问题就在这里。我正在尝试执行查询及其抛出和异常connection.Open。奇怪的是，在同一个应用程序上我正在执行“选择”查询并且它工作正常。但是当我执行“更新”查询时，它会抛出“无法连接到任何指定的 MySQL 主机”错误。一直卡在这上面。有人能发现我哪里出错了。
private void button1_Click(object sender, EventArgs e)
{
if (radioButton1.Checked)
{
timerEnabled = 1;
}
connection.Open();
//update the settings to the database table
MySqlCommand command = connection.CreateCommand();
command.CommandText = "update Admin_Settings set Difficulty='" + comboBox3.Text + "'," + "NoOfQuestions='" + comboBox4.Text + "'," + "NoOfChoices='" + comboBox5.Text + "'," +
"Subject='" + comboBox8.Text + "'," + "Timer='" + comboBox2.Text + "," + "TimerEnabled=" + timerEnabled + "," + "TimerType='" + comboBox1.Text + "'";
command.ExecuteNonQuery();
MessageBox.Show("Settings updated");
}
我将建议您执行以下操作：
private void button1_Click(object sender, EventArgs e)
{
using (System.Data.SqlClient.SqlConnection connection = new System.Data.SqlClient.SqlConnection(connString))
{
if (radioButton1.Checked)
{
timerEnabled = 1;
}
connection.Open();
//update the settings to the database table
MySqlCommand command = connection.CreateCommand();
command.CommandText = "update Admin_Settings set Difficulty='" + comboBox3.Text + "'," + "NoOfQuestions='" + comboBox4.Text + "'," + "NoOfChoices='" + comboBox5.Text + "'," +
"Subject='" + comboBox8.Text + "'," + "Timer='" + comboBox2.Text + "," + "TimerEnabled=" + timerEnabled + "," + "TimerType='" + comboBox1.Text + "'";
command.ExecuteNonQuery();
MessageBox.Show("Settings updated");
}
}
我知道您在想，您应该保持连接以方便使用，等等，但根据我的经验，这是浪费精力。最终发生的事情是很多你不想要或不需要的麻烦。您最终没有意识到您在其他地方打开了连接，并且您花费了数小时来排除不应该排除的问题。打开您的连接，完成后关闭它。
如果您想要一个连接对象，那很好，但请使用 using 模式，以便每次都会处理它，并且始终从连接开始。
注意：用 yoru MySqlConnection 对象替换我的连接！
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