c# - How to use DropdownList selected Value to filter data -

i have dropdown,a textbox , button,dropddown contains columnnames (name,cpr),to see filtered data user selects value dropdown,enters string , clicks button. doing wrote following code,but unable dropdown selected value,except problem code working perfectly.plz tell me im doing mistake. following controller

 public actionresult index(string searchtype,formcollection frm)         {             list<selectlistitem> obj = new list<selectlistitem>();             obj.add(new selectlistitem { text = "agent name", value = "name", selected = true });             obj.add(new selectlistitem {text = "cpr number", value = "cpr"});             viewbag.cmb = obj;               var agents = s in db.agents                 select s;              if (searchtype != null)             {                 viewbag.searchstring = searchtype;                 string cmbcolumnselection = frm["cmb"];                  switch (cmbcolumnselection)                 {                     case "name": // table=agent,column=name                          agents = agents.where(s => s.name.tostring().contains(searchtype));                         break;                     default:                         agents = agents.where(s => s.cpr.tostring().contains(searchtype));                         break;                 }             }              return view(agents.tolist());         }  ` 

in view:

    @using (html.beginform("index", "agent", formmethod.get))     {         <p>             @html.textbox("searchtype", viewbag.searchstring string)             select filter : @html.dropdownlist("cmb")             <input type="submit" value="submit" class="btn btn-primary" />         </p>    } 

don't mix action input parameters , form collection. have start searchtype, stick same cmb , drop form collection altogether:

public actionresult index(string searchtype, string cmb) 

that's it, cmb contain value posted drop down. use now:

string cmbcolumnselection = cmb; 

or even

switch (cmb) {...