Mysqlbackup错误2.0.4

Question

我尝试用代码来备份我的数据库使用以下2.0.4 mysqlBackUp

private void button9_Click_1(object sender, EventArgs e) 
     { 
      try 
      { 
       string constring = "Data Source=localhost;User Id=root;Password=sulyman;database=accounting_db"; 
       MySqlConnection conn = new MySqlConnection(constring); 
       string file = "D:\\backup.sql"; 
       cmd = new MySqlCommand(); 
       cmd.Connection = conn; 
       dal.Open(); 
       MySqlBackup ba = new MySqlBackup(cmd); 
       ba.ExportToFile(file); 
       dal.close(); 
       MessageBox.Show("done"); 
      } 
      catch(Exception ex) 
      { MessageBox.Show(ex.Message); } 


     } 

，但我在该行得到了错误

a object reference note set to an instance of an object 

ba.ExportToFile(file); 

哪里是错我的代码，请

Answer 1

问题：似乎数据库连接未打开，或者您正在使用dal.Open()而不是conn.Open()。

1. 我评论dal.Open();，dal.Close();并加入conn.Open();
2. Delcared MySqlCommand内部方法。
3. 新增using声明

试试这个代码：

private void button9_Click_1(object sender, EventArgs e) 
    { 
     try 
     { 
      string constring = "Data Source=localhost;User Id=root;Password=sulyman;database=accounting_db"; 
      string file = "D:\\backup.sql"; 
      using(MySqlConnection conn = new MySqlConnection(constring))     
      using(MySqlCommand cmd = new MySqlCommand()) 
      { 
       cmd.Connection = conn; 
       conn.Open(); //dal.Open(); 
       using(MySqlBackup ba = new MySqlBackup(cmd)) 
       { 
        ba.ExportToFile(file); 
        //dal.close(); 
        MessageBox.Show("done"); 
       } 
      } 

     catch(Exception ex) 
     { MessageBox.Show(ex.Message); } 

    }