如何修复基于 id 编辑页面的错误？

Question

当我点击编辑按钮时出现错误，它在 img src 中显示错误（空引用）

这是成员控制器的编辑功能

public async Task<IActionResult> Edit(int memberId)
        {
            var memeber = await _context.Member.FindAsync(memberId); // Getting member by Id from database
            return View(new MemberViewModel() { Member = memeber });

        }

        [HttpPost]
        [ValidateAntiForgeryToken]
        public async Task<IActionResult> Edit(MemberViewModel model, IFormFile photo/*int id, [Bind("MemberId,Name,Gender,DOB,MaritalStatus,Address,PhoneNo,Skills,Hobbies,JobTitle,Technology")] Member member*/)
        {
            if (photo == null || photo.Length == 0)
            {
                return Content("File not selected");
            }
   
            var path = Path.Combine(_webHostEnviroment.WebRootPath, "ImageName/Cover", photo.FileName);
            using (FileStream stream = new FileStream(path, FileMode.Create))
            {
                await photo.CopyToAsync(stream);
                stream.Close();
            }
            model.Member.ImageName = photo.FileName;

            //Finding the member by its Id which we would update
            var objMember = _context.Member.Where(mId => mId.MemberId == model.Member.MemberId).FirstOrDefault();

            if (objMember != null)
            {
                //Update the existing member with new value
                objMember!.Name = model.Member.Name;
                objMember!.Gender = model.Member.Gender;
                objMember!.DOB = model.Member.DOB;
                objMember!.MaritalStatus = model.Member.MaritalStatus;
                objMember!.Address = model.Member.Address;
                objMember!.PhoneNo = model.Member.PhoneNo;
                objMember!.Skills = model.Member.Skills;
                objMember!.Hobbies = model.Member.Hobbies;
                objMember!.JobTitle = model.Member.JobTitle;
                objMember!.Technology = model.Member.Technology;
                objMember!.ImageName = model.Member.ImageName;
                objMember!.ImageLocation = path;

                await _context.SaveChangesAsync();
            }
            return RedirectToAction("Index");

        }

这是一个出现错误的视图

@model TeamManagement.ViewModel.MemberViewModel

<form asp-action="Edit" method="post" enctype="multipart/form-data">
<div class="row">
        <div class="form-group col-md-4">
            <label class="col-md-2 control-label">MemberPicture</label>
            <div class="col-md-10">
                <img src="~/ImageName/Cover/@Model.Member.ImageName"
                     class="rounded-square"
                     height="50" width="75"
                     style="border:1px"
                     asp-append-version="true" accept="image/*" />
                <span><a href="@Model.Member.ImageName">@Model.Member.ImageName</a></span>
                <div id="chooseFile">
                    <input class="form-control" type="file" name="photo" accept="image/*" />
                </div>
            </div>
        </div>
    </div>

这是我的 ViewModel 名称 MemberVieModel

using System;
using TeamManagement.Models;

namespace TeamManagement.ViewModel
{
    public class MemberViewModel
    {
        public Member Member { get; set; }
        public IFormFile? Photo { get; set; }
    }
}

查看模型截图

那是我尝试了你的代码，当我在我的代码上实施时 运行 他们给出了那个错误

Answer 1

I get error when I click on edit button it show error in img src (null reference)

这是因为您没有按照说明进行操作。您没有在 form 的开头设置 <input type="hidden" asp-for="Member.MemberId" />，因此编译器无法获取需要更新 Id 的 Id。因此，将 form 顶部的 Member.MemberId 设置为隐藏项，对于 'edit':

是强制性的

您将在以下位置遇到的错误：

  var objMember = _context.Member.Where(mId => mId.MemberId == model.Member.MemberId).FirstOrDefault();

注意：当你不在你的form设置<input type="hidden" asp-for="Member.MemberId" />时，它不会得到需要更新的引用并抛出你得到的错误。

解法：

<form asp-action="EditMember" method="post" enctype="multipart/form-data">
            <div asp-validation-summary="ModelOnly"></div>
            <input type="hidden" asp-for="Member.MemberId" />
 </form>

还有一点：

确保您已将 [Key] 设置在 Member 模型的顶部。它应该如下所示：

public class Member
    {
        [Key]
        public int MemberId { get; set; }
        [StringLength(60, MinimumLength = 3)]

        public string? Name { get; set; }

        public string? Gender { get; set; }
        public DateTime DOB { get; set; }

        public string? ImageName { get; set; }
        public string? ImageLocation { get; set; }
       
    }