登記表：ViewData的產品類型的「system.sting」必應「的IEnumerable <selectlistitem>

Question

我使用MVC3剃刀和我想打一個登記表，我可以選擇用下拉列表的作用。

我得到的角色在下拉列表和所有的，但是當我點擊提交我得到：

具有關鍵的角色「爲System.String類型，但必須是IEnumerable<SelectListItem>類型的ViewData項目

我的代碼

型號：

[Required] 
    [Display(Name = "Select role: ")] 
    public String Role { get; set; } 

我的控制器：

public ActionResult Register() 
    { 
     List<SelectListItem> list = new List<SelectListItem>(); 
     SelectListItem item; 
     foreach (String role in Roles.GetAllRoles()) 
     { 
      item = new SelectListItem{ Text = role, Value = role}; 
      list.Add(item); 
     } 

     ViewBag.roleList = (IEnumerable<SelectListItem>)list; 
     return View(); 
    } 

我交控制器：

[HttpPost] 
    public ActionResult Register(RegisterModel model) 
    { 
     if (ModelState.IsValid) 
     { 
      // Attempt to register the user 
      MembershipCreateStatus createStatus; 
      Membership.CreateUser(model.UserName, model.Password, model.Email, null, null, true, null, out createStatus); 

      if (createStatus == MembershipCreateStatus.Success) 
      { 
       Roles.AddUserToRole(model.UserName, model.Role); 
       return RedirectToAction("Index", "Home"); 
      } 
      else 
      { 
       ModelState.AddModelError("", ErrorCodeToString(createStatus)); 
      } 
     } 

     // If we got this far, something failed, redisplay form 
     return View(model); 
    } 

我的觀點：

<div class="editor-label"> 
      @Html.LabelFor(m => m.Role) 
     </div> 
     <div class="editor-field"> 
      @Html.DropDownListFor(m => m.Role, ViewBag.roleList as IEnumerable<SelectListItem>) 
      @Html.ValidationMessageFor(m => m.Role) 

     </div> 

當我使用調試器來檢查我的碼，在控制器中，當我查看參數模型並在model.Role處看到右邊的字符串。 有誰知道我的問題的任何解決方案？

Answer 1

在您的文章的行動，你不再植中的情況下ViewBag的roleList，當你重新顯示視圖：

... 
// If we got this far, something failed, redisplay form 

// but before redisplaying the form ensure that we have populated the 
// ViewBag.roleList that this form depends on 
ViewBag.roleList = ... same stuff as your GET action 
return View(model); 

這是說，我會建議你擺脫ViewBag並添加RoleList財產您的視圖模型：

public class RegisterModel 
{ 
    [Required] 
    [Display(Name = "Select role: ")] 
    public string Role { get; set; } 

    public IEnumerable<SelectListItem> RoleList 
    { 
     get 
     { 
      return Roles 
       .GetAllRoles() 
       .Select(x => new SelectListItem 
       { 
        Value = x, 
        Text = x 
       }) 
       .ToList(); 
     } 
    } 
} 

然後：

public ActionResult Register() 
{ 
    var model = new RegisterModel(); 
    return View(model); 
} 

[HttpPost] 
public ActionResult Register(RegisterModel model) 
{ 
    if (ModelState.IsValid) 
    { 
     // Attempt to register the user 
     MembershipCreateStatus createStatus; 
     Membership.CreateUser(model.UserName, model.Password, model.Email, null, null, true, null, out createStatus); 
     if (createStatus == MembershipCreateStatus.Success) 
     { 
      Roles.AddUserToRole(model.UserName, model.Role); 
      return RedirectToAction("Index", "Home"); 
     } 
     else 
     { 
      ModelState.AddModelError("", ErrorCodeToString(createStatus)); 
     } 
    } 

    // If we got this far, something failed, redisplay form 
    return View(model); 
} 

和強類型視圖：

@model RegisterModel 
... 

<div class="editor-label"> 
    @Html.LabelFor(m => m.Role) 
</div> 
<div class="editor-field"> 
    @Html.DropDownListFor(m => m.Role, Model.RoleList) 
    @Html.ValidationMessageFor(m => m.Role) 
</div> 

沒有更多ViewBag =>沒有問題。