c# - Register.razor 中的错误:System.NullReferenceException:“对象引用未设置为对象的实例。”
问题描述
我正在 Blazor (C#) 服务器端做一个应用程序。我在 Register.razor 文件中收到以下错误: System.NullReferenceException: 'Object reference not set to an instance of an object。<> 4__this._dataContext 为空。我还收到以下警告:字段 Register._dataContext 从未分配给,并且始终具有其默认值 null。当我想将注册数据保存到数据库时(单击“注册”按钮),此错误发生在我身上。
我究竟做错了什么?
注册剃须刀:
@page "/register"
@using TestBlazor.Models
@using TestBlazor.Data
@*@inject IToDoListService user*@
<br />
<br />
<h3><b>Register</b></h3>
<br />
<EditForm class="needs-validation" Model="@_user" OnValidSubmit="@HandleValidSubmit" OnInvalidSubmit="@HandleInvalidSubmit">
<div class="alert @StatusClass">@StatusMessage</div>
<DataAnnotationsValidator />
<ValidationSummary />
<div class="form-group">
<p><b>User name</b></p>
<input id="username" class="solid" name="username" placeholder="Your username.." @bind-value="_user.UserName" />
<ValidationMessage For="@(() => @_user.UserName)"></ValidationMessage>
</div>
<div class="form-group">
<p><b>Password</b></p>
<input type="password" class="solid" id="password" placeholder="Your password.." @bind-value="_user.Password" />
<ValidationMessage For="@(() => @_user.Password)"></ValidationMessage>
</div>
<div class="form-group">
<p><b>Email</b></p>
<input id="email" class="solid" placeholder="you@example.com" @bind-value="_user.Email" />
<ValidationMessage For="@(() => @_user.Email)"></ValidationMessage>
</div>
<div class="form-group">
<p><b>Company</b></p>
<input id="company" class="solid" placeholder="Your company.." @bind-value="_user.Company" />
<ValidationMessage For="@(() => @_user.Company)"></ValidationMessage>
</div>
<br />
<button disabled="@loading" class="btn btn-primary" onclick="AddUser">
@if (loading)
{
<span class="spinner-border spinner-border-sm mr-1"></span>
<NavLink href="/login" class="btn btn-link">Register</NavLink>
}
Register
</button>
<NavLink href="/login" class="btn btn-link">Login</NavLink>
</EditForm>
@code {
private User _user = new User();
private string StatusMessage;
private string StatusClass;
private bool loading;
private readonly AppDbContext _dataContext; //warning this record: Field Register._dataContext is never assigned to, and will always have its default value null.
//provjeriti: var context = new SchoolContext()
private void OnValidSubmit()
{
if (loading == true)
{
Console.WriteLine("You have successfully registered!");
}
else
{
loading = false;
Console.WriteLine("Check your information again!");
}
}
//protected void HandleValidSubmit()
//{
// StatusClass = "alert-info";
// StatusMessage = " You have successfully registered! Please click the Login button to log in!";
@*}*@
private async void HandleValidSubmit()
{
try
{
_dataContext.User.Add(_user); //error in this record System.NullReferenceException: 'Object reference not set to an instance of an object.' <> 4__this._dataContext was null.
await _dataContext.SaveChangesAsync();
}
catch
{
base.StateHasChanged();
}
_user = new User();
base.StateHasChanged();
}
protected void HandleInvalidSubmit()
{
StatusClass = "alert-danger";
StatusMessage = " Check your information again!";
}
//public bool doesCompanyExist(string Company)
//{
// User u = new User();
// if (u.IsValid(Company))
// return true;
// else
// return false;
//}
}
用户.cs:
using FluentValidation;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Data.SqlClient;
using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.ComponentModel.DataAnnotations.Schema;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using TestBlazor.Data;
namespace TestBlazor.Models
{
[Table("Users")]
public class User
{
[Display(AutoGenerateField = false)]
public int UserId { get; set; }
[Display(Name = "UserName")]
[Required(ErrorMessage = "UserName is required.")]
public string UserName { get; set; }
[Display(Name = "Password")]
[Required]
[MinLength(8, ErrorMessage = "password must be atleast 8 characters")]
[DataType(DataType.Password)]
public string Password { get; set; }
[Display(Name = "Email")]
[Required(ErrorMessage = "Email is required.")]
public string Email { get; set; }
[Display(Name = "Company")]
[StringLength(255)]
[Required(ErrorMessage = "Company is required.")]
[Remote("doesCompanyExist", "Company", HttpMethod = "POST", ErrorMessage = "Company already exists. Please enter a different company.")]
public string Company { get; set; }
public User GetRegisteredUser()
{
return new User
{
UserName = UserName,
Password = Password,
Email = Email,
Company = Company,
};
}
}
}
AppDbContext.cs:
using Microsoft.EntityFrameworkCore;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using TestBlazor.Models;
namespace TestBlazor.Data
{
public class AppDbContext : DbContext
{
public AppDbContext()
{
}
public AppDbContext(DbContextOptions<AppDbContext> options) : base(options)
{
}
protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
{
if (!optionsBuilder.IsConfigured)
{
optionsBuilder.UseSqlServer("Data Source=(LocalDb)\\MSSQLLocalDB;Initial Catalog=testblazor;Integrated Security=True;");
}
}
//protected override void OnModelCreating(ModelBuilder modelBuilder)
//{
// base.OnModelCreating(modelBuilder);
// modelBuilder.Entity<User>()
//}
public DbSet<User> User { get; set; }
public DbSet<Item> Items { get; set; }
}
}
解决方案
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