系统建立连接失败

Question

我正在pos系统上工作，一切正常。我已经在服务器资源管理器的Visual Studio中添加了MySQL数据库。

但是当我尝试通过数据库连接来连接软件时，却出现了错误：

  

系统无法建立连接

请向我指出我错了，什么是解决此问题的最佳方法：

    private string TstServerMySQL;
    private string TstPortMySQL;
    private string TstUserNameMySQL;
    private string TstPwdMySQL;
    private string TstDBNameMySQL;

    private void cmdTest_Click(object sender, EventArgs e)
    {
        //Test database connection

        TstServerMySQL = txtServerHost.Text;
        TstPortMySQL = txtPort.Text;
        TstUserNameMySQL = txtUserName.Text;
        TstPwdMySQL = txtPassword.Text;
        TstDBNameMySQL = txtDatabase.Text;

        try
        {
            SQLConn.conn.ConnectionString = "Server = '" + TstServerMySQL + "';  " + "Port = '" + TstPortMySQL + "';" + "user id = '" + TstUserNameMySQL + "';   " + "password = '" + TstPwdMySQL + "'; " + "Database = '" + TstDBNameMySQL + "'";
            SQLConn.conn.Open();
            Interaction.MsgBox("Test connection successful", MsgBoxStyle.Information, "Database Settings");

        }
        catch
        { 
            Interaction.MsgBox("The system failed to establish a connection", MsgBoxStyle.Information, "Database Settings");
        }
        SQLConn.DisconnMy();
    }