更新用户信息时，视图模型为null

Question

错误：NullReferenceException：对象引用未设置为对象实例。网状物控制器。ManageController。ManageController.cs中的ChangeUser(BaseViewModel模型(+使用者FirstName=型号。ChangeUserViewModel。FirstName；

我不明白为什么我会犯这个错误，你能帮我找出我做错了什么吗？

我试图实现的是通过我的视图模型更新用户信息。

你能告诉我做这件事的方式是否正确吗？

BaseViewModel：

public class BaseViewModel
{
public IndexViewModel IndexViewModel { get; set; }
public ChangeUserViewModel ChangeUserViewModel { get; set; }
}

更改用户视图模型：

public class ChangeUserViewModel
{
[Required]
[StringLength(20, ErrorMessage = "The {0} must be at least {2} characters long.", MinimumLength = 1)]
public string FirstName { get; set; }
[Required]
[StringLength(20, ErrorMessage = "The {0} must be at least {2} characters long.", MinimumLength = 1)]
public string LastName { get; set; }

[Required]
[EmailAddress]
[Display(Name = "Email")]
public string Email { get; set; }

[Display(Name = "Profile Picture")]
[DataType(DataType.Upload)]
[MaxFileSize(5* 1024 * 1024)]
[AllowedExtensions(new string[] { ".jpg", ".png", ".jpeg", ".gif", ".tif" })]
public IFormFile ProfilePicture { get; set; }
}

控制器：

public async Task<IActionResult> Index()
{
var user = await GetCurrentUserAsync();
var model = new BaseViewModel
{
IndexViewModel = new IndexViewModel
{
HasPassword = await _userManager.HasPasswordAsync(user),
PhoneNumber = await _userManager.GetPhoneNumberAsync(user),
TwoFactor = await _userManager.GetTwoFactorEnabledAsync(user),
Logins = await _userManager.GetLoginsAsync(user),
BrowserRemembered = await _signInManager.IsTwoFactorClientRememberedAsync(user),
AuthenticatorKey = await _userManager.GetAuthenticatorKeyAsync(user),
},
ChangeUserViewModel = new ChangeUserViewModel
{
FirstName = user.FirstName,
LastName = user.LastName,
Email = user.Email
}
};
return View(model);
}
[HttpPost]
[ValidateAntiForgeryToken]
public async Task<IActionResult> ChangeUser(BaseViewModel model)
{
if (!ModelState.IsValid)
{
return RedirectToAction("Index", "Manage");
}

var user = await GetCurrentUserAsync();
if (user != null)
{
user.FirstName = model.ChangeUserViewModel.FirstName;
user.LastName = model.ChangeUserViewModel.LastName;
user.Email = model.ChangeUserViewModel.Email;
await _userManager.UpdateAsync(user);
}
return View("Index", model);
}

视图：

@model BaseViewModel
@inject UserManager<ApplicationUser> UserManager
@{
ViewData["Title"] = "Manage your account";
}
<h2 class="content-heading pt-0">
<i class="fa fa-fw fa-user-circle text-muted mr-1"></i> User Profile
</h2>

<form asp-controller="Manage" asp-action="ChangeUser" method="post" class="form-horizontal" role="form" enctype="multipart/form-data">
<div class="row push">
<div class="col-lg-4">
<p class="text-muted">
Your account’s vital info.
</p>
</div>

<div asp-validation-summary="All" class="text-danger"></div>
<div class="col-lg-8 col-xl-5">
<div class="form-group">
<label for="dm-profile-edit-firstname">Firstname</label>
<input asp-for="ChangeViewModel.FirstName" type="text" class="form-control" id="dm-profile-edit-firstname" name="dm-profile-edit-firstname" >
</div>
<div class="form-group">
<label for="dm-profile-edit-lastname">Lastname</label>
<input asp-for="ChangeViewModel.LastName" type="text" class="form-control" id="dm-profile-edit-lastname" name="dm-profile-edit-lastname">
</div>
<div class="form-group">
<label for="dm-profile-edit-email">Email Address</label>
<input asp-for="ChangeViewModel.Email" type="email" class="form-control" id="dm-profile-edit-email" name="dm-profile-edit-email">
</div>
<div class="form-group">
<label>Your Avatar</label>
<div class="push">
<img class="img-avatar" src="@Url.Action("ProfilePicture", "Account" )" alt="">
</div>
<div class="custom-file">
<input asp-for="ChangeViewModel.ProfilePicture" type="file" class="custom-file-input js-custom-file-input-enabled" data-toggle="custom-file-input" id="ProfilePicture" name="ProfilePicture">
<label class="custom-file-label" for="ProfilePicture">Choose a new avatar</label>
</div>
</div>

<div class="form-group">
<button type="submit" class="btn btn-alt-primary">
<i class="fa fa-check-circle mr-1"></i> Update Profile
</button>
</div>
</div>
</div>
</form>

Answer 1

在从视图发布请求时，控制器似乎没有收到BaseViewModel。我建议你可以用Newtonsoft’s Json.NET代替System.Text.Json。

步骤1.安装以下Nuget包

Install-Package Microsoft.AspNetCore.Mvc.NewtonsoftJson

步骤2。如果你是从一个现有的项目迁移过来的，你会调用"AddMvc(("，然后你可以像这样粘贴到它上：

services.AddMvc().AddNewtonsoftJson();

然而，在新的.NET Core3+项目中，您有一组不同的调用来替换MVC。因此，您可能会遇到以下情况之一：

services.AddControllers().AddNewtonsoftJson();
services.AddControllersWithViews().AddNewtonsoftJson();
services.AddRazorPages().AddNewtonsoftJson();

然后，在控制器代码中放置断点，以检查BaseViewModel model的值。