ASP.NET MVC中為DropDownListFor設置選中項的方法

public ActionResult SomeAction(int id)
{
 //從數據庫獲取Domain Model
 var domainModel = ModelService.LoadEntities(m => m.ID == id).FirstOrDefault<Model>();
 
 //通過某個方法獲取List<SelectListItem>類型對象實例
 List<SelectListItem> items = SomeMethod();
 
 //遍歷集合，如果當前Domain model的某個屬性與SelectListItem的Value屬性相等，把SelectListItem的Selected屬性設置為true
 foreach(SelectListItem item in items)
 {
 if(item.Value == Convert.ToString(domainModel.某屬性))
 {
 item.Selected = true;
 }
 }
 
 //把List<SelectListItem>集合對象實例放到ViewData中
 ViewData["somekey"] = items;
 
 //可能涉及到把Domain Model轉換成View Model
 
 return PartialView(domainModel);
}

public class Department
{
 public int Id {get;set;}
 public string Name {get;set;}
 public bool IsSelected {get;set;}
}

public ActionResult Index()
{
 SampleDbContext db = new SampleDbContext();
 List<SelectListItem> selectListItems = new List<SelectListItem>();
 
 //遍歷Department的集合
 foreach(Department department in db.Departments)
 {
 SelectListItem = new SelectListItem
 {
 Text = department.Name,
 Value = department.Id.ToString(),
 Selected = department.IsSelected.HasValue ? department.IsSelected.Value : false
 }
 selectListItems.Add(selectListItem);
 }
 ViewBag.Departments = selectListItems;
 return View();
}

public ActionResult Index(FormCollection collection)
 {
 IList<Project> li = Utility.SqlHelper.getProjectList();
 SelectList selec = new SelectList(li, "ID", "Name");
 
 if (collection["drop"] != null)
 {
 string projectID = collection["drop"];
 selec = new SelectList(li, "ID", "Name", projectID);//根據返回的選中項值設置選中項 
 ViewData["ruturned"] = collection["drop"];
 }
 ViewData["drop"] = selec;
 return View();
 }