2

我正在为名为 OTServer 的游戏服务器编写数据库管理器，但我第二次使用 executereader() 时遇到问题。这是代码：

    private void button1_Click(object sender, EventArgs e)
    {
        Form1 f = new Form1();
        MySqlConnection conn = new MySqlConnection();
        conn.ConnectionString = "Server=" + f.GetText1().Text + ";Username=" + f.GetText2().Text + ";Pwd=" + f.GetText3().Text + ";Database=" + f.GetText4().Text + ";";
        conn.Open();
        MySqlCommand cmd = new MySqlCommand("SELECT * FROM `players` WHERE name = @Name", conn);
        cmd.Parameters.AddWithValue("@Name", textBox1.Text);

        MySqlDataReader Reader = cmd.ExecuteReader(CommandBehavior.SingleRow);
        while (Reader.Read())
        {
            label7.Text = (string)Reader[1];
            label7.Show();
            label8.Text = Reader[5].ToString();
            label8.Show();
            if ((int)Reader[6] == 1)
            {
                label9.Text = "Sorcerer (1)";
            }
            if ((int)Reader[6] == 2)
            {
                label9.Text = "Druid (2)";
            }
            if ((int)Reader[6] == 3)
            {
                label9.Text = "Paladin (3)";
            }
            if ((int)Reader[6] == 4)
            {
                label9.Text = "Knight (4)";
            }

            if ((int)Reader[6] == 0)
            {
                label9.Text = "None (0)";
            }
            label9.Show();

            if ((int)Reader[3] == 1)
            {
                label10.Text = "Player";
            }

            if ((int)Reader[3] == 2)
            {
                label10.Text = "Tutor";
            }

            if ((int)Reader[3] == 3)
            {
                label10.Text = "Senior Tutor";
            }

            if ((int)Reader[3] == 4)
            {
                label10.Text = "Gamemaster";
            }

            if ((int)Reader[3] == 5)
            {
                label10.Text = "Community Manager";
            }

            if ((int)Reader[3] == 6)
            {
                label10.Text = "God";
            }

            if ((int)Reader[3] < 1 || (int)Reader[3] > 6)
            {
                label10.Text = "Unknown";
            }

            label10.Show();

            label13.Text = "Account: " + Reader[4].ToString();
            label13.Show();
        }
        Reader.Close();

        cmd = new MySqlCommand("SELECT * FROM accounts WHERE id = @Account_ID", conn);
        cmd.Parameters.AddWithValue("@Account_ID", label13.Text);
        Reader = cmd.ExecuteReader(CommandBehavior.SingleRow);

        while (Reader.Read())
        {
            label11.Text = (string)Reader[0];
            label11.Show();
        }
        Reader.Close();
    }
4

2 回答 2

4

建议的解决方案：尝试using在你的周围放置一个块DataReader，或调用Dispose它：

using (DataReader Reader = cmd.ExecuteReader(CommandBehavior.SingleRow))
{
    // ...do something with your data reader... then finish by:
    Reader.Close();
}  // <-- Reader.Dispose() called automatically at the end of using block.

// ...prepare second command...

// the same again for the second command:
using (DataReader Reader = cmd.ExecuteReader(CommandBehavior.SingleRow))
{
    // ...
    Reader.Close();
}

假设您的问题的原因：数据库连接对象可能会进行一些内部簿记以跟踪数据读取器。我在类似的情况下发现一次只允许你DataReader一个。Close所以我相信你的代码的问题是，虽然你Reader没有明确地Disposed 它，所以连接对象认为当你执行第二个数据读取器时第一个数据读取器仍在使用中。

此外......为什么不简化这段代码：

        if ((int)Reader[6] == 1)
        {
            label9.Text = "Sorcerer (1)";
        }
        if ((int)Reader[6] == 2)
        {
            label9.Text = "Druid (2)";
        }
        ...

发表switch声明？：

        int x = (int)(Reader[6]);
        string label9Text = string.Empty;

        switch (x)
        {
            case 1:  label9Text = "Sorcerer (1)";  break;
            case 2:  label9Text = "Druid (2)";     break;
            ...
        }

        label9.Text = label9Text;

（这将为您节省大量重复输入。）

于 2010-11-21T14:25:28.130 回答
3

好吧，假设您的代码是正确的，您在执行代码中显示的两个阅读器时应该没有问题。也许您因为没有处理命令或其他原因而遇到问题。我推荐这样的方法（使用 Northwind db 制作的示例）：

using (SqlConnection connection = new SqlConnection("Data Source=.\\SQLEXPRESS;Initial Catalog=Northwind;Integrated Security=SSPI;"))
        {
            connection.Open();

            using (SqlCommand command = new SqlCommand("SELECT * FROM Orders", connection))
            {
                using (SqlDataReader reader = command.ExecuteReader(System.Data.CommandBehavior.SingleRow))
                {
                    while (reader.Read())
                    {
                        Console.WriteLine(reader.GetString(2));
                    }
                }
            }

            using (SqlCommand command = new SqlCommand("SELECT * FROM Products", connection))
            {
                using (SqlDataReader reader = command.ExecuteReader(System.Data.CommandBehavior.SingleRow))
                {
                    while (reader.Read())
                    {
                        Console.WriteLine(reader.GetString(1));
                    }
                }
            }
        }

在识别播放器类型时，您应该清理代码。而是创建一个枚举：

public enum PlayerType
{
    None = 0,
    Sorcerer = 1,
    Druid = 2,
    Paladin = 3
}

然后在阅读时执行以下操作：

PlayerType playerType = (PlayerType)reader.GetInt32(6);
label9.Text = playerType.ToString();
于 2010-11-21T14:31:35.153 回答