对象数组中的 NullReferenceException

Question

我正在用 c# 开发一个程序，其中我有一个 class 的对象数组。我在 class 中有一个构造函数，它应该为附加的字符串赋值 "" 以确保它们为空，以便可以轻松传递信息。然后我像这样创建了数组：

participants[8][8] grid = new participants[8][];

但是我被抛出 NullReferenceExcetption 错误。这是我的代码供您参考。

using System;

namespace TreasurehuntCsharp
{
    class square
    {
        public string strX = "";
        public int y = 0;
        public int x = 0;
    }

    class participants
    {
        public string name = "";
        public string contact = "";
        public participants()
        {
            name = "";
            contact = "";
        }
    }

    class Program
    {

        //Method for user to choose a square
        static void Input(square Coord)
        {
            //Variables
            bool correct = false;

            //Inputs

            Console.WriteLine("Please enter the coordinates of the square you would like to select: \r\n");

            do
            {
                //X coordinate
                Console.WriteLine("X: ");
                Coord.strX = Console.ReadLine().ToLower();
                //Convert letter to array coordinate
                switch (Coord.strX)
                {
                    case "a":
                        Coord.x = 0;
                        correct = true;
                        break;
                    case "b":
                        Coord.x = 1;
                        correct = true;
                        break;
                    case "c":
                        Coord.x = 2;
                        correct = true;
                        break;
                    case "d":
                        Coord.x = 3;
                        correct = true;
                        break;
                    case "e":
                        Coord.x = 4;
                        correct = true;
                        break;
                    case "f":
                        Coord.x = 5;
                        correct = true;
                        break;
                    case "g":
                        Coord.x = 6;
                        correct = true;
                        break;
                    case "h":
                        Coord.x = 7;
                        correct = true;
                        break;
                    default:
                        Console.WriteLine("Please enter a letter from A to H");
                        correct = false;
                        break;
                }
            } while (correct != true);

            correct = false;

            do
            {
                //Y coordinate
                Console.WriteLine("Y: ");
                Coord.y = Convert.ToInt32(Console.ReadLine());
                if (Coord.y >= 1 && Coord.y <= 7)
                {
                    correct = true;
                }
                else
                {
                    Console.WriteLine("Please input an integer value from 1 to 7.");
                    correct = false;
                }
            } while (correct != true);
        }

        static void ParticipantDetails(participants User)
        {
            Console.WriteLine("Please input your name and Contact number: ");
            
            //User name input
            Console.WriteLine("Name: ");
            User.name = Console.ReadLine();

            //User contact number input
            Console.WriteLine("Number: ");
            User.contact = Console.ReadLine();
        }

        static void Main(string[] args)
        {
            //Objects
            square Coord = new square();
            participants User = new participants();

            //Initialise 2D array
            participants[][] grid = new participants[8][];

            //Variables
            bool correct = false;

            do
            {
                //Methods
                Input(Coord);
                ParticipantDetails(User);

                //Input data to array
                if (grid[Coord.x][Coord.y].name == "" && grid[Coord.x][Coord.y].contact == "")
                {
                    grid[Coord.x][Coord.y].name = User.name;
                    grid[Coord.x][Coord.y].contact = User.contact;
                    Console.WriteLine(grid[Coord.x][Coord.y]);
                    correct = true;
                }
                else
                {
                    Console.WriteLine("That square is already filled. Please try again.");
                    correct = false;
                }
            } while (correct == false);
        }
    }

Answer 1

您没有初始化数组的所有维度。

//Initialise 2D jagged array
participants[][] grid = new participants[8][];

// You can do that in a for loop
grid[0] = new participants[8];
grid[1] = new participants[8];
grid[2] = new participants[8];
...
grid[7] = new participants[8];

// For 循环等价物

for (int i = 0; i < grid.Length; i++) 
{
    grid[i] = new participant[8];
}

对你的情况更好的方法（因为所有的子数组有相同数量的元素），将使用 multidimensional-arrays

participants[,] grid = new participants[8,8];

// and access like this
grid[Coord.x, Coord.y]

Answer 2

您创建了一个数组数组。

 participants[][] grid = new participants[8][];

这是一个有8个条目的数组。每个条目都应该是一组参与者，但尚未创建。

你需要做的是创建8个数组并将它们分配给网格数组的元素。

        participant[][] grid = new participant[8][];
        for (int i = 0; i < grid.Length; i++)
            grid[i] = new participant[8];

这里我假设网格数组的每个元素也将包含 8 个元素，但这取决于您。

对象数组中的 NullReferenceException

NullReferenceException in array of objects

.net

c#

arrays

oop

nullreferenceexception