Question

我有两个派生自同一基类的类

public class AugInfo
{
    public string UserId { get; set; }
    public string Email { get; set; }
    public bool EmailConfirmed { get; set; }
    public string PhoneNumber { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Name { get { return FirstName + " " + LastName; } }
    public string Company { get; set; }
    public string City { get; set; }
    public string State { get; set; }
    public Boolean LockedOut { get; set; }

    public string Country { get; set; }
    public int ModelsCount { get; set; }
    public DateTime CreateDate { get; set; }
    public string LoginProvider { get; set; }

    public AugInfo() { }

}

public class AdminUserInfo : AugInfo
public class GroupUserInfo : AugInfo

下面描述了两个函数

    protected List<AdminUserInfo> FilterUsers(List<AdminUserInfo> users,SearchViewModel<AdminUserInfo, EnumUserSort> search)
    {
        if (!string.IsNullOrEmpty(search.SearchString))
        {
            users = users.Where(d => 
             d.Email.ToLower().Contains(search.SearchString.ToLower())
                  || d.Name.ToString().Contains(search.SearchString) ||
                  d.Company.ToString().ToLower().Contains(search.SearchString.ToLower())).ToList();
        }
        return users;
    }


 protected List<GroupUserInfo> FilterUsers(List<GroupUserInfo> users,SearchViewModel<GroupUserInfo, EnumUserSort> search)
    {
        if (!string.IsNullOrEmpty(search.SearchString))
        {
            users = users.Where(d => d.Email.ToLower().Contains(search.SearchString.ToLower())
              || d.Name.ToString().Contains(search.SearchString) ||
              d.Company.ToString().ToLower().Contains(search.SearchString.ToLower())).ToList();
        }
        return users;
    }

在这个函数中，我只使用那些属于AugInfo的属性。我有一种方法可以使用Polymorphism或Generic types将它们组合成一个函数。我无法做到这一点。

我试图声明一个像这样的函数

    protected List<AugInfo> FilterUsers(List<AugInfo> users,SearchViewModel<AugInfo, EnumUserSort> search)
    {
        if (!string.IsNullOrEmpty(search.SearchString))
        {
            users = users.Where(d => d.Email.ToLower().Contains(search.SearchString.ToLower())
                  || d.Name.ToString().Contains(search.SearchString) ||
                  d.Company.ToString().ToLower().Contains(search.SearchString.ToLower())).ToList();
        }
        return users;
    }

但不幸的是我无法调用该功能

 List<AdminUserInfo> users= FilterUsers(users, search);

我收到了会员错误

Answer 1

您需要T上的egeneric约束，以便只有从AugInfo派生的类型才能用作通用参数：

protected List<T> FilterUsers<T>(List<T> users, SearchViewModel<T, EnumUserSort> search) where T: AugInfo
{
    if (!string.IsNullOrEmpty(search.SearchString))
    {
        users = users.Where(d => 
            d.Email.ToLower().Contains(search.SearchString.ToLower())
                || d.Name.ToString().Contains(search.SearchString) 
                || d.Company.ToString().ToLower().Contains(search.SearchString.ToLower())).ToList();
    }
    return users;
}

Answer 2

应该在这里使用泛型：

protected List<T> FilterUsers<T>(List<T> users, SearchViewModel<T, EnumUserSort> search) where T : AugInfo {
    if (!string.IsNullOrEmpty(search.SearchString)) {
        users = users.Where(d =>
         d.Email.ToLower().Contains(search.SearchString.ToLower())
              || d.Name.ToString().Contains(search.SearchString) ||
              d.Company.ToString().ToLower().Contains(search.SearchString.ToLower())).ToList();
    }
    return users;
}

仅仅写List<AugInfo>是不够的，因为List<T>不是逆变和协变的同时（C＃中不存在这种情况）。您无法将List<BaseType>转换为List<DerivedType>。

多态性不理解

2 个答案: