Introduction

Sometimes, we may come across a situation where we have few DropDownLists and when we select a value from a particular DropDown, all the other DropDowns should reset to their default value. Here, I have given a solution for that situation.

Using the Code

Let us assume that you have this table structure which includes 3 DropDownLists and a Text Box which displays the selection you made in the DropDownList.

<table>
  <tbody>
     <tr style="width: 100%">
         <th colspan="3">
             This is to reset all other dropdownlist when a dropdowns selection changes
         </th>
     </tr>
     <tr>
         <td>
            <asp:DropDownList ID="DropDownList1" 
            onchange="DisableOtherDropdowns(this)" runat="server">
            </asp:DropDownList>
         </td>
         <td>
             <asp:DropDownList ID="DropDownList2" 
             onchange="DisableOtherDropdowns(this)" runat="server">
             </asp:DropDownList>
         </td>
         <td>
             <asp:DropDownList ID="DropDownList3" 
             onchange="DisableOtherDropdowns(this)" runat="server">
             </asp:DropDownList>
         </td>
     </tr>
     <tr style="width: 100%">
         <td>
             <asp:Label ID="lblSelectedField" 
             runat="server" Text="Selected Text"></asp:Label>
         </td>
         <td>
             <asp:TextBox ID="txtSelectedText" 
             runat="server"></asp:TextBox>
         </td>
    </tr>
  </tbody>
</table>

Now I have created a DataTable with 2 columns and binded that to the DropDownLists.

 DataTable dt = new DataTable();
            dt.Columns.Add("Student Id");
            dt.Columns.Add("Student Name");

            DataRow dr = dt.NewRow();
            dr["Student Id"] = "1";
            dr["Student Name"] = "Mahesh";
            dt.Rows.Add(dr);
//Include as many rows you need and bound it to the DropDown Lists. I have done it for one DropDownList.
// Method is similar to others also.

  DropDownList1.DataSource = dt;
            DropDownList1.DataTextField = "Student Name";
            DropDownList1.DataValueField = "Student Id";
            DropDownList1.DataBind();

Now this is the most important part.

<script src="//ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<script type="text/javascript">
    function DisableOtherDropdowns(obj) {
        var currentDropDownId = obj.id;
        var currentDropDownText = obj.options[obj.selectedIndex].text;
        $('table select').each(function () {
            var dropId = this.id;
            if (dropId != currentDropDownId) {
                this.selectedIndex = 0;
            }
        });
        $('#<%= txtSelectedText.ClientID %>').val(currentDropDownText);
    }
</script>

I have included JQuery CDN. In the script, I'm targeting all DropDowns which are present inside the HTML Table.

When the selection of a DropDownList changes, this script executes. You can see currentDropDownText stores the current selected Value of the DropDown and I'm setting that value to a Text Box simply to see which value is currently selected.

Note

This is really a simple program. There might be other solutions and if you know any, let me know. It is always nice to know more than one approach to solve a problem.

Resetting All Other DropDownLists When a Selection of a Particular DropDownList Changes