访问对象数组-运行时 System.NullReferenceException [重复]

Posted 2023-04-13

【中文标题】访问对象数组-运行时 System.NullReferenceException [重复]

【英文标题】：Access an Object Array - System.NullReferenceException during runtime [duplicate]

【发布时间】：2019-12-28 04:54:14

【问题描述】：

我是 C# 新手，我的编码有问题。我在运行时出错。似乎没有分配对象数组。欢迎任何帮助/提示。我有一个带固定房间的“建筑”类。预计不会有任何变化或额外的房间。 房间有很多属性。在我的“家庭”课程中，我想通过对象数组和特定房间访问所有房间。 提前致谢：

Class Home

private void StartProgramm()
        

            //get all Objects of class "Building"
            Building[] building = Building.Buildings;

            //System.NullReferenceException during runtime

            set_label_header(building[0].Name);

            //Access to room1
            Building room1 = Building.room1;

            set_label_header(room1.Name);

            //Get room2
            Building room2 = Building.GetBuilding("room2");

            set_label_header(room2?.Name);



         



    class Building
    

        public string Name  get; set; 
        public ArrayList tool_groupList = new ArrayList();
        public ArrayList pos_List = new ArrayList();
        public ArrayList inv_list = new ArrayList();


        public static Building room1;
        public static Building room2;
        public static Building[] Buildings;


    public Building()
            
            //create room 1 and add some attributes
            room1 = new Building  Name = "room1" ;
            room1.tool_groupList.Add(1);
            room1.tool_groupList.Add(2);
            room1.pos_List.Add(14);
            room1.pos_List.Add(15);
            room1.pos_List.Add(16);
            room1.pos_List.Add(17);
            Iventory[] inventories = Inventory.get_inventories();
            room1.areaList.AddRange(inventories);



            //create room 2 and add some attributes
            room2 = new Building  Name = "room2" ;
            room2.tool_groupList.Add(2);
            room2.pos_List.Add(1);
            room2.pos_List.Add(2);
            room2.pos_List.Add(9);
            room2.pos_List.Add(10);
            room2.pos_List.Add(13);
            room2.pos_List.Add(14);
            room2.pos_List.Add(15);
            room2.pos_List.Add(16);
            Iventory[] inventories = Inventory.get_inventories();
            room2.areaList.AddRange(inventories);


            //Array with all rooms
            Buildings = new Building[]  room1, room2 ;


        

        //get single room by name

        public static Building GetBuilding(string name)
        
            foreach (Building Building in Buildings)
            
               if( Building.Name != null && Building.Name.Equals(name, StringComparison.OrdinalIgnoreCase))
                
                    return Building;
                

            
            return null;
        





    

【问题讨论】：

您能帮我们找出错误所在的确切行吗？

set_label_header(building[0].Name);

好吧，我最好的猜测是当您尝试访问building[0] 时building 为空。既然building不存在，那么它就不能给你building[0]。你有没有在调试模式下跳过代码？

【参考方案1】：

您正试图在调用 Building 类的构造函数之前访问静态字段 Building.Buildings。创建Building 的实例后，将分配静态字段。您可能希望使用如下示例中的静态构造函数：

static Building()

    ...
    Buildings = new Building[]  room1, room2 ;

【讨论】：

谢谢，这就是解决方案