dausa's questions

我正在做一个项目，涉及到在ASP.Net Core 7.0中使用select选项，我遇到了一些困难。具体来说，我在下拉列表中遇到了与空引用异常相关的错误。但是我观察到，提交数据后，安装到SQL数据库中，提交后返回时，显示空引用异常错误。这些错误使开发过程变得相当具有挑战性，我希望尽快找到解决方案。任何意见或建议将不胜感激。

错误

行动

public IActionResult Apply()
{

    ViewBag.Courselist = new SelectList(GetAllAccountIDList(), "Id", 
    "CourseName");
    return View();
}
[HttpPost]
public IActionResult Apply(PurchasedFormViewModel purchasedFormVM)
{
    if (ModelState.IsValid)
    {
    try
    {
        var transaction = new StudentBiodataViewModels
        {
            CourseId = purchasedFormVM.CourseId,
            SurName = purchasedFormVM.SurName,
            OtherName = purchasedFormVM.OtherName,
            PhoneNumber = purchasedFormVM.PhoneNumber,
            Email = purchasedFormVM.Email,
        };
        _context.StudentBiodata.Add(transaction);
        _context.SaveChangesAsync();
    }
    catch (Exception ex)
    {

        ViewBag.Message = ex.Message + " Error occur while inserting records.";
    }
    }
    return View();
}

楷模

 public class ApplyFormViewModel
 { 
     public int Id { get; set; }
     [Display(Name = "Course Apply")]
     [Required(ErrorMessage = "Course Apply is Required")]
     public int CourseId { get; set; }
     [Display(Name = "SurName")]
     [Required(ErrorMessage = "SurName is Required")]
     public string SurName { get; set; }
     [Display(Name = "Other Name")]
     [Required(ErrorMessage = "Other Name is Required")]
     public string OtherName { get; set; } 
     [Display(Name = "Phone Number")]
     [Required(ErrorMessage = "Phone Number is Required")]
     ErrorMessage = "Entered phone format is not valid.")]
     public string PhoneNumber { get; set; } 
     [Required(ErrorMessage = "Email is Required")]
     public string Email { get; set; }
     
 }

看法

<select id="fundcode" asp-for="CourseId" class="form-control">
    <option value="">--Please select--</option>
    @foreach (var item in ViewBag.Courselist )
    {
        <option value="@item.Value">@item.Text</option>
    }
</select>

我正在使用ASP.Net Core 7.0并尝试显示DateTime.Now到输入框中，但在加载页面时没有显示任何内容。

请参阅下面我的所有代码。

模型

public class DateShowVM
{
   [DataType(DataType.Date)]
   [DisplayFormat(DataFormatString = "{0:dd/MM/yyyy}", ApplyFormatInEditMode = true)]
   public DateTime TranDate { get; set; }
}

行动

public IActionResult Index()
 {
    ViewBag.datenow = Convert.ToDateTime(DateTime.Now.ToString("dd/MM/yyyy"));
    
    return View();
 }

看法

<div class="form-group">
    <label asp-for="TranDate" class="control-label"></label>
    <input asp-for="TranDate" value="@ViewBag.datenow" readonly class="form-control" />
    <span asp-validation-for="TranDate" class="text-danger"></span>
</div>