如何使用C#通过超类的引用访问子类变量

Question

I have a User class which is my parent class. and I have a SiteAdmin class which is inherited from User class:

public abstract class User { }
public class SiteAdmin : User 
{
   public string ProfilePicUrl { get; set; }
}

The scenario is I want to check if an User instance is a type of SiteAdmin class, then access to SiteAdmin properties with User object. Suppose ProfilePicUrl is a property of SiteAdmin class. How can I access this propery with User object?

if (comment.User is SiteAdmin)
{
   var profilePicUrl = comment.User.ProfilePicUrl;
}

Answer 1

Try this:

if (comment.User is SiteAdmin siteAdmin)
{
    var profilePicUrl = siteAdmin.ProfilePicUrl;
}

Or you could do this:

if (comment.User is SiteAdmin)
{
    var profilePicUrl = (comment.User as SiteAdmin).ProfilePicUrl;
}

Answer 2

您可以定义超类和子类之间的契约，例如抽象方法，在User和SiteAdmin实现抽象方法并返回ProfilePicUrl 。