使標簽靜態錯誤：無法通過嵌套類型“windowsForm8.Form1.DBConnect”訪問外部類型“windowsForm8.Form1”的非靜態成員

Question

喲，這是我在這里的第一篇文章，我想知道如何在 C# 中解決這個問題，所以我嘗試連接到數據庫並從中選擇信息，這些信息將顯示為標簽！ 很簡單，所以這是我得到的錯誤：

無法通過嵌套類型“windowsForm8.Form1.DBConnect”訪問外部類型“windowsForm8.Form1”的非靜態成員

這是代碼：

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 WindowsFormsApplication8
{
public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();

    }

    public class DBConnect
    {

        private MySqlConnection connection;
        private string server;
        private string database;
        private string uid;
        private string password;


        //Constructor
        public DBConnect()
        {
            Initialize();
        }

        //Initialize values
        private void Initialize()
        {
            server = "net";
            database = "rainbow";
            uid = "ok";
            password = "passwd!";
            string connectionString;
            connectionString = "SERVER=" + server + ";" + "DATABASE=" +
            database + ";" + "UID=" + uid + ";" + "PASSWORD=" + password + ";";

            connection = new MySqlConnection(connectionString);
        }

        //open connection to database
        private bool OpenConnection()
        {

            try
            {
                connection.Open();
                return true;
            }
            catch (MySqlException ex)
            {
                //When handling errors, you can your application's response based 
                //on the error number.
                //The two most common error numbers when connecting are as follows:
                //0: Cannot connect to server.
                //1045: Invalid user name and/or password.
                switch (ex.Number)
                {
                    case 0:
                        MessageBox.Show("Cannot connect to server.  Contact administrator");
                        break;

                    case 1045:
                        MessageBox.Show("Invalid username/password, please try again");
                        break;
                    default :
                        MessageBox.Show("Connected Successfuly!!");
                        break;
                }
                return false;
            }


        }

        //Close connection
        private bool CloseConnection()
        {
            try
            {
                connection.Close();
                return true;
            }
            catch (MySqlException ex)
            {
                MessageBox.Show(ex.Message);
                return false;
            }
        }

        //Insert statement
        public void Insert()
        {
            string query = "INSERT INTO mytable (username, password) VALUES('shryder', 'nopassword')";

            //open connection
            if (this.OpenConnection() == true)
            {
                //create command and assign the query and connection from the constructor
                MySqlCommand cmd = new MySqlCommand(query, connection);

                //Execute command
                cmd.ExecuteNonQuery();

                //close connection
                this.CloseConnection();
            }
        }

        //Update statement
        public void Update()
        {
        }

        //Delete statement
        public void Delete()
        {

        }

        //Select statement
        public List<string>[] Select()
        {
            string query = "SELECT * FROM mytable";

            //Create a list to store the result
            List<string>[] list = new List<string>[3];
            list[0] = new List<string>();
            list[1] = new List<string>();
            list[2] = new List<string>();

            //Open connection
            if (this.OpenConnection() == true)
            {
                //Create Command
                MySqlCommand cmd = new MySqlCommand(query, connection);
                //Create a data reader and Execute the command
                MySqlDataReader dataReader = cmd.ExecuteReader();

                //Read the data and store them in the list
                if (dataReader.Read())
                {
                    /*list[0].Add(dataReader["username"] + "");
                    list[1].Add(dataReader["password"] + "");
                    list[2].Add(dataReader["email"] + "");*/
                    newscontent.Text = dataReader["username"]; //this is the error


                }

                //close Data Reader
                dataReader.Close();

                //close Connection
                this.CloseConnection();

                //return list to be displayed
                return list;
            }
            else
            {
                return list;
            }
        }

        //Count statement


        //Backup
        public void Backup()
        {
        }

        //Restore
        public void Restore()
        {
        }
    }



}
}

請幫助我，謝謝:)

Answer 1

將 DbConnect 類中的所有代碼移到 Form1 類中。 然后您的所有方法都可以訪問您的表單控件。

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 WindowsFormsApplication8
{
public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
    } 

        private MySqlConnection connection;
        private string server;
        private string database;
        private string uid;
        private string password;

        //Initialize values
        private void Initialize()
        {
            server = "net";
            database = "rainbow";
            uid = "ok";
            password = "passwd!";
            string connectionString;
            connectionString = "SERVER=" + server + ";" + "DATABASE=" +
            database + ";" + "UID=" + uid + ";" + "PASSWORD=" + password + ";";

            connection = new MySqlConnection(connectionString);
        }

        //open connection to database
        private bool OpenConnection()
        {

            try
            {
                connection.Open();
                return true;
            }
            catch (MySqlException ex)
            {
                //When handling errors, you can your application's response based 
                //on the error number.
                //The two most common error numbers when connecting are as follows:
                //0: Cannot connect to server.
                //1045: Invalid user name and/or password.
                switch (ex.Number)
                {
                    case 0:
                        MessageBox.Show("Cannot connect to server.  Contact administrator");
                        break;

                    case 1045:
                        MessageBox.Show("Invalid username/password, please try again");
                        break;
                    default :
                        MessageBox.Show("Connected Successfuly!!");
                        break;
                }
                return false;
            }


        }

        //Close connection
        private bool CloseConnection()
        {
            try
            {
                connection.Close();
                return true;
            }
            catch (MySqlException ex)
            {
                MessageBox.Show(ex.Message);
                return false;
            }
        }

        //Insert statement
        public void Insert()
        {
            string query = "INSERT INTO mytable (username, password) VALUES('shryder', 'nopassword')";

            //open connection
            if (this.OpenConnection() == true)
            {
                //create command and assign the query and connection from the constructor
                MySqlCommand cmd = new MySqlCommand(query, connection);

                //Execute command
                cmd.ExecuteNonQuery();

                //close connection
                this.CloseConnection();
            }
        }

        //Update statement
        public void Update()
        {
        }

        //Delete statement
        public void Delete()
        {

        }

        //Select statement
        public List<string>[] Select()
        {
            string query = "SELECT * FROM mytable";

            //Create a list to store the result
            List<string>[] list = new List<string>[3];
            list[0] = new List<string>();
            list[1] = new List<string>();
            list[2] = new List<string>();

            //Open connection
            if (this.OpenConnection() == true)
            {
                //Create Command
                MySqlCommand cmd = new MySqlCommand(query, connection);
                //Create a data reader and Execute the command
                MySqlDataReader dataReader = cmd.ExecuteReader();

                //Read the data and store them in the list
                if (dataReader.Read())
                {
                    /*list[0].Add(dataReader["username"] + "");
                    list[1].Add(dataReader["password"] + "");
                    list[2].Add(dataReader["email"] + "");*/
                    newscontent.Text = dataReader["username"]; //this is the error


                }

                //close Data Reader
                dataReader.Close();

                //close Connection
                this.CloseConnection();

                //return list to be displayed
                return list;
            }
            else
            {
                return list;
            }
        }

        //Count statement


        //Backup
        public void Backup()
        {
        }

        //Restore
        public void Restore()
        {
        }
    }



}
}

像這樣你的代碼應該能夠訪問標簽，所以它應該編譯。 它仍然沒有做任何事情，因為沒有調用任何方法。
在我的手機上編輯了這個，所以無法測試代碼。