ExecuteReader 要求已打开且可用的 Connection。连接的当前状态为已关闭。请问大佬知道这个是什么原因吗？

Question

ExecuteReader 要求已打开且可用的 Connection。连接的当前状态为已关闭。请问大佬知道这个是什么原因吗？
源代码如下：
string name = textBox1.Text.Trim();
string password1 = textBox2.Text.Trim();
string password2 = textBox3.Text.Trim();
string Name = textBox4.Text.Trim();
string number = textBox5.Text.Trim();
if (name == “”)
{
MessageBox.Show(“用户名不能为空！”, “登录失败”, MessageBoxButtons.OK, MessageBoxIcon.Information);
}
else
{
if (password1 != password2)
{
MessageBox.Show(“两次输入的密码不一致！”, “登录失败”, MessageBoxButtons.OK, MessageBoxIcon.Information);
}
else
{
SqlConnection con = new SqlConnection();
con.ConnectionString = “Data source=(local);Initial Catalog=Management;Integrated Security=True”;                SqlCommand cmd = new SqlCommand();
                cmd.CommandText = "select username from manager";
                cmd.Connection = con;
                SqlDataReader reader = cmd.ExecuteReader();
                while(reader.Read())
                {
                    string username = reader["username"].ToString();
                    if (name == username)
                    {
                        MessageBox.Show("用户名已存在！", "注册失败", MessageBoxButtons.OK, MessageBoxIcon.Information);
                        
                    }
                      
                    else
                    {
                        string sql = "insert into manager(username,pwd,name,ID)values(" + name + "," + password1 + "," + Name + "," + number + ")";
                        try
                        {
                            
                            SqlCommand comm = new SqlCommand(sql, con);
                            int count = comm.ExecuteNonQuery();
                            if (count >= 0)
                            {
                                MessageBox.Show("注册成功，请前往登录", "注册成功", MessageBoxButtons.OK, MessageBoxIcon.Information);
                            }
                            else
                                MessageBox.Show("注册失败", "注册失败", MessageBoxButtons.OK, MessageBoxIcon.Information);
                        }
                        catch (Exception ex)
                        {
                            MessageBox.Show(ex.Message, "数据库出错！", MessageBoxButtons.OK, MessageBoxIcon.Information);
                        }
                        finally
                        {
                            con.Close();
                        }
                        Form1 a = new Form1();
                        a.Show();
                        this.Visible=false;                    }
                        
                }            }
        }
--------------------- 
作者：Numb6 
来源：CSDN 
原文：https://blog.csdn.net/weixin_45013749/article/details/90085080 
版权声明：本文为博主原创文章，转载请附上博文链接！

Answer 1

你网上下个DBHelper类，不要把数据库处理还写在你的逻辑代码实现里面

Answer 2

 SqlDataReader reader = cmd.ExecuteReader();
在这行代码之前，加上con.open,只有打卡连接之后，才能read

Answer 3

加入了con.open()提示连接已打开，请先关闭原有连接

Answer 4

加入con.open（），运行还是报错，提示连接已打开，请先关闭原有的连接。

Answer 5

加入了con.open（），运行提示已有连接，请先关闭原有连接

Answer 6

在这个SqlDataReader reader = cmd.ExecuteReader();之前加上
if(con.connectingstate==connetingstate.close)
{
      con.open();
}

Answer 7

SQLDataReader类型的对象是需要保持连接打开，并且是按顺序读取的，所以你需要加入标识为红色的那行代码才行。
string name = textBox1.Text.Trim();
 string password1 = textBox2.Text.Trim();
 string password2 = textBox3.Text.Trim();
 string Name = textBox4.Text.Trim();
 string number = textBox5.Text.Trim();
 if (name == “”)
 {
MessageBox.Show(“用户名不能为空！”, “登录失败”, MessageBoxButtons.OK, MessageBoxIcon.Information);
 }
 else
 {
 if (password1 != password2)
 {
 MessageBox.Show(“两次输入的密码不一致！”, “登录失败”, MessageBoxButtons.OK, MessageBoxIcon.Information);
 }
 else
 {
 SqlConnection con = new SqlConnection();
con.ConnectionString = “Data source=(local);Initial Catalog=Management;Integrated Security=True”;                 SqlCommand cmd = new SqlCommand();
                 cmd.CommandText = "select username from manager";
                 cmd.Connection = con;
                 con.open(); 
                SqlDataReader reader = cmd.ExecuteReader();
                 while(reader.Read())
                 {
                     string username = reader["username"].ToString();
                     if (name == username)
                     {
                         MessageBox.Show("用户名已存在！", "注册失败", MessageBoxButtons.OK, MessageBoxIcon.Information);
                         
                     }
                       
                     else
                     {
                         string sql = "insert into manager(username,pwd,name,ID)values(" + name + "," + password1 + "," + Name + "," + number + ")";
                         try
                         {
                             
                             SqlCommand comm = new SqlCommand(sql, con);
                             int count = comm.ExecuteNonQuery();
                             if (count >= 0)
                             {
                                 MessageBox.Show("注册成功，请前往登录", "注册成功", MessageBoxButtons.OK, MessageBoxIcon.Information);
                             }
                             else
                                 MessageBox.Show("注册失败", "注册失败", MessageBoxButtons.OK, MessageBoxIcon.Information);
                         }
                         catch (Exception ex)
                         {
                             MessageBox.Show(ex.Message, "数据库出错！", MessageBoxButtons.OK, MessageBoxIcon.Information);
                         }
                         finally
                         {
                             con.Close();
                         }
                         Form1 a = new Form1();
                         a.Show();
                         this.Visible=false;                     }
                         
                 }             }
         }

Answer 8

public static MySqlDataReader ExecuteSql(string connectionString, string SQLString, int Times)
        {
            using (MySqlConnection connection = new MySqlConnection(connectionString))
            {
                using (MySqlCommand cmd = new MySqlCommand(SQLString, connection))
                {
                    try
                    {
                        connection.Open();
                        cmd.CommandTimeout = Times;
                        MySqlDataReader rows = cmd.ExecuteReader();
                        return rows;
                    }
                    catch (MySql.Data.MySqlClient.MySqlException e)
                    {
                        connection.Close();
                        throw e;
                    }
                }
            }
        }把取数据和逻辑分开

Answer 9

con.state <> connection.open 
con.open

Answer 10

首先在实例化Connection后，加上conn.Open()；然后你在while循环里边不要Close, 就是finally
                        {
                            con.Close();
                        }删掉；然后在循环外边再Close;