对象引用未设置到对象 ViewData["Title"] = "Index" 的实例；

Question

所以我正在尝试使用模式在我的索引页面中创建一个注册剃刀页面。我导入模态的大部分表单代码来自现有的外部注册页面。但是，当我启动 mvc 应用程序时，我收到 Object reference not set to an instance of an object 错误。任何帮助，将不胜感激。谢谢！

控制台：

System.NullReferenceException: Object reference not set to an instance of an object.at AspNetCore.Views_Home_Index.ExecuteAsync() in C:\Users\SalvadorSolis\source\repos\AWSCognitoMVC\AWSCognitoMVC\Views\Home\Index.cshtml:line 4

HTML:

@page
@model AWSCognitoMVC.Views.Home.IndexModel
@{
    ViewData["Title"] = "Index";//line 4
}
<h2>@ViewData["Title"]</h2>

型号：

namespace AWSCognitoMVC.Views.Home
{
    [AllowAnonymous]
    public class IndexModel : PageModel
    {
        private readonly SignInManager<CognitoUser> _signInManager;
        private readonly CognitoUserManager<CognitoUser> _userManager;
        private readonly ILogger<IndexModel> _logger;
        private readonly CognitoUserPool _pool;

        public IndexModel(
            UserManager<CognitoUser> userManager,
            SignInManager<CognitoUser> signInManager,
            ILogger<IndexModel> logger,
            CognitoUserPool pool)
        {
        _userManager = userManager as CognitoUserManager<CognitoUser>;
        _signInManager = signInManager;
        _logger = logger;
        _pool = pool;
    }

    [BindProperty]
    public InputModel Input { get; set; }

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

        [Required]
        [StringLength(15, ErrorMessage = "The {0} must be at least {2} and at max {1} characters long.", MinimumLength = 10)]
        [Phone]
        [Display(Name = "Phone Number")]
        public string PhoneNumber { get; set; }

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

        [Required]
        [StringLength(100, ErrorMessage = "The {0} must be at least {2} and at max {1} characters long.", MinimumLength = 6)]
        [DataType(DataType.Password)]
        [Display(Name = "Password")]
        public string Password { get; set; }

        [DataType(DataType.Password)]
        [Display(Name = "Confirm password")]
        [Compare("Password", ErrorMessage = "The password and confirmation password do not match.")]
        public string ConfirmPassword { get; set; }
    }
    public void OnGet()
    {
    }

    public async Task<IActionResult> OnPostAsync(string returnUrl = null)
    {
        //Added because users don't usually add in a + in their phone number
        if (!(Input.PhoneNumber.First() == '+'))
        {
            Input.PhoneNumber = "+" + Input.PhoneNumber;
        }
        //Added because users don't usually add in a + in their phone number

        returnUrl = returnUrl ?? Url.Content("~/");
        if (ModelState.IsValid)
        {
            var user = _pool.GetUser(Input.UserName);

            user.Attributes.Add(CognitoAttributesConstants.Email, Input.Email);
            user.Attributes.Add(CognitoAttributesConstants.PreferredUsername, Input.UserName);
            user.Attributes.Add(CognitoAttributesConstants.PhoneNumber, Input.PhoneNumber);

            var result = await _userManager.CreateAsync(user, Input.Password);
            if (result.Succeeded)
            {
                _logger.LogInformation("User created a new account with password.");

                await _signInManager.SignInAsync(user, isPersistent: false);

                return RedirectToPage("./ConfirmAccount");
            }
            foreach (var error in result.Errors)
            {
                ModelState.AddModelError(string.Empty, error.Description);
            }
        }
        return Page();
    }
}
}

家庭控制器：

namespace AWSCognitoMVC.Controllers
{
    public class HomeController : Controller
    {
        public IActionResult Index()
        {
            return View();
        }

        public IActionResult Privacy()
        {
            return View();
        }

        [ResponseCache(Duration = 0, Location = ResponseCacheLocation.None, NoStore = true)]
        public IActionResult Error()
        {
            return View(new ErrorViewModel { RequestId = Activity.Current?.Id ?? HttpContext.TraceIdentifier });
        }
    }
}

注意：原始寄存器模型没有定义 "Title" 并且不知何故工作正常。

Answer 1

ViewData 是一个容器，用于将数据从 PageModel 传递到内容页面。

所以我想以这种方式在 PageModel 端设置数据是有意义的：

public class IndexModel : PageModel
{
    [ViewData]
    public string Title{ get; set; }

    public void OnGet()
    {
        Title = "Index";
    }

    // ...
}

然后就这样得到它：

<h2>@ViewData["Title"]</h2>

Answer 2

您正在尝试将控制器和视图方法与剃刀页面混合使用。只是不要这样做。如果您想使用 razor pages，请在项目的根目录中创建 Pages 文件夹，并在其中创建您的 razor 页面。如果您想通过 /home/index url 显示剃刀页面的视图，请在 Pages 文件夹中创建 Home 文件夹并在其中添加您的 IndexModel。

Pages\Home\Index.cshtml

阅读更多in the docs。

对象引用未设置到对象 ViewData["Title"] = "Index" 的实例；

Object reference not set to an instance of an object ViewData["Title"] = "Index";

c#

asp.net-core-mvc

asp.net-core

razor-pages