Question

这里的总菜鸟。这是我的第一次c＃尝试，它是一个控制器应用程序，模拟一个名为“左右中心”的饮酒游戏。在控制台中，我收到以下内容：

CONSOLE

Unhandled Exception: System.NullReferenceException: Object reference not set to an instance of an object
at LeftRightCenter.MainClass.Main (System.String[] args) [0x00038] in     /Users/apple/Projects/LearningC/LearningC/Main.cs:80 
[ERROR] FATAL UNHANDLED EXCEPTION: System.NullReferenceException: Object reference not set to an instance of an object
 at LeftRightCenter.MainClass.Main (System.String[] args) [0x00038] in /Users/apple/Projects/LearningC/LearningC/Main.cs:80

C＃

    using System;

    namespace LeftRightCenter
    {
        class Player
        {
            //fields        
            private int _quarters = 4;

            public int Quarters {
                get{ return _quarters; }
                set{ _quarters += value; }
            }

            public Player (string name)
            {

            }   

        }
        class Dice
        {
            Random random = new Random();
            public int Roll ()
            {
                random = new Random ();
                int diceSide;
                diceSide = random.Next (0, 6);
                diceSide = (diceSide > 2) ? 3 : diceSide;
                return diceSide;            
            }
        }
        class MainClass
        {
            static int activePlayer = 0;
            static int theCup       = 0;

            static Player[] thePlayers = { 
                new Player ("Jessica"), 
                new Player ("Isaac"), 
                new Player ("Ed"), 
                new Player ("Bella"),
                new Player ("Elisa"),
                new Player ("Fake RedHead"),
                new Player ("Linda"),
                new Player ("MJ"),
                new Player ("Irene"),
                new Player("Devin")
            };

            static Dice[] theDice = new Dice[2];

            private static void MoveQuarter (int direction)
            {
                int numberOfPlayers = thePlayers.Length - 1;
                switch (direction) {
                case 0: 
                    thePlayers [activePlayer].Quarters = -1;
                    theCup++;
                    break;
                case 1:
                    thePlayers [activePlayer].Quarters = -1;
                    int leftPlayer = (activePlayer == 0) ? numberOfPlayers : activePlayer - 1;
                    thePlayers [leftPlayer].Quarters = +1;
                    break;
                case 2:
                    thePlayers [activePlayer].Quarters = -1;
                    int rightPlayer = (activePlayer == numberOfPlayers) ? 0 : activePlayer + 1;
                    thePlayers [rightPlayer].Quarters = +1;
                    break;                          
                }           
            }

            public static void Main (string[] args)
            {
                int cupEndPoint = thePlayers.Length * 4 - 1;
                while (theCup < cupEndPoint) {
                    foreach (Dice rattle in theDice) {
                        if (thePlayers [activePlayer].Quarters > 0) {
                            MoveQuarter (rattle.Roll ()); // this line seems to be the problem  
                        }                   
                    }
                    Console.WriteLine ("{0} Quarters In the Cup", theCup);
                }

            }
        }
    }

我不知道问题是什么或为什么，我的谷歌搜索已被证明更多使用混乱而不是有用。

对于那些好奇的人，我现在几乎没有实验工作

http://pastebin.com/jxCCW2cd

Answer 1

这一行

static Dice[] theDice = new Dice[2];

声明一个允许存储Dice类的2个对象的数组，但此数组中的每个值仍为null。

在Main方法中的foreach循环中使用它之前，需要在数组的每个插槽上创建一个Dice。

theDice[0] = new Dice();
theDice[1] = new Dice();

如果您在行

上停止调试器

 MoveQuarter (rattle.Roll ());

你会看到rattle骰子为空。

编辑：看看你的代码，我发现了一些有问题的情况在Roll方法中，您重新创建Random生成器，这对随机性没有好处。 (See the accepted answer in this question)
最后，可以使用与已经为thePlayers数组

相同的方式创建和初始化Dice数组

static Dice[] theDice = new Dice[2] {new Dice(), new Dice()};

这是您的Dice类的完整修订

class Dice 
{
    private static Random random;
    public  Dice()
    {
           // create the static random generator only on the first instance
        if(random == null) random = new Random();
    }

    public int Roll () 
    { 
        int diceSide; 
        diceSide = random.Next (1, 7); 
        diceSide = (diceSide > 2) ? 3 : diceSide; 
        return diceSide;             
    } 
}

我的第一个c＃app和第一个null对象异常

1 个答案: