C＃mysql数据库连接类对象错误

Question

我是C＃的新手，我只是使用mysql创建数据库连接。然后我需要在这里定义一个数据库连接类，这是我的代码

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using MySql.Data.MySqlClient;

namespace restsurant_pos
{
    class mysqlDbConnect
    {

          public static MySqlConnection GetConnection(){
            string MyConnectionString = "Server=Localhost;Database=pos;Uid=root;Pwd='';";
            MySqlConnection connection = new MySqlConnection(MyConnectionString);
            MySqlCommand cmd;
            connection.Open();

            return connection;

          }

希望它是正确的..

然后如何使用此类创建对象。我刚刚创建了如下所示，但它出现了错误。

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using MySql.Data.MySqlClient;

namespace restsurant_pos
{
    public partial class AddCategory : Form
    {

        public AddCategory()
        {
            InitializeComponent();
        }

        private void btn_insertCategory_Click(object sender, EventArgs e)
        {
            string categoryName = txtCategoryName.Text;

            mysqlDbConnect connection = new mysqlDbConnect();

            try
            {
                cmd = connection.CreateCommand();
                cmd.CommandText = "INSERT INTO categories(name) VALUES(@categoryName)";
                cmd.Parameters.AddWithValue("categoryName", txtCategoryName.Text);
                cmd.ExecuteNonQuery();
                this.Close();
            }
            catch (Exception)
            {
                throw;
            }

            finally 
            {
                if (connection.State == ConnectionState.Open) {
                    connection.Close();
                }
            }
        }
    }
}

我的代码有什么问题..请帮忙

Answer 1

您尚未为type提供cmd。

通过将其（懒惰地）声明为var cmd = connection.CreateCommand()或使用硬编码类型来解决它。