Multiple Selection in Dropdown and update query string

Question

I generate a report according to selection of company and their customer. I use one dropdown for company and according to company the customer is displayed. However, I want to make it possible to select multiple customers, and when the user clicks on the button to the view report, I want to update the query string with that selection. If the selection of customer is three, I want to pass their customer code using query string. In sort querystring is send according to the selection of customer.

Please help me.

Thanks and regards.

Mitesh

Answer 1

In your selection page (aspx):

...
<script type="text/javascript">
        function submitSelection() {
            var customerList = document.getElementById('<%= lbCustomers.ClientID %>');
            var companyList = document.getElementById('<%= lbCompany.ClientID %>');
            var selectedCustomerQuery = [];
            for (var i = 0; i < customerList.options.length; i++) {                
                if (customerList.options[i].selected)
                    selectedCustomerQuery.push('customer_id=' + customerList.options[i].value);
            }
            location.href = 'Report.aspx?company_id=' + companyList.value + '&' + selectedCustomerQuery.join('&');
        }
    </script>
        <asp:DropDownList ID="lbCompany" runat="server" SelectionMode="Single" >
        <asp:ListItem Value="1">Company 1</asp:ListItem>
        <asp:ListItem Value="2">Company 2</asp:ListItem>
    </asp:DropDownList><br />
    <asp:ListBox ID="lbCustomers" runat="server" SelectionMode="Multiple">
        <asp:ListItem Text="John" Value="1"></asp:ListItem>
        <asp:ListItem Text="Paul" Value="2"></asp:ListItem>
        <asp:ListItem Text="Peter" Value="3"></asp:ListItem>
    </asp:ListBox><br />
    <input id="Button1" type="button" value="View Report" onclick="submitSelection()" />
...

Then in your Report.aspx.cs:

...
protected void Page_Load(object sender, EventArgs e)
        {
            var selectedCompany = Request.QueryString["company_id"];
            //get passed selected customers, will be stored in an array
            var selectedCustomers = Request.QueryString.GetValues("customer_id");

            Response.Write(string.Format("Company ID: {0}, Customers: {1}", selectedCompany.ToString(), string.Join(",", selectedCustomers)));
        }
...

This illustrates an example without posting back to the page. If you need to post back to handle other logic in your code behind, you'll have to change the <input> button to an ASP.NET button control and handle its OnClick event.