c# - 查询文本框时出错

Question

这应该是一个简单的解决方案，但 Visual Studio 2012 给我的错误提示是 sqlCon 是一个字段但被用作一个类型，对于 Textbox1 也是同样的错误...也许我缺少程序集引用或正确的连接导入？我希望继续这条简单的路线。

    MySqlConnection sqlCon = new MySqlConnection("Server=***;Port=***;Database=***;Uid=***;Pwd=***;");
    MySqlCommand commandText = new MySqlCommand ("SELECT count(Dues) From Students");
        sqlCon.CommandText = "SELECT * count(Dues) FROM Students";
        sqlCon.Connection = sqlCon;
        TextBox1.Text = sqlCon.ExecuteScalar().ToString();

Answer 1

• 打开连接
• 使用 using 语句
• 使用Try-catch block

片段，

string connStr = "Server=***;Port=***;Database=***;Uid=***;Pwd=***;";
string query = "SELECT count(Dues) From Students";
using(MySqlConnection sqlCon = new MySqlConnection(connStr))
{
    using(MySqlCommand sqlComm = new MySqlCommand())
    {
        sqlComm.Connection = sqlCon;
        sqlComm.CommandText = query;

        try
        {
            sqlCon.Open();
            TextBox1.Text = sqlComm.ExecuteScalar().ToString();
        }
        catch(MySqlException ex)
        {
            MessageBox.Show(ex.ToString());
        }
    }
}