[Solved] DropDownList with CheckBoxes in ASP.Net

try this then :

Step 1: Add a new form “dropdownlist.aspx” to the current project.

Step 2: Add a PlaceHolder control on to the form.

<asp:PlaceHolder ID="PlaceHolder1" runat="server"></asp:PlaceHolder>

Step 3: Add a HiddenField control on to the form.

<asp:HiddenField ID="HiddenField1" runat="server" />

Step 4: Add a Button control on to the form and change the Text property to “GetCheckedItems”

<asp:Button ID="Button1" runat="server" Text="GetCheckedItems" />

Step 5: Add a Label control on to the form and change the Text property to empty .

<asp:Label ID="Label1" runat="server"></asp:Label>

 Step 6: Do double click on the Button control; the button click event will gets generated.

<asp:Button ID="Button1" runat="server" onclick="Button1_Click" 
            Text="GetCheckedItems" />

 Step 7:Add a new namespace.

using System.Data;

step 8: copy and paste the bellow function into the code behind file.

This function is used to create a drop down list and checkbox list at runtime and items at run time.

public void ddl_checkbox()
        {
            DropDownList dropdownlist = new DropDownList();
            dropdownlist.ID = "dropdownlist_Item";
            ListItem lstItem = new ListItem();
            dropdownlist.Items.Insert(0, "select");
            dropdownlist.Items.Insert(1, lstItem);
            dropdownlist.Width = new Unit(155);
            dropdownlist.Attributes.Add("onmousedown", "showdivonClick()");

            CheckBoxList CheckboxList = new CheckBoxList();
            CheckboxList.ID = "CheckboxList_Item";
            CheckboxList.Attributes.Add("onmouseover", "showdiv()");

            DataTable datatable_ListItem = new DataTable();
            datatable_ListItem.Columns.Add("ID", typeof(int));
            datatable_ListItem.Columns.Add("Value", typeof(string));
            datatable_ListItem.Rows.Add(1, "Australia");
            datatable_ListItem.Rows.Add(2, "Bangladesh");
            datatable_ListItem.Rows.Add(3, "China");
            datatable_ListItem.Rows.Add(4, "India");
            datatable_ListItem.Rows.Add(5, "Jamaica");
            datatable_ListItem.Rows.Add(6, "Kenya");
            datatable_ListItem.Rows.Add(7, "Mexico");

            int rowNo = datatable_ListItem.Rows.Count;
            string listValue = string.Empty;
            string listID = string.Empty;

            for (int i = 0; i < rowNo - 1; i++)
            {
                listValue = datatable_ListItem.Rows[i]["Value"].ToString();
                listID = datatable_ListItem.Rows[i]["ID"].ToString();
                lstItem = new ListItem("<a href=\"javascript:void(0)\" id=\"alst\" style=\"text-decoration:none;color:Black; \" onclick=\"getSelectedItem(' " + listValue + "','" + i + "','" + listID + "','anchor');\">" + listValue + "</a>", datatable_ListItem.Rows[i]["ID"].ToString());
                lstItem.Attributes.Add("onclick", "getSelectedItem('" + listValue + "','" + i + "','" + listID + "','listItem');");
                CheckboxList.Items.Add(lstItem);
            }

            System.Web.UI.HtmlControls.HtmlGenericControl div = new System.Web.UI.HtmlControls.HtmlGenericControl("div");
            div.ID = "divChkList";
            div.Controls.Add(CheckboxList);
            div.Style.Add("border", "black 1px solid");
            div.Style.Add("width", "150px");
            div.Style.Add("height", "100px");
            div.Style.Add("overflow", "AUTO");
            div.Style.Add("display", "none");
            PlaceHolder1.Controls.Add(dropdownlist);
            PlaceHolder1.Controls.Add(div);
        }

 Step 9: copy the below code inside the button click event

protected void Button1_Click(object sender, EventArgs e) { }

string strSelectedItem = string.Empty;
            CheckBoxList check = (CheckBoxList)PlaceHolder1.FindControl("CheckboxList_Item");
            DropDownList ddl = (DropDownList)Page.FindControl("dropdownlist_Item");
      for (int i = 0; i < check.Items.Count; i++)
      {
            if (check.Items[i].Selected)
            {
                  if (strSelectedItem.Length == 0)
                  {
                        strSelectedItem = check.Items[i].Text.ToString();
                  }
                  else
                  {
                        strSelectedItem = strSelectedItem + "," + check.Items[i].Text.ToString();
                  }
            }
      }
      ddl.Items.Clear();
      ddl.Items.Add(new ListItem(HiddenField1.Value));
      Label1.Text = strSelectedItem;

 Step 10: call the ddl_checkbox() function inside the page load event.

protected void Page_Load(object sender, EventArgs e)
        {
            ddl_checkbox();
        }

 Step 11: copy and paste the below javascript inside the <head></head> tag in the html code.

<script language="javascript" type="text/javascript">
        function showdiv() {
            document.getElementById("divChkList").style.display = "block";
        }

        function showdivonClick() {
            var objDLL = document.getElementById("divChkList");
            if (objDLL.style.display == "block")
                objDLL.style.display = "none";
            else
                objDLL.style.display = "block";
        }

        function getSelectedItem(lstValue, lstNo, lstID, ctrlType) {
            var noItemChecked = 0;
            var ddlReport = document.getElementById("dropdownlist_Item");
            var selectedItems = "";
            var arr = document.getElementById("CheckboxList_Item").getElementsByTagName('input');
            var arrlbl = document.getElementById("CheckboxList_Item").getElementsByTagName('label');
            var objLstId = document.getElementById('HiddenField1');
            for (i = 0; i < arr.length; i++) {
                checkbox = arr[i];
                if (i == lstNo) {
                    if (ctrlType == 'anchor') {
                        if (!checkbox.checked) {
                            checkbox.checked = true;
                        }
                        else {
                            checkbox.checked = false;
                        }
                    }
                }
                if (checkbox.checked) {
                    if (selectedItems == "") {
                        selectedItems = arrlbl[i].innerText;
                    }
                    else {
                        selectedItems = selectedItems + "," + arrlbl[i].innerText;
                    }
                    noItemChecked = noItemChecked + 1;
                }
            }
            ddlReport.title = selectedItems;
            var Text = ddlReport.options[ddlReport.selectedIndex].text;
            if (noItemChecked == 1)
                ddlReport.options[ddlReport.selectedIndex].text = lstValue;
            else
                ddlReport.options[ddlReport.selectedIndex].text = noItemChecked + " Items";
            document.getElementById('HiddenField1').value = ddlReport.options[ddlReport.selectedIndex].text;
        }

        document.onclick = check;
        function check(e) {
            var target = (e && e.target) || (event && event.srcElement);
            var obj = document.getElementById('divChkList');
            var obj1 = document.getElementById('dropdownlist_Item');
            if (target.id != "alst" && !target.id.match("CheckboxList_Item")) {
                if (!(target == obj || target == obj1)) {
                    obj.style.display = 'none'
                }
                else if (target == obj || target == obj1) {
                    if (obj.style.display == 'block') {
                        obj.style.display = 'block';
                    }
                    else {
                        obj.style.display = 'none';
                        document.getElementById('dropdownlist_Item').blur();
                    }
                }
            }
        }
</script>

Now run the program and see the output:

Design:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
     <script language="javascript" type="text/javascript">
         function showdiv() {
             document.getElementById("divChkList").style.display = "block";
         }

         function showdivonClick() {
             var objDLL = document.getElementById("divChkList");
             if (objDLL.style.display == "block")
                 objDLL.style.display = "none";
             else
                 objDLL.style.display = "block";
         }

         function getSelectedItem(lstValue, lstNo, lstID, ctrlType) {
             var noItemChecked = 0;
             var ddlReport = document.getElementById("dropdownlist_Item");
             var selectedItems = "";
             var arr = document.getElementById("CheckboxList_Item").getElementsByTagName('input');
             var arrlbl = document.getElementById("CheckboxList_Item").getElementsByTagName('label');
             var objLstId = document.getElementById('HiddenField1');
             for (i = 0; i < arr.length; i++) {
                 checkbox = arr[i];
                 if (i == lstNo) {
                     if (ctrlType == 'anchor') {
                         if (!checkbox.checked) {
                             checkbox.checked = true;
                         }
                         else {
                             checkbox.checked = false;
                         }
                     }
                 }
                 if (checkbox.checked) {
                     if (selectedItems == "") {
                         selectedItems = arrlbl[i].innerText;
                     }
                     else {
                         selectedItems = selectedItems + "," + arrlbl[i].innerText;
                     }
                     noItemChecked = noItemChecked + 1;
                 }
             }
             ddlReport.title = selectedItems;
             var Text = ddlReport.options[ddlReport.selectedIndex].text;
             if (noItemChecked == 1)
                 ddlReport.options[ddlReport.selectedIndex].text = lstValue;
             else
                 ddlReport.options[ddlReport.selectedIndex].text = noItemChecked + " Items";
             document.getElementById('HiddenField1').value = ddlReport.options[ddlReport.selectedIndex].text;
         }

         document.onclick = check;
         function check(e) {
             var target = (e && e.target) || (event && event.srcElement);
             var obj = document.getElementById('divChkList');
             var obj1 = document.getElementById('dropdownlist_Item');
             if (target.id != "alst" && !target.id.match("CheckboxList_Item")) {
                 if (!(target == obj || target == obj1)) {
                     obj.style.display = 'none'
                 }
                 else if (target == obj || target == obj1) {
                     if (obj.style.display == 'block') {
                         obj.style.display = 'block';
                     }
                     else {
                         obj.style.display = 'none';
                         document.getElementById('dropdownlist_Item').blur();
                     }
                 }
             }
         }
</script>
</head>
<body>
    <form id="form1" runat="server">
    <div>

        <asp:PlaceHolder ID="PlaceHolder1" runat="server"></asp:PlaceHolder>
        <br />
        <asp:HiddenField ID="HiddenField1" runat="server" />
        <asp:Button ID="Button1" runat="server" onclick="Button1_Click" 
            Text="GetCheckedItems" />
        <br />
        <asp:Label ID="Label1" runat="server"></asp:Label>
        <br />

    </div>
    </form>
</body>
</html>

 C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;

namespace Demoasp
{
    public partial class dropdownlist : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            ddl_checkbox();
        }

        protected void Button1_Click(object sender, EventArgs e)
        {
            string strSelectedItem = string.Empty;
            CheckBoxList check = (CheckBoxList)PlaceHolder1.FindControl("CheckboxList_Item");
            DropDownList ddl = (DropDownList)Page.FindControl("dropdownlist_Item");
            for (int i = 0; i < check.Items.Count; i++)
            {
                if (check.Items[i].Selected)
                {
                    if (strSelectedItem.Length == 0)
                    {
                        strSelectedItem = check.Items[i].Text.ToString();
                    }
                    else
                    {
                        strSelectedItem = strSelectedItem + "," + check.Items[i].Text.ToString();
                    }
                }
            }
            ddl.Items.Clear();
            ddl.Items.Add(new ListItem(HiddenField1.Value));
            Label1.Text = strSelectedItem;
        }

        public void ddl_checkbox()
        {
            DropDownList dropdownlist = new DropDownList();
            dropdownlist.ID = "dropdownlist_Item";
            ListItem lstItem = new ListItem();
            dropdownlist.Items.Insert(0, "select");
            dropdownlist.Items.Insert(1, lstItem);
            dropdownlist.Width = new Unit(155);
            dropdownlist.Attributes.Add("onmousedown", "showdivonClick()");

            CheckBoxList CheckboxList = new CheckBoxList();
            CheckboxList.ID = "CheckboxList_Item";
            CheckboxList.Attributes.Add("onmouseover", "showdiv()");

            DataTable datatable_ListItem = new DataTable();
            datatable_ListItem.Columns.Add("ID", typeof(int));
            datatable_ListItem.Columns.Add("Value", typeof(string));
            datatable_ListItem.Rows.Add(1, "Australia");
            datatable_ListItem.Rows.Add(2, "Bangladesh");
            datatable_ListItem.Rows.Add(3, "China");
            datatable_ListItem.Rows.Add(4, "India");
            datatable_ListItem.Rows.Add(5, "Jamaica");
            datatable_ListItem.Rows.Add(6, "Kenya");
            datatable_ListItem.Rows.Add(7, "Mexico");

            int rowNo = datatable_ListItem.Rows.Count;
            string listValue = string.Empty;
            string listID = string.Empty;

            for (int i = 0; i < rowNo - 1; i++)
            {
                listValue = datatable_ListItem.Rows[i]["Value"].ToString();
                listID = datatable_ListItem.Rows[i]["ID"].ToString();
                lstItem = new ListItem("<a href=\"javascript:void(0)\" id=\"alst\" style=\"text-decoration:none;color:Black; \" onclick=\"getSelectedItem(' " + listValue + "','" + i + "','" + listID + "','anchor');\">" + listValue + "</a>", datatable_ListItem.Rows[i]["ID"].ToString());
                lstItem.Attributes.Add("onclick", "getSelectedItem('" + listValue + "','" + i + "','" + listID + "','listItem');");
                CheckboxList.Items.Add(lstItem);
            }

            System.Web.UI.HtmlControls.HtmlGenericControl div = new System.Web.UI.HtmlControls.HtmlGenericControl("div");
            div.ID = "divChkList";
            div.Controls.Add(CheckboxList);
            div.Style.Add("border", "black 1px solid");
            div.Style.Add("width", "150px");
            div.Style.Add("height", "100px");
            div.Style.Add("overflow", "AUTO");
            div.Style.Add("display", "none");
            PlaceHolder1.Controls.Add(dropdownlist);
            PlaceHolder1.Controls.Add(div);
        }
    }
}

 VB.NET

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;

namespace Demoasp
{
    public partial class dropdownlist : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            ddl_checkbox();
        }

        protected void Button1_Click(object sender, EventArgs e)
        {
            string strSelectedItem = string.Empty;
            CheckBoxList check = (CheckBoxList)PlaceHolder1.FindControl("CheckboxList_Item");
            DropDownList ddl = (DropDownList)Page.FindControl("dropdownlist_Item");
            for (int i = 0; i < check.Items.Count; i++)
            {
                if (check.Items[i].Selected)
                {
                    if (strSelectedItem.Length == 0)
                    {
                        strSelectedItem = check.Items[i].Text.ToString();
                    }
                    else
                    {
                        strSelectedItem = strSelectedItem + "," + check.Items[i].Text.ToString();
                    }
                }
            }
            ddl.Items.Clear();
            ddl.Items.Add(new ListItem(HiddenField1.Value));
            Label1.Text = strSelectedItem;
        }

        public void ddl_checkbox()
        {
            DropDownList dropdownlist = new DropDownList();
            dropdownlist.ID = "dropdownlist_Item";
            ListItem lstItem = new ListItem();
            dropdownlist.Items.Insert(0, "select");
            dropdownlist.Items.Insert(1, lstItem);
            dropdownlist.Width = new Unit(155);
            dropdownlist.Attributes.Add("onmousedown", "showdivonClick()");

            CheckBoxList CheckboxList = new CheckBoxList();
            CheckboxList.ID = "CheckboxList_Item";
            CheckboxList.Attributes.Add("onmouseover", "showdiv()");

            DataTable datatable_ListItem = new DataTable();
            datatable_ListItem.Columns.Add("ID", typeof(int));
            datatable_ListItem.Columns.Add("Value", typeof(string));
            datatable_ListItem.Rows.Add(1, "Australia");
            datatable_ListItem.Rows.Add(2, "Bangladesh");
            datatable_ListItem.Rows.Add(3, "China");
            datatable_ListItem.Rows.Add(4, "India");
            datatable_ListItem.Rows.Add(5, "Jamaica");
            datatable_ListItem.Rows.Add(6, "Kenya");
            datatable_ListItem.Rows.Add(7, "Mexico");

            int rowNo = datatable_ListItem.Rows.Count;
            string listValue = string.Empty;
            string listID = string.Empty;

            for (int i = 0; i < rowNo - 1; i++)
            {
                listValue = datatable_ListItem.Rows[i]["Value"].ToString();
                listID = datatable_ListItem.Rows[i]["ID"].ToString();
                lstItem = new ListItem("<a href=\"javascript:void(0)\" id=\"alst\" style=\"text-decoration:none;color:Black; \" onclick=\"getSelectedItem(' " + listValue + "','" + i + "','" + listID + "','anchor');\">" + listValue + "</a>", datatable_ListItem.Rows[i]["ID"].ToString());
                lstItem.Attributes.Add("onclick", "getSelectedItem('" + listValue + "','" + i + "','" + listID + "','listItem');");
                CheckboxList.Items.Add(lstItem);
            }

            System.Web.UI.HtmlControls.HtmlGenericControl div = new System.Web.UI.HtmlControls.HtmlGenericControl("div");
            div.ID = "divChkList";
            div.Controls.Add(CheckboxList);
            div.Style.Add("border", "black 1px solid");
            div.Style.Add("width", "150px");
            div.Style.Add("height", "100px");
            div.Style.Add("overflow", "AUTO");
            div.Style.Add("display", "none");
            PlaceHolder1.Controls.Add(dropdownlist);
            PlaceHolder1.Controls.Add(div);
        }
    }
}

or if u wish u could also do that this way :

http://www.codeproject.com/Articles/132359/Converting-ASP-NET-Control-Check-Box-List-into-Dro