Question

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

using System.IO;
using System.Runtime.Serialization.Formatters.Binary;

namespace FoolballLeague
{
    public partial class MainMenu : Form
    {
        FootballLeagueDatabase footballLeagueDatabase;
        Game game;
        Login login;

        public MainMenu()
        {
            InitializeComponent();
            changePanel(1);
        }

        public MainMenu(FootballLeagueDatabase footballLeagueDatabaseIn)
        {
            InitializeComponent();
            footballLeagueDatabase = footballLeagueDatabaseIn;
        }

        private void Form_Loaded(object sender, EventArgs e)
        {
        }



        private void gameButton_Click(object sender, EventArgs e)
        {
            int option = 0;
            changePanel(option);
        }
        private void scoreboardButton_Click(object sender, EventArgs e)
        {
            int option = 1;
            changePanel(option);
        }
        private void changePanel(int optionIn)
        {
            gamePanel.Hide();
            scoreboardPanel.Hide();

            string title = "Football League System";

            switch (optionIn)
            {
                case 0:
                    gamePanel.Show();
                    this.Text = title + " - Game Menu";
                    break;
                case 1:
                    scoreboardPanel.Show();
                    this.Text = title + " - Display Menu";
                    break;
            }
        }

        private void logoutButton_Click(object sender, EventArgs e)
        {
            login = new Login();
            login.Show();
            this.Hide();
        }

        private void addGameButton_Click(object sender, EventArgs e)
        {
            if ((homeTeamTxt.Text.Length) == 0)
                MessageBox.Show("You must enter a Home Team");
            else if (homeScoreUpDown.Value > 9 || homeScoreUpDown.Minimum < 0)
                MessageBox.Show("You must enter one digit between 0 and 9");
            else if ((awayTeamTxt.Text.Length) == 0)
                MessageBox.Show("You must enter a Away Team");
            else if (homeScoreUpDown.Value > 9 || homeScoreUpDown.Value < 0)
                MessageBox.Show("You must enter one digit between 0 to 9");
            else 
            {
                //checkGameInputFields();
                game = new Game(homeTeamTxt.Text, int.Parse(homeScoreUpDown.Value.ToString()), awayTeamTxt.Text, int.Parse(awayScoreUpDown.Value.ToString()));
                MessageBox.Show("Home Team -" + '\t' + homeTeamTxt.Text + '\t' + "and" + '\r' + "Away Team -" + '\t' + awayTeamTxt.Text + '\t' + "created");
                footballLeagueDatabase.AddGame(game);

                //clearCreateStudentInputFields();
            }
        }
        private void timer1_Tick(object sender, EventArgs e)
        {
            displayDateAndTime();
        }

        private void displayDateAndTime()
        {
            dateLabel.Text = DateTime.Today.ToLongDateString();
            timeLabel.Text = DateTime.Now.ToShortTimeString();
        }

        private void displayResultsButton_Click(object sender, EventArgs e)
        {
            Game game = new Game(homeTeamTxt.Text, int.Parse(homeScoreUpDown.Value.ToString()), awayTeamTxt.Text, int.Parse(awayScoreUpDown.Value.ToString()));

            gameResultsListView.Items.Clear();
            gameResultsListView.View = View.Details;

            ListViewItem row = new ListViewItem();
            row.SubItems.Add(game.HomeTeam.ToString());
            row.SubItems.Add(game.HomeScore.ToString());
            row.SubItems.Add(game.AwayTeam.ToString());
            row.SubItems.Add(game.AwayScore.ToString());

            gameResultsListView.Items.Add(row);
        }

        private void displayGamesButton_Click(object sender, EventArgs e)
        {
            Game game = new Game("Home", 2, "Away", 4);//homeTeamTxt.Text, int.Parse(homeScoreUpDown.Value.ToString()), awayTeamTxt.Text, int.Parse(awayScoreUpDown.Value.ToString()));

            modifyGamesListView.Items.Clear();
            modifyGamesListView.View = View.Details;

            ListViewItem row = new ListViewItem();
            row.SubItems.Add(game.HomeTeam.ToString());
            row.SubItems.Add(game.HomeScore.ToString());
            row.SubItems.Add(game.AwayTeam.ToString());
            row.SubItems.Add(game.AwayScore.ToString());

            modifyGamesListView.Items.Add(row);
        }

       }
    }

这是整个代码，我得到的问题与上一个问题相同。

你身上发生了未处理的异常应用。如果你点击...............点击退出申请将立即关闭。对象引用未设置为对象的实例。

以下详细信息在错误消息中。

**************异常文本************** System.NullReferenceException：Object 引用未设置为的实例宾语。在 FoolballLeague.MainMenu.addGameButton_Click（对象发件人，EventArgs e）in C：\用户\ achini \桌面\ FootballLeague \ FootballLeague \ MainMenu.cs：行 91点 System.Windows.Forms.Control.OnClick（EventArgs的吃 System.Windows.Forms.Button.OnMouseUp（MouseEventArgs mevent）at System.Windows.Forms.Control.WmMouseUp（消息＆安培; m，MouseButtons按钮，Int32点击）在 System.Windows.Forms.Control.WndProc（消息＆安培; m）at System.Windows.Forms.ButtonBase.WndProc（消息＆安培; m）at System.Windows.Forms.Button.WndProc（消息＆安培; m）at System.Windows.Forms.Control.ControlNativeWindow.WndProc（消息＆安培; m）at System.Windows.Forms.NativeWindow.Callback（IntPtr的 hWnd，Int32 msg，IntPtr wparam，IntPtr LPARAM）

我需要添加游戏以使用addGameButton并保存这些添加的游戏并将其显示在列表视图中（gameResultsListView）。现在我可以添加一个游戏并在列表视图中显示。但是当我按下addGameButton按钮时，我收到了上面的错误信息。

如果可以，请为我解决这个问题。

Answer 1

从异常消息中我可以看到你在第91行的addGameButton_Click中有一个NullReferenceException。这是第91行：

footballLeagueDatabase.AddGame(game);

所以footballLeagueDatabase为null。让我们看看你分配给它的代码：

public MainMenu()
{
    InitializeComponent();
    changePanel(1);
}

public MainMenu(FootballLeagueDatabase footballLeagueDatabaseIn)
{
    InitializeComponent();
    footballLeagueDatabase = footballLeagueDatabaseIn;
}

我猜你要么调用错误的构造函数，要么将null对象传递给构造函数。

这是整个代码

不，这不是整个代码。您的项目中应该有其他一些文件。错误很可能出现在其中一个文件中（构造此表单的文件）。

Answer 2

您需要学习读取错误消息和堆栈跟踪。

看看这一点：

System.NullReferenceException: Object reference not set to an instance of an object. at FoolballLeague.MainMenu.addGameButton_Click(Object sender, EventArgs e) in C:\Users\achini\Desktop\FootballLeague\FootballLeague\MainMenu.cs:line 91

告诉你错误在哪一行。它还告诉你它是NullReferenceException，这意味着不应该是null。

设置一个断点，并逐步执行相关代码，检查变量会发生什么，并弄清楚它是如何以空值结束的。

Answer 3

您尝试访问的其中一个引用为null。它位于MainMenu.cs文件的第91行。设置断点并查看调试器，什么是null？

我猜想footballLeagueDatabase为null，你需要为它分配一个类型为FootballLeagueDatabase的实例。

Answer 4

你确定footballLeagueDatabase正在初始化吗？我认为初始化它的构造函数永远不会被调用。

Answer 5

看起来你似乎没有初始化footballLeagueDatabase任何地方

c＃中的异常错误

5 个答案: