无法从接口转换为类

Question

当我尝试将我的界面添加到数据库时，我的方法出现错误，它给了我错误，

参数 1：无法从“ForumSite.ActionsAndMethods.Registration.IRegistration”转换为“ForumSite.Models.User”。

这是IRegistration中的代码：

 using ForumSite.Models;
 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
 using System.Threading.Tasks;

namespace ForumSite.ActionsAndMethods.Registration
{
public interface IRegistration
{
    int UserId { get; }
    string Email { get; }
    string Password { get; }
    string FirstName { get; }
    string LastName { get; }
    DateTime Birthday { get; }
    DateTime DateCreated { get; set; }
    string MobileNumber { get; }
    string Address { get; }
    int UserIsDeleted { get; set; }
    int UserRoleId { get; set; }
    UserRole UserRole { get; }
}
}

这是我模型中的代码：

namespace ForumSite.Models
{
using ActionsAndMethods.Registration;
using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;

public partial class User : IRegistration
{
    public int UserId { get; set; }
    [Display(Name = "Email Address")]
    [Required(ErrorMessage = "This field required.")]
    [RegularExpression(@"^([a-zA-Z0-9_\-\.]+)@([a-zA-Z]+)\.([a-zA-Z]{2,5})$", ErrorMessage = "Enter Valid Email Address")]
    [StringLength(50, MinimumLength = 8, ErrorMessage = "8 to 50 characters only")]
    public string Email { get; set; }

    [Display(Name = "Password")]
    [Required(ErrorMessage = "This field required.")]
    [RegularExpression(@"^[a-zA-Z0-9]+$", ErrorMessage = "Alphanumeric characters only")]
    [StringLength(50, MinimumLength = 8, ErrorMessage = "8 to 50 characters only")]
    public string Password { get; set; }

    [Display(Name = "Confirm Password")]
    [Required(ErrorMessage = "This field required.")]
    [RegularExpression(@"^[a-zA-Z0-9]+$", ErrorMessage = "Alphanumeric characters only")]
    [StringLength(50, MinimumLength = 8, ErrorMessage = "8 to 50 characters only")]
    public string PasswordConfirm { get; set; }

    [Display(Name = "First Name")]
    [Required(ErrorMessage = "This field required.")]
    [RegularExpression(@"^[a-zA-Z\s]+$", ErrorMessage = "Letters Only.")]
    public string FirstName { get; set; }

    [Display(Name = "Last Name")]
    [Required(ErrorMessage = "This field required.")]
    [RegularExpression(@"^[a-zA-Z\s]+$", ErrorMessage = "Letters Only.")]
    public string LastName { get; set; }

    [Display(Name = "Birthday")]
    [Required(ErrorMessage = "This field required.")]
    public DateTime Birthday { get; set; }
    public DateTime DateCreated { get; set; }

    [Display(Name = "Mobile Number")]
    [Required(ErrorMessage = "This field required.")]
    [RegularExpression(@"^[0-9]+$", ErrorMessage = "Numeric input only.")]
    public string MobileNumber { get; set; }

    [Display(Name = "Address")]
    [Required(ErrorMessage = "This field required.")]
    public string Address { get; set; }
    public int UserIsDeleted { get; set; }
    public int UserRoleId { get; set; }

    public UserRole UserRole { get; set; }
}
}

最后，我将用户添加到我的数据库的方法：

using ForumSite.ActionsAndMethods.Registration;
using ForumSite.Models;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace ForumSite.ActionsAndMethods
{
public class RegisterAction : IRegistration
{
    ForumDBEntities ent = new ForumDBEntities();
    public void Registration(IRegistration reg)
    {
        reg.DateCreated = DateTime.Now;
        reg.UserRoleId = 1;
        reg.UserIsDeleted = 0;

        ent.Users.Add(reg);
        ent.SaveChanges();
    }

    string IRegistration.Address { get; }
    int IRegistration.UserId { get; }
    string IRegistration.Email { get; }
    string IRegistration.Password { get; }
    string IRegistration.FirstName { get; }
    string IRegistration.LastName { get; }
    DateTime IRegistration.Birthday { get; }
    DateTime IRegistration.DateCreated { get; set; }
    string IRegistration.MobileNumber { get; }
    int IRegistration.UserIsDeleted { get; set; }
    int IRegistration.UserRoleId { get; set; }

    UserRole IRegistration.UserRole { get; }
}

}

我想知道是什么导致了这个错误？

Answer 1

虽然每个User 都实现IRegistration，但并不是每个IRegistration 实例都是User。

例如，您的RegisterAction 也实现了IRegistration。所以如果你想做的事情是可能的，理论上你可以有这个代码：

RegisterAction action = GetRegisterAction();

RegisterAction action2 = new RegisterAction(action);

这意味着当你来做：

ent.Users.Add(reg);

它将失败，因为reg 不是User。

你可以这样解决它：

var user = reg as User;
if(user != null)
{
    ent.Users.Add(user);
}

但实际上你应该先看看你的结构，因为这样做似乎很奇怪。

Answer 2

你还没有告诉你得到编译错误的确切位置，但我的猜测是它在 Registration 方法中的 ent.Users.Add(reg) 行中。

要修复编译错误，您应该将Registration 方法的参数从IRegistration 更改为User：

public void Registration(User reg)
{
    reg.DateCreated = DateTime.Now;
    reg.UserRoleId = 1;
    reg.UserIsDeleted = 0;

    ent.Users.Add(reg);
    ent.SaveChanges();
}

但是，如果您尝试将 IRegistration 而不是 User 传递给 Registration 方法，这可能会在调用链的上游触发另一个编译错误。

虽然User 可以（并且确实）实现了IRegistration，但您不能假设任何实现IRegistration 的东西都是User。如果您的代码基于该假设，您将不得不修复它以解决您的问题。