DownDownList问题显示类型

Question

我正在使用Intranet，特别是每周监控工具，该工具可让我逐周看到我的员工的活动。我正在致力于逐周过滤器。到目前为止，我已经找到了如何创建一个包含List 2015年每星期按以下格式：

From dd/mm/yyyy to dd/mm/yyyy 

像这样：

public ActionResult WeeklyMonitoring() 
{ 
    ProjectResourceManagerService pr = new ProjectResourceManagerService(new ModelStateWrapper(this.ModelState)); 

    List<string> wl = pr.FetchWeeks(DateTime.Now.Year); // Creates the list 
    ViewBag.Weeks = wl; 
    wl.Select(m => new SelectListItem { Text = m, Value = m });   
    return View(); 
} 

但这里的问题，当我选择一个星期我DropDownList（这里我不得不将其转换为正确的类型）：

<td><%: Html.DropDownList("Weeks", ((List<string>)ViewBag.Weeks).Select(m => new SelectListItem { Text = m, Value = m }), new { onchange = "this.form.submit();"}) %></td> 

它发送至：

[HttpPost] 
public ActionResult WeeklyMonitoring(FormCollection form) 
{ 
    string week = form["Weeks"];    

    ViewBag.Weeks = week; 
    return View(); 
} 

我得到了明显的以下错误：

无法转换类型 '字符串' 到 'System.Collections.Generic.List'

我怎么可能避免这个错误，并保持表格发送后我的DropDownList选定的一周？

编辑：

到目前为止，我已经发现了这个解决方案，可能不是一个过滤器实用但在这里我去：

[HttpPost] 
public ActionResult WeeklyMonitoring(FormCollection form) 
{ 
    string week = form["Weeks"];   

    ProjectResourceManagerService pr = new ProjectResourceManagerService(new ModelStateWrapper(this.ModelState)); 

    List<string> wl = pr.FetchWeeks(DateTime.Now.Year); 
    wl.Remove(week); 
    wl.Insert(0, week); 
    wl.Select(m => new SelectListItem { Text = m, Value = m }); 
    ViewBag.Weeks = wl; 
    return View(); 
} 

我从列表中删除的项目，并把它放在顶部，所以它由DDList显示。

EDIT2：

添加FetchWeeks：

public List<string> FetchWeeks(int year) 
    { 
     List<string> weeks = new List<string>(); 
     DateTime startDate = new DateTime(year, 1, 1); 
     startDate = startDate.AddDays(1 - (int)startDate.DayOfWeek); 
     DateTime endDate = startDate.AddDays(6); 
     while (startDate.Year < 1 + year) 
     { 
      weeks.Add(string.Format("From {0:dd/MM/yyyy} to {1:dd/MM/yyyy}", startDate, endDate)); 
      startDate = startDate.AddDays(7); 
      endDate = endDate.AddDays(7); 
     } 
     return weeks; 
    } 

EDIT3：由于kikyalex我们已经找到了解决办法：

当ViewBag属性具有相同的名称创建一个问题DDList阻止它改变它的价值。

Answer 1

string week = form["Weeks"];    

ViewBag.Weeks = week; 

从下拉列表中获取当前星期并将其传递到视图中。然后你把它作为List<string>。发生错误是正常的。

您应该SelectListItem

public ActionResult WeeklyMonitoring() 
{ 
    ProjectResourceManagerService pr = new ProjectResourceManagerService(new ModelStateWrapper(this.ModelState)); 

    List<string> wl = pr.FetchWeeks(DateTime.Now.Year); // Creates the list 
    ViewBag.Weeks = wl.Select(m => new SelectListItem { Text = m, Value = m }).ToList(); 
    return View(); 
} 

[HttpPost] 
public ActionResult WeeklyMonitoring(FormCollection form) 
{ 
    string week = form["Weeks"];   

    ProjectResourceManagerService pr = new ProjectResourceManagerService(new ModelStateWrapper(this.ModelState)); 

    List<string> wl = pr.FetchWeeks(DateTime.Now.Year); 
    ViewBag.Weeks = wl.Select(m => new SelectListItem { Text = m, Value = m, Selected = m == week }).ToList(); 
    return View(); 
} 

在您查看铸造改为List<SelectListItem>而不是List<string>

<td><%: Html.DropDownList("Weeks", ((List<SelectListItem>)ViewBag.Weeks), new { onchange = "this.form.submit();"}) %></td>