ASP.NET MVC中为DropDownListFor设置选中项的方法

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public ActionResult SomeAction(int id)

{

  //从数据库获取Domain Model

  var domainModel = ModelService.LoadEntities(m => m.ID == id).FirstOrDefault<Model>();

  //通过某个方法获取List<SelectListItem>类型对象实例

  List<SelectListItem> items = SomeMethod();

  //遍历集合，如果当前Domain model的某个属性与SelectListItem的Value属性相等，把SelectListItem的Selected属性设置为true

  foreach(SelectListItem item in items)

  {

    if(item.Value == Convert.ToString(domainModel.某属性))

    {

      item.Selected = true;

    }

  }

  //把List<SelectListItem>集合对象实例放到ViewData中

  ViewData["somekey"] = items;

  //可能涉及到把Domain Model转换成View Model

  return PartialView(domainModel);

}

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public class Department

{

  public int Id {get;set;}

  public string Name {get;set;}

  public bool IsSelected {get;set;}

}

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public ActionResult Index()

{

 SampleDbContext db = new SampleDbContext();

 List<SelectListItem> selectListItems = new List<SelectListItem>();

 //遍历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();

}

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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);//根据返回的选中项值设置选中项 

        ViewData["ruturned"] = collection["drop"];

       }

       ViewData["drop"] = selec;

      return View();

    }