public class ParentClass    {       public ParentClass()       {        }       public string NamePropety { get; set; }       public void GetName()       {        }    } public class ChildClass:ParentClass    {       public ChildClass()       {        }       public int Age { get; set; }       public int GetAge()       {           return 10;       }    } ParentClass parent = new ParentClass();            //parent.NamePropety            //parent.GetName();            //子类转父类。            //ParentClass parent1 = new ChildClass(); 或者ParentClass parent1 = new ChildClass() as ParentClass;            //parent1.NamePropety            //parent1.GetName();            ChildClass child = new ChildClass();            //child.NamePropety            //child.GetName();            //child.GetAge();            //child.Age;            //父类转子类。            //child1为NUll对象。            //ChildClass child1 = new ParentClass() as ChildClass;  或者 ChildClass child1 = (ChildClass)new ParentClass();            //Console.WriteLine(child1.NamePropety);              //child1.GetName();            //child1.GetAge();            //child1.Age;