使用DropDownList

Question

我已经检查了重复的问题，但没有找到任何解决方案......

我正在研究“献血者”项目，但在“捐赠者列表”视图中，我正面临“对象引用未设置为对象的实例”错误。 我已经花了两天时间解决这个问题，但还没有得到任何解决方案。

型号：

     public class Donor
    {

    [Key]
    public int DonorId { get; set; }
    [Display(Name = "Donor Name")]
    [StringLength(25,ErrorMessage="Your name should be less than 25 characters")]
    [Required(ErrorMessage = "Enter your name")]
    public string DonorName { get; set; }

    [EmailAddress(ErrorMessage = "Invalid Pattern")]
    public string Email { get; set; }

    [Required(ErrorMessage = "Enter you address")]
    public string Address { get; set; }


    [Required(ErrorMessage = "Enter your password")]
    [DataType(DataType.Password)]
    public string Password { get; set; }
    [Display(Name = "Confirm Password")]
    [DataType(DataType.Password)]
    [Required(ErrorMessage = "Confirm your password")]
    [Compare("Password", ErrorMessage = "please confirm your password")]
    public string ConfirmPassword { get; set; }

    [Required(ErrorMessage = "Enter your age")]

    public int Age { get; set; }

    [Display(Name = "Mobile No")]
    [Required(ErrorMessage = "Enter you mobile number")]
    [StringLength(11,ErrorMessage="Must be 11 digits number")]

    public string MobileNo { get; set; }


    public bool IsAble { get; set; }

    public string Gender { get; set; }
    [Display(Name = "Blood Group")]
    public string BloodGroup { get; set; }


    }

控制器：

Here i have a static list for "Blood Groups"....


public ActionResult DonorsList()
    {
        var BGList = new List<SelectListItem> 
                { 
                    new SelectListItem{Text="A+ve",Value="1"},
                    new SelectListItem{Text="O+ve",Value="2"} 
                };
        ViewBag.LList = new SelectList(BGList, "Value", "Text","1");
            return View();

    }
    [HttpPost]
    public ActionResult DonorsList(Donor model, string ddlBloodGroups)
    {

        using (DataAccess db = new DataAccess())
        {
            var BGList = new List<SelectListItem> 
                { 
                    new SelectListItem{Text="A+ve",Value="1"},
                    new SelectListItem{Text="O+ve",Value="2"} 
                };
            ViewBag.LList = new SelectList(BGList, "Value", "Text","1");

            var obj = db.Donors.Where(m => m.BloodGroup == ddlBloodGroups).ToList();

            return View(obj);
    }

查看：

这就是我渲染下拉列表的方式......

@Html.DropDownList("ddlBloodGroups", ViewBag.LList as SelectList, "--Select--", new { @class = "form-control", style = "height:45px;font-size:18px;" })

        <input type="submit" value="Search" class="btn" style="margin-top:5px;background-color:#3F4A5C;border:2px solid white" />

[HttpGet]请求效果很好......

The DDL populated

但是当我通过选择DropDownList ...

为渲染html表添加以下代码时

<div class="row">
    <div class="col-md-12">
        <table>
            <tr>
                <th>Donor Name</th>
                @*<th>Email</th>
                <th>Mobile No</th>
                <th>Gender</th>
                <th>Age</th>
                <th>Address</th>
                <th>Blood Group</th>*@
            </tr>

            @foreach (var item in Model)
            {
                <tr>
                    <td>@item.DonorName</td>
                </tr>
            }

        </table>




    </div>
</div>

...比它给我“对象引用未设置为对象的实例”错误在[HTTPGET]请求

This is the error i'm facing