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How to manage NullReferenceException?

I want to make a form that user have to fill out it.
But I'm getting an error.
Model:
public UserReport Input;
[Key]
//[Required]
public string ReportID { get; set; }
[Required]
public string Description { get; set; }
[Required]
[DataType(DataType.DateTime)]
public string Date { get; set; }
Controller:
private ApplicationDbContext _userReport;
public UserReport Input;
public PageController(ApplicationDbContext userReport)
{
_userReport = userReport;
}
[HttpGet]
public IActionResult SendReport()
{
return View();
}
[Authorize]
[HttpPost]
public async Task<IActionResult> SendReport(UserReport userReport)
{
var user = new UserReport { Description = Input.Description, Date = Input.Date };
var r = await _userReport.AddAsync(user);
}
View:
#model UserReport
<div class="col-md-6">
<form id = "SendReport" method="post">
<div asp-validation-summary="All" class="text-danger"></div>
<div class="form-group">
<label asp-for="Input.Description"></label>
<input asp-for="Input.Description" class="form-control" />
<span asp-validation-for="Input.Description" class="text-danger"></span>
</div>
<div class="form-group">
<label asp-for="Input.Date"></label>
<input asp-for="Input.Date" class="form-control" />
<span asp-validation-for="Input.Date" class="text-danger"></span>
</div>
<button type = "submit" class="btn btn-primary">send report</button>
</form>
</div>
what is wrong with that?
It shows me this Error :System.NullReferenceException - Object reference not set to an instance of an object... who can help me to manage this error.
Show me where is my mistake please

I think you need to go back through the tutorials in the docs again. It doesn't seem like you really know what you're doing here. You've got a field named Input, which seems to be pulled from a Razor Page, but you're working in an MVC controller here. However, even that is off, because you'd typically see that as something like:
[BindProperty]
public UserReport Input { get; set; }
In a Razor Page. Here, it's not even a property, so even if this would normally do something, it wouldn't as a field, regardless.
The NullReferenceException comes because you reference this field, but never actually initialize it. Again, in a Razor Page (and if it was a property rather than a field), this would get filled with the post data (via BindProperty), but it doesn't work that way in a controller.
In your controller action, you've got a userReport param, so that is where the post data will go. However, since all the asp-for attributes in your view reference Input.Something, nothing will actually get bound to this param. This too seems to be pulled from a Razor Page, without considering that it only works this way in a Razor Page.
Long and short, it looks like you just copied code from other places, without actually understanding any of it or what it does, and cobbled it together into a controller and view. The whole thing is fundamentally broken top-down.

You have mixed with MVC and Razor Pages.
For MVC:
1.Model:
public class UserReport
{
[Key]
//[Required]
public string ReportID { get; set; }
[Required]
public string Description { get; set; }
[Required]
[DataType(DataType.DateTime)]
public string Date { get; set; }
}
2.SendReport.cshtml:
#model UserReport
<div class="col-md-6">
<form asp-action="SendReport" method="post">
<div asp-validation-summary="All" class="text-danger"></div>
<div class="form-group">
<label asp-for="Description"></label>
<input asp-for="Description" class="form-control" />
<span asp-validation-for="Description" class="text-danger"></span>
</div>
<div class="form-group">
<label asp-for="Date"></label>
<input asp-for="Date" class="form-control" />
<span asp-validation-for="Date" class="text-danger"></span>
</div>
<button type="submit" class="btn btn-primary">send report</button>
</form>
</div>
3.Controller:
public class UserReportsController : Controller
{
private readonly YourDbContext _context;
public UserReportsController(YourDbContext context)
{
_context = context;
}
public IActionResult SendReport()
{
return View();
}
[HttpPost]
public async Task<IActionResult> SendReport([Bind("ReportID,Description,Date")] UserReport userReport)
{
if (ModelState.IsValid)
{
_context.Add(userReport);
await _context.SaveChangesAsync();
return RedirectToAction(nameof(Index));
}
return View(userReport);
}
}
For Razor Pages:
1.Model:
public class UserReport
{
[Key]
//[Required]
public string ReportID { get; set; }
[Required]
public string Description { get; set; }
[Required]
[DataType(DataType.DateTime)]
public string Date { get; set; }
}
2.SendReport.cshtml:
#page
#model SendReportModel
<div class="col-md-6">
<form id="SendReport" method="post">
<div asp-validation-summary="All" class="text-danger"></div>
<div class="form-group">
<label asp-for="Input.Description"></label>
<input asp-for="Input.Description" class="form-control" />
<span asp-validation-for="Input.Description" class="text-danger"></span>
</div>
<div class="form-group">
<label asp-for="Input.Date"></label>
<input asp-for="Input.Date" class="form-control" />
<span asp-validation-for="Input.Date" class="text-danger"></span>
</div>
<button type="submit" class="btn btn-primary">send report</button>
</form>
</div>
3.SendReport.cshtml.cs:
public class SendReportModel : PageModel
{
private readonly YourDbContext _context;
public SendReportModel(YourDbContext context)
{
_context = context;
}
public IActionResult OnGet()
{
return Page();
}
[BindProperty]
public UserReport Input { get; set; }
public async Task<IActionResult> OnPostAsync()
{
if (!ModelState.IsValid)
{
return Page();
}
_context.UserReport.Add(Input);
await _context.SaveChangesAsync();
return RedirectToPage("./Index");
}
}
Reference:
Tutorial:Create a web app with ASP.NET Core MVC
Tutorial: Create a Razor Pages web app with ASP.NET Core

Why is my data binding not working and is always null?

I am trying to add data to the database. I experimenting with Blazor and .NET core:
This is my code in the controller:
[Route("AddCarBlazor")]
[HttpPost]
public IActionResult PostBlazor(Car car)
{
if (car.CarId == 0)
{
// New
car.Created = DateTime.Now;
_context.Cars.Add(car);
_context.SaveChanges();
return Ok();
}
else
{
// Update
var c = _context.Cars.First(e => e.CarId == car.CarId);
c.Brand = car.Brand;
c.Color = car.Color;
c.Model = car.Model;
c.LastChange = DateTime.Now;
c.TopSpeed = car.TopSpeed;
_context.SaveChanges();
return Ok();
}
}
My car model looks like this:
public class Car
{
[Key]
public long CarId { get; set; }
public string Created { get; set; }
public string LastChange { get; set; }
public string Brand { get; set; }
public string Model { get; set; }
public string Color { get; set; }
public long TopSpeed { get; set; }
}
I call this method like this:
private async Task AddCar()
{
await Http.PostJsonAsync(baseUrl + "/AddCarBlazor/", carobject);
await Refresh();
}
When I fill in the form and press add button the car object is always null
This is my form with the databinding:
<form>
<div class="row">
<div class="form-group col-sm-3">
<label>Brand</label>
<input input type="text" #bind="#carobject.Brand" class="form-control" placeholder="Enter brand" />
</div>
</div>
<div class="row">
<div class="form-group col-sm-3">
<label>Model</label>
<input type="text" #bind="#carobject.Model" class="form-control" placeholder="Enter model" />
</div>
</div>
<div class="row">
<div class="form-group col-sm-3">
<label>Color</label>
<input type="text" #bind="#carobject.Color" class="form-control" placeholder="Enter color" />
</div>
</div>
<div class="row">
<div class="form-group col-sm-3">
<label>TopSpeed</label>
<input type="number" #bind="#carobject.TopSpeed" class="form-control" placeholder="Enter speed" />
</div>
</div>
<div class="btn-group mr-2">
<button class="btn btn-danger mr-1" onclick=#AddCar>Save changes</button>
</div>
</form>
I have put a breakpoint on the addCar method. I get the values from the fields but when it goes to the controller it becomes null.
I have following this tutorial:
https://learn.microsoft.com/en-us/aspnet/core/blazor/call-web-api?view=aspnetcore-3.0
How can I save the values from the fields and send it to the database?

I test a demo which works well, you could refer to my code below:
1.Car.cs (namespace Blazor.Models)
public class Car
{
public long CarId { get; set; }
public string Brand { get; set; }
public string Model { get; set; }
}
2. AddCar.razor
#page "/car"
#using System.Net.Http
#inject HttpClient Http
#using Blazor.Models
<Editform Model="carobject">
<div class="row">
<div class="form-group col-sm-3">
<label>Brand</label>
<input #bind="#carobject.Brand" class="form-control" placeholder="Enter brand" />
</div>
</div>
<div class="row">
<div class="form-group col-sm-3">
<label>Model</label>
<input #bind="#carobject.Model" class="form-control" placeholder="Enter model" />
</div>
</div>
<div class="btn-group mr-2">
<button class="btn btn-danger mr-1" onclick="#AddCar">Save changes</button>
</div>
</Editform>
#functions {
[Parameter]
private Car carobject { get; set; } = new Car();
private async Task AddCar()
{
await Http.PostJsonAsync(baseUrl + "/AddCarBlazor/", carobject);
//await Refresh();
}
}
3.Web API CORS configuration:
app.UseCors(corsbuilder => {
corsbuilder.AllowAnyHeader().AllowAnyMethod().AllowAnyOrigin();
});
app.UseHttpsRedirection();
app.UseAuthentication();
app.UseMvc();
4.action:
[Route("AddCarBlazor")]
[HttpPost]
public IActionResult PostBlazor([FromBody]Car car)

After a weekend of research I have the solution!
I have changed my method in CarService.cs like this:
public async Task AddCar(Car car)
{
var client = new HttpClient { BaseAddress = new Uri("https://localhost:44369/api/car/") };
await client.SendJsonAsync(HttpMethod.Post, "AddCar", car);
}
Then I call this method in my razor page like this:
async Task AddCar()
{
await CarService.AddCar(car);
car = new CarService.Car();
await LoadCarData();
}
I also made a new object of the service like this:
CarService.Car car = new CarService.Car();
And I moved the model of Car.cs into CarService.cs

Data.Annotations like required and regularexpression not working on certain model

I can't seem to make the [Required] and [RegularExpression] data annotation to work on a certain model. On all other models it does work. When I do not enter any information in the fields of Address.cshtml, it still accepts it, and sends it to the database. On all other pages where required is used, it does work. So I must do something wrong I guess.
Address.cshtml.cs is where the InputModel is with the required fields.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.RazorPages;
using System.ComponentModel.DataAnnotations;
using Microsoft.AspNetCore.Identity;
using Microsoft.Extensions.Logging;
using bytme.Models;
using bytme.Data;
namespace bytme.Areas.Identity.Pages.Account.Manage
{
public class AddressModel : PageModel
{
private readonly UserManager<UserModel> _userManager;
private readonly SignInManager<UserModel> _signInManager;
private readonly ILogger<AddressModel> _logger;
private readonly ApplicationDbContext _context;
public AddressModel(
UserManager<UserModel> userManager,
SignInManager<UserModel> signInManager,
ILogger<AddressModel> logger,
ApplicationDbContext context)
{
_userManager = userManager;
_signInManager = signInManager;
_logger = logger;
_context = context;
}
[BindProperty]
public InputModel Input { get; set; }
public string ReturnUrl { get; set; }
[TempData]
public string StatusMessage { get; set; }
public class InputModel
{
[Required]
[DataType(DataType.Text)]
[Display(Name = "Name")]
[StringLength(100, ErrorMessage = "Invalid input. Maximum is 100 characters.")]
public string name { get; set; }
[Required]
[DataType(DataType.Text)]
[Display(Name = "Surname")]
[StringLength(100, ErrorMessage = "Invalid input. Maximum is 100 characters.")]
public string surname { get; set; }
[Required]
[DataType(DataType.Text)]
[Display(Name = "Street")]
[StringLength(48, ErrorMessage = "The longest street name in the Netherlands is 48 characters.")]
public string street { get; set; }
[Required]
[DataType(DataType.Text)]
[Display(Name = "House Number")]
[StringLength(5, ErrorMessage = "The longest house number in the Netherlands is 5 characters.")]
public string streetnumber { get; set; }
//[DataType(DataType.Text)]
//[Display(Name = "House Number Addition", Description = "For example A or II")]
//[StringLength(6, ErrorMessage = "
//public string streetnumberadd { get; set; }
[Required]
[DataType(DataType.Text)]
[Display(Name = "City")]
[StringLength(28, ErrorMessage = "The longest place name in the Netherlands is 28 characters.")]
public string city { get; set; }
[Required]
[DataType(DataType.PostalCode)]
[Display(Name = "Postal Code")]
[RegularExpression(#"^[1-9][0-9]{3}\s?[a-zA-Z]{2}$", ErrorMessage = "Invalid zip, for example: 1234AB")]
public string zipcode { get; set; }
}
public void OnGet(string returnUrl = null)
{
ReturnUrl = returnUrl;
}
public async Task<IActionResult> OnPostAsync()
{
var user = await _userManager.GetUserAsync(User);
if (user == null)
{
throw new ApplicationException($"Unable to load user with ID '{_userManager.GetUserId(User)}'.");
}
user.name = Input.name;
user.surname = Input.surname;
user.street = Input.street;
user.streetnumber = Input.streetnumber;
user.city = Input.city;
user.zipcode = Input.zipcode;
var changeAdresResult = _context.Users.Update(user);
_context.SaveChanges();
await _signInManager.SignInAsync(user, isPersistent: false);
_logger.LogInformation("User added their address information successfully.");
StatusMessage = "Your address information has been added.";
return RedirectToPage();
}
}
}
Address.cshtml is where the fields are made.
#page
#model AddressModel
#inject SignInManager<UserModel> SignInManager
#using Microsoft.AspNetCore.Identity
#using bytme.Models;
#{
ViewData["Title"] = "Add Address Information";
Layout = "~/Views/Shared/_Layout.cshtml";
}
#{
var hasExternalLogins = (await SignInManager.GetExternalAuthenticationSchemesAsync()).Any();
}
<div>
<h3>Change your account settings</h3>
<hr />
<div class="row">
<div class="col-md-3">
<partial name="_ManageNav" />
</div>
<div class="col-md-9">
<div class="row">
<div class="col-md-6">
<partial name="_StatusMessage" for="StatusMessage" />
<h4>#ViewData["Title"]</h4>
<form id="change-password-form" method="post">
<div asp-validation-summary="All" class="text-danger"></div>
<div class="form-group">
<label asp-for="Input.name"></label>
<input asp-for="Input.name" class="form-control" />
<span asp-validation-for="Input.name" class="text-danger"></span>
</div>
<div class="form-group">
<label asp-for="Input.surname"></label>
<input asp-for="Input.surname" class="form-control" />
<span asp-validation-for="Input.surname" class="text-danger"></span>
</div>
<div class="form-group">
<label asp-for="Input.street"></label>
<input asp-for="Input.street" class="form-control" />
<span asp-validation-for="Input.street" class="text-danger"></span>
</div>
<div class="form-group">
<label asp-for="Input.streetnumber"></label>
<input asp-for="Input.streetnumber" class="form-control" />
<span asp-validation-for="Input.streetnumber" class="text-danger"></span>
</div>
<div class="form-group">
<label asp-for="Input.city"></label>
<input asp-for="Input.city" class="form-control" />
<span asp-validation-for="Input.city" class="text-danger"></span>
</div>
<div class="form-group">
<label asp-for="Input.zipcode"></label>
<input asp-for="Input.zipcode" class="form-control" />
<span asp-validation-for="Input.zipcode" class="text-danger"></span>
</div>
<button type="submit" class="btn btn-default">Submit</button>
</form>
</div>
</div>
</div>
</div>
</div>
EDIT:
I noticed when editing the OnPostAsync to another name, for example AccountChange, that the data annotations do work. But I do need the OnPostAsync on the method, because on the view I use method="post", otherwise I can't send the information to the database.

I think you need to do your validation in OnPostAsync:
public async Task<IActionResult> OnPostAsync()
{
if (!ModelState.IsValid)
{
return Page(); // <-- model error
}
// continue with your post logic...
See here

My View is not see View Model and Giving an error

My View is not seeing view model and give An expression tree may not contain a dynamic operation. When I look for this error most of people didnt used #model xxx on the view. But I used it
This is my User Controller page
public class UserController : Controller
{
private readonly DbManager _context;
public UserController(DbManager context)
{
_context = context;
}
[HttpGet]
public IActionResult Kayit()
{
UserViewModel vm = new UserViewModel();
return View(vm);
}
[HttpPost]
public async Task<IActionResult> KayitAsync([Bind("Isim,Soyad,DogumTarihi,KullaniciAdi,Sifre")]Kullanici k)
{
if (ModelState.IsValid)
{
_context.Kullanicilar.Add(k);
await _context.SaveChangesAsync();
return View("thanks");
}
return View("Index");
}
}
This is my User/Kayit View
#Model ArtSite.ViewModels.UserViewModel
<h2>Kayıt Sayfası</h2>
<div class="row">
<div class="col-md-4">
<form asp-controller="User" asp-action="Kayit" method="post">
<div asp-validation-summary="All"></div>
<div>
<label asp-for="Isim"></label>
<input asp-for="Isim" />
<span asp-validation-for="Isim"></span>
</div>
<div>
<label asp-for="Soyad"></label>
<input asp-for="Soyad" />
<span asp-validation-for="Soyad"></span>
</div>
<div>
<label asp-for="DogumTarihi"></label>
<input type="date" asp-for="DogumTarihi" />
<span asp-validation-for="DogumTarihi"></span>
</div>
<div>
<label asp-for="KullaniciAdi"></label>
<input asp-for="KullaniciAdi" />
<span asp-validation-for="KullaniciAdi"></span>
</div>
<div>
<label asp-for="Sifre"></label>
<input type="password" asp-for="Sifre" />
<span asp-validation-for="Sifre"></span>
</div>
<div>
<label asp-for="ConfirmSifre"></label>
<input type="password" asp-for="ConfirmSifre" />
<span asp-validation-for="ConfirmSifre"></span>
</div>
<div><input type="submit" value="Kayıt Ol" /></div>
</form>
</div>
</div>
And this is the View Model i used for View
namespace ArtSite.ViewModels
{
public class UserViewModel
{
[Required]
public string Isim { get; set; }
[Required]
public string Soyad { get; set; }
[Required,DataType(DataType.Date),Display(Name = "Doğum Tarihi")]
public DateTime DogumTarihi { get; set; }
[Required,MinLength(6),MaxLength(30),Display(Name ="Kullanıcı Adı")]
public string KullaniciAdi { get; set; }
[Required,DataType(DataType.Password), MinLength(6), MaxLength(30)]
[Display(Name ="Şifre")]
public string Sifre { get; set; }
[Required, DataType(DataType.Password), MinLength(6), MaxLength(30)]
[Compare("Password",ErrorMessage ="Şifreniz Uyuşmadı."),Display(Name ="Şifreyi Onayla")]
public string ConfirmSifre { get; set; }
}
}
So please help me to understand it.

You are confusing between #Model property and #model directive, as they both are different things and have different purpose too. You need to put #model to define the model for view.
#model ArtSite.ViewModels.UserViewModel
Also refer to this post (mvc uppercase Model vs lowercase model
) for more detailed understanding of these.

ASP.NET MVC View needs to display data from a certain model and at the same time take input data for another model

I have a View which uses a dynamic object to pull data from multiple models declared in the ViewModel. However, within the same model I am trying to take user input via a form. The data is correctly displayed for the 2 models which are also part of the dynamic object. But I am UNSUCCESSFUL getting the form input, because I keep getting the error that the dynamic object is not accessible.[And this is for the form only.]
Here is how the View looks like
#model dynamic
#using ActionAugerMVC.ViewModels
#addTagHelper "*,Microsoft.AspNetCore.Mvc.TagHelpers"
<div class="course__title">
#Model.item.PageTitle
</div>
<p class="course__desc">
#Html.Raw(Model.item.PageText)
</p>
<div class="event__price">
<h3>#Model.item.NoticeTitle</h3>
<p>#Model.item.NoticeNeedItem</p>
<button type="submit" class="btn btn-accent">
Get A Quote Now
</button>
</div>
<h3 class="course_desc__title">Other Services</h3>
<ul class="course_requirements__list multi-column">
#foreach (var link in Model.data)
{
<li><i class="ion-android-arrow-forward"></i> #Html.ActionLink((string)link.PageTitle, "Page", "Plumbing", new { id = link.ID, url = link.PageURL }) </li>
}
</ul>
<div class="sidebar__item">
<p class="subheading">Instant Quote Request</p>
<form class="register__form" role="form" asp-controller="Plumbing" asp-action="Page" method="post">
<div class="text-danger" asp-validation-summary="All"></div>
<div class="form-group">
<label class="sr-only">Full Name </label>
<input asp-for="#Model.quote.FullName" type="text" class="form-control" placeholder="Full name">
</div>
<div class="form-group">
<label class="sr-only">Your phone</label>
<input asp-for="#Model.quote.Phone" type="tel" class="form-control" placeholder="Your phone">
<span asp-validation-for="#Model.quote.Phone" class="text-danger"></span>
</div>
<div class="form-group">
<label class="sr-only">E-mail</label>
<input asp-for="#Model.quote.Email" type="email" class="form-control" placeholder="E-mail">
<span asp-validation-for="#Model.quote.Email" class="text-danger"></span>
</div>
<div class="form-group">
<label class="sr-only">Your Message</label>
<input asp-for="#Model.quote.Message" type="text" class="form-control" placeholder="Your Message">
</div>
<input type="submit" value="Get a Quote Now" class="btn btn-accent btn-block">
</form>
</div> <!-- .sidebar__item -->
And here is how the controller looks like :-
public class PlumbingController : Controller
{
private readonly ActionAugerDataContext actionAugerDbContext;
private readonly UnitOfWork unitOfWork;
private readonly PlumbingPageViewModel plumbingViewModel;
public PlumbingController(ActionAugerDataContext context)
{
actionAugerDbContext = context;
unitOfWork = new UnitOfWork(actionAugerDbContext);
plumbingViewModel = new PlumbingPageViewModel(unitOfWork);
}
// GET: /<controller>/
public IActionResult Index()
{
var data = plumbingViewModel.PlumbingContent;
return View(data);
}
[HttpGet]
[Route("plumbing/calgary-{url}")]
public IActionResult Page(int ID, string url)
{
dynamic Page = new ExpandoObject();
Page.item = unitOfWork.ContentRepository.GetById(ID);
Page.data = plumbingViewModel.PlumbingContent;
Page.cities = plumbingViewModel.Cities;
// Page.quote = plumbingViewModel.Quote;
return View(Page);
}
[HttpPost]
public IActionResult Page(Quote quote)
{
return View();
}
}
Here is the View Model :-
public class PlumbingPageViewModel
{
public IEnumerable<Content> PlumbingContent { get; set; }
public IEnumerable<Cities> Cities { get; set; }
public Quote Quote { get; set; }
public PlumbingPageViewModel(UnitOfWork unitOfWork)
{
PlumbingContent = unitOfWork.ContentRepository
.GetAll()
.Where(d => d.Section == "Plumbing")
.Where(c => c.City == "Calgary");
Cities = unitOfWork.CitiesRepository
.GetAll()
.Where(c => c.HomeCity == "Calgary");
}
}
And here is the model class for the form.
public class Quote
{
public int ID { get; set; }
public string FullName { get; set; }
public string Phone { get; set; }
public string Email { get; set; }
public string City { get; set; }
public string Message { get; set; }
}

you can't you use dynamic model ( #model dynamic) for building your form with HtmlHelper
If you want Post form you should specific model.
Hope you this will you.