Question

我正在努力学习C＃，我在书中遇到了一个问题。我无法弄清楚为什么它将我的Room objets Exit设置为适当的Loactions，但是我的RoomWithDoor.Exits为null。

    public Form1()
            {
                InitializeComponent();
                CreateObjects();
                MoveToANewLocation(livingRoom);
            }
            public void CreateObjects()
            {
                livingRoom = new RoomWithDoor("living room", "an antique carpet", "an oak door with a brass knob");
                livingRoom.Exits = new Locations[] { diningRoom, kitchen };
                livingRoom.DoorLocation = frontYard;

                diningRoom = new Room("dining room", "crystal chandelier");
                diningRoom.Exits = new Locations[] { livingRoom, kitchen };

    abstract class Locations
    {
        public Locations(string name)
        {
            this.name = name;
        }
        public Locations[] Exits;
        private string name;
        public string Name { get { return name; } }

class Room : Locations
{
    public Room(string name, string decoration)
        : base(name)
    {
        this.decoration = decoration;
    }
class RoomWithDoor : Room, IHasExteriorDoor
{
    public RoomWithDoor(string name, string decoration, string doorDescription)
        : base(name, decoration)
    {
        this.doorDescription = doorDescription;
    }

所以，这是有效的

private void MoveToANewLocation(Locations newLocation)
        {
    currentLocation = newLocation;
            currentLocationExit = currentLocation.Exits[0];
            MessageBox.Show(diningRoom.Name);

但这不是

    MessageBox.Show(livingRoom.Exits[0].Name);

Answer 1

livingRoom = new RoomWithDoor("living room", "an antique carpet", "an oak door with a brass knob");
livingRoom.Exits = new Locations[] { diningRoom, kitchen };
livingRoom.DoorLocation = frontYard;

diningRoom = new Room("dining room", "crystal chandelier");
diningRoom.Exits = new Locations[] { livingRoom, kitchen };

这不能按预期工作。由于您在分配diningRoom后为livingRoom.Exits分配了新值，livingRoom.Exits在分配时仍会保留值diningRoom，这可能是null }。

Answer 2

在餐厅初始化之前，您将餐厅添加到起居室的出口处......

创建餐厅和起居室，然后使用您创建的对象设置出口，否则它们将为null，因为您将出口设置为对空对象的引用，然后将餐厅参考设置为新对象

C＃继承似乎没有正常工作

2 个答案: