My standard way to work with dropdown box in ASP.NET MVC – 2 steps (or 3 if you want to add long description)

I have written a small post about dropdownlist template in ASP.NET MVC here : http://msprogrammer.serviciipeweb.ro/2010/05/30/mvc-helper-templates/

I think that the dropdownlist should be explained more – aand the example will be :

First, let’s say we have Employee and Department. And we have Employee that has a field, named IDDepartment.

When edit/create a user we want to display a dropdownlist for Department in order for the user to choose the department.

Step 1 : obtain from database a list of departments and transform into List<KeyValuePair<string,string>>  – where the first string is DepartmentID and the second is Department Name.

Let’s say there is a method to do that : deptList.Values

Step 2 : display into the aspx/ascx file with List_KVP template

<%: Html.EditorFor(model => model.deptList.Values, “List_KVP”, “IDDepartment”, new { SelectedValue = Model.emp.IDDepartment })%>

Here is the weak part: the “IDDepartment” is not strongly typed. You can transform that …but it requires writing another extension. However, when you modify the code for

SelectedValue = Model.emp.IDDepartment

it is right nearby…

For reference, here is the List_KVP.ascx

<%@ Control Language="C#" Inherits="System.Web.Mvc.ViewUserControl<List<System.Collections.Generic.KeyValuePair<string,string>>>" %>
<%
    string Val = "",style="";
    if(ViewData.Values != null && ViewData.Values.Count > 0)
    {
        Val = (ViewData["SelectedValue"]??"").ToString();
        style = (ViewData["Style"] ?? "").ToString();
    }
    if (style.Length > 0)
    {

    }
    var id=ViewData.TemplateInfo.GetFullHtmlFieldId("") ;
    id = id + "";
    %>

<select id="<%:id %>" name="<%:ViewData.TemplateInfo.GetFullHtmlFieldName("") %>" style="<%: style %>">
    <% foreach (var val in Model)
       { %>
            <option  value='<%: val.Key %>' <%:(val.Key == Val)?"selected=selected":"" %>><%: val.Value %></option>
    <%} %>
</select>
<% if(Model.Exists(x=>x.Key ==Val) )
{
       %>
       <script type="text/javascript">
   $(document).ready(function () {

       $('#<%:id  %>').change();
   }     );
      </script>
      <%
}
    %>

Oh, and if you ask how to add a description , nothing more simple :
Step1 : add to dropdown an onchange event : onchange=’javascript:funcDepartmentRetrieve(this)”
Step 2: create a java script function that retrieves the long description from the id

 <script type="text/javascript">
         <%: Html.JavaScriptFind( Model.deptList.LongDescriptionValues, "funcDepartmentLong","notfoundDepartment") %>
        </script>

Step 3 : Mix the 2 javascript functions

For your reference, the code for JavaScriptFind is

 public static MvcHtmlString JavaScriptFind(this HtmlHelper hh, ICollection<KeyValuePair<string,string>> values, string Name, string NotFound)
        {
            string s = "function " + Name + "(value){  switch(value){";
            string ret = "case '{0}' : return '{1}';" + Environment.NewLine;
            foreach (var item in values)
            {
                //TODO : compensate for '
                s += string.Format(ret, item.Key, item.Value);
            };
            s += string.Format("default : return '{0}' ;//+ value;"  + Environment.NewLine, NotFound);
            s += "};";//switch
            s += "}";//function
            return MvcHtmlString.Create(s);
        }