asp.net mvc 4 - Cascade Drop down list -

i trying create cascading drop down list, , getting error.

this contains try in controller class:

public actionresult create() {     viewbag.status = new selectlist(db.pjt_statuses, "pjt_status_id", "statusname");     viewbag.categoryid = new selectlist(db.pjt_categories, "pjt_category_id", "catname");     return view(); }  public actionresult subcategory(int id) {     var subcategory = s in db.pjt_subcategories                       s.categoryid == id                      select s;     return json(subcategory.tolist()); }  // post: /project/create [httppost] public actionresult create(pjt_projects pjt_projects) {     if (modelstate.isvalid)     {         pjt_projects.creationdate = datetime.now;         db.pjt_projects.add(pjt_projects);         db.savechanges();         return redirecttoaction("index");     }      viewbag.status = new selectlist(db.pjt_statuses, "pjt_status_id", "statusname", pjt_projects.status);     viewbag.categoryid = new selectlist(db.pjt_categories, "pjt_category_id", "catname", pjt_projects.categoryid);     return view(pjt_projects); } 

view

this shows try on front end. getting error bold line in view code below. error getting is:

there no viewdata item of type ienumerable<selectlistitem> has key pjt_subcat_id.

code:

<div class="span3 offset1">     @html.labelfor(model => model.categoryid, "category")     @html.dropdownlist("categoryid", string.empty)@*, null, new { @onchange = "fetchsubcategories();" })*@     <br />     @html.validationmessagefor(model => model.categoryid) </div> <div class="span3 offset1">     <label>sub category</label>         @html.dropdownlist("pjt_subcat_id", string.empty)     <br />     @html.validationmessagefor(model => model.subcategoryid) </div> 

can advise me going wrong here?

the problem engine trying selectlist viewbag , cannot find it. guessing want dropdown display items have stored in viewbag under "pjt_subcat_id" not adding item viewbag anywhere in code have listed in question.

if supposed data returned subcategory() method, not find data in viewbag , should have javascript calls method on click event of original selectlist (category id one) , binds returned data subcategory one.