --" );
            }
            else {
                this.lblMessage.Text = "No Vendor Found";
            }
        }
    }
}

Alternate Method - Remove Class Declaration

If you don't want to add a codebehind file for some reason, remove the class declaration altogether and just include the code inside it.

<script runat="server">
    protected void Page_Load(object sender, EventArgs e){
        if (!IsPostBack){
            FillVendor();
        }
    }

    // etc
</script>

As a side note, I would put the data access logic in a separate class for proper separation/reuse, but the structure you've outlined should work once you've corrected the aforementioned problems.

edited Oct 4, 2012 at 0:26

answered Oct 4, 2012 at 0:01

Tim M.

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7 Comments

x0n Over a year ago

That's not entirely it - by placing the class definition in a <script runat=server> tag, _Default also becomes a nested class inside the runtime compiled ASCX class.

Tim M. Over a year ago

true, the class declaration should be removed altogether unless a code-behind is added.

Milacay Over a year ago

It works! Thank you Tim for providing detail info which really helped me to got it to work.

Milacay Over a year ago

I got it working to display the Dropdown list, but now I don't know what is the ID for the dropdown list. When I view the "Form Details" I see this "<select id="VendorList_ddlVendorList" name="VendorList$ddlVendorList" value="2">", but this not the right ID when I try to do the Insert Record, any idea?

Dean Over a year ago

@Milacay What do you mean by "Form Details" - where did you find that?

|

x0n · Accepted Answer · 2012-10-04 00:00:28Z

0

Don't place the definition of the class inside the ASCX itself. Create a separate CS file and reference the separate file with the CodeBehind attribute on the <%@ Control ... directive. The ASP.NET runtime will compile your ASCX and CS at first access.

answered Oct 4, 2012 at 0:00

x0n

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Comments

Dean · Accepted Answer · 2012-10-04 00:11:14Z

0

Are you using Visual Studio? If so, you should use the templates provided as it makes it a lot easier and you'd have avoided this problem all together. For example, to add a user control you can right-click the folder you want to put it in (this is in the Solution Explorer) and go Add -> New Item. Then select Web User Control, give it a name and click Add.

answered Oct 4, 2012 at 0:11

Dean

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4 Comments

Milacay Over a year ago

Thanks everyone for helping, especially @Tim. I finally got it working. Appreciated!

Milacay Over a year ago

I got it working to display the Dropdown list, but now I don't know what is the ID for the dropdown list.

Dean Over a year ago

Can you be more specific? Are you trying to use the ID in the C# code or with javascript?

Dean Over a year ago

@Milacay I just saw your comment to Tim: .Net changes the ID before it gets to the client so that there are no conflicts. So the ID you use in your C# code is "ddlVendorList" but if you are trying to get at the drop down list in the browser it will be different (like the "VendorList_ddlVendorList")

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