Razor - 通過Ajax.BeginForm將DropDownList選定值傳遞給控制器​​

Question

我試圖將dropdownlist值傳遞給我的控制器，所以我可以將值添加到一個paycodes列表，但我不斷收到「值不能爲空」。錯誤。我的支付代碼列表中有很多項目。不知道什麼是空或錯在這裏...

內部異常

Value cannot be null. 
Parameter name: source 

VIEW

 <!-- products input--> 
     <div class="control-group col-lg-6"> 
      <label class="control-label">Product</label> 
      <div class="controls"> 
       @using (Ajax.BeginForm("AddPayCode", "Referral", 
    new AjaxOptions() 
    { 
     HttpMethod = "POST", 
     InsertionMode = InsertionMode.Replace, 
     UpdateTargetId = "PayCodes", 
     Url = Url.Action("AddPayCode", "Referral") 
    })) 
       { 
        @Html.ValidationSummary() 

        @Html.DropDownListFor(model => model.SelectedPayCode, new SelectList(Model.PayCodes.ToList(), "Id", "Description"), "- Select -") 
        <input type="submit" value="Add" /> 
       } 
      </div> 
     </div> 

控制器

[HttpPost] 
public void AddPayCode(ReferralModel model) 
{ 
    var test = model.SelectedPayCode; 
    //TODO: Add to model.Referral.PayCodes list and return list of selected items 
} 

模型

public class ReferralModel 
{ 
    public Customer Customer { get; set; } 
    public Employee Employee { get; set; } 
    public List<PayCode> PayCodes { get; set; } 
    public int SelectedPayCode { get; set; } 

    public Referral Referral { get; set; } 
} 

域對象

public class Referral 
{ 
    [Key] 
    public int Id { get; set; } 
    public int CustomerId { get; set; } 
    public int EmployeeId { get; set; } 
    public decimal Total { get; set; } 

    public virtual List<PayCode> PayCodes { get; set; } 
    public virtual Customer Customer { get; set; } 
    public virtual Employee Employee { get; set; } 
} 

目的：

• 用戶從下拉菜單中選擇一個paycode並點擊 「添加」 Paycode是

• 添加到介PayCodes列表

• 控制器返回選擇到視圖的付費代碼列表（不是 尚未實施）

Answer 1

問題是控制器缺少下拉列表的屬性。

[HttpPost] 
public void AddPayCode(ReferralModel model, ** string SelectedPayCode ** <-- missing) 
{ 
    var test = SelectedPayCode; 
    //TODO: Add to model.Referral.PayCodes list and return list of selected items 
}