在列表中創建一個列表，並將數據存入MYSQL

Question

我想在列表中創建一個列表，將數據放入MYSQL中... 我很接近，但它似乎不能正常工作...

當我MessageBox.Show(list_line[0][3].ToString()); 它給了我System.IndexOutOfRangeException但在技術上，我想要什麼，並認爲這樣做是：

list_DB[ [list_line1] , [List_line2] , [list_line3] , ... ] 

和list_line看起來像[1, 22/02/2017 13:48:01, 50.0000, 004.0000]

這是我本功能離子...

private List<string> list_line = new List<string>(); 
    private List<List<string>> list_DB = new List<List<string>>(); 
    private void BoatGPS_INTO_LIST() 
    { 
     SqlDataReader reader; 
     string query = "select boat_id, boatGPS_DateTime, boatGPS_lat, boatGPS_lon from BoatGPS"; 

     using (SqlConnection sql = new SqlConnection("Data Source = (LocalDB)\\MSSQLLocalDB; AttachDbFilename = \"" + Environment.CurrentDirectory + "\\DB\\STS.mdf\"; Integrated Security = True; Connect Timeout = 30")) 
     { 
      sql.Open(); 
      using (reader = new SqlCommand(query, sql).ExecuteReader()) 
      { 
       if (reader.HasRows) 
       { 
        while (reader.Read()) 
        { 
         Object[] line = new Object[reader.FieldCount]; 
         reader.GetValues(line);        
         foreach (var item in line) 
         { 
          list_line.Add(item.ToString()); 
         } 
         list_DB.Add(list_line); 
        } 
       } 
      } 
      MessageBox.Show(list_line[0][3].ToString()); 
      sql.Close(); 
     } 
    } 

Answer 1

list_DB的類型是List<List<string>>。嘗試：

MessageBox.Show(list_DB[0][3].ToString()); 

編輯： 關於如何填寫清單list_DB，請嘗試：

while (reader.Read()) 
{ 
    List<string> list_line = new List<string>();       
    list_line.Add(reader[0].ToString()); 
    list_line.Add(reader[1].ToString()); 
    list_line.Add(reader[2].ToString()); 
    list_line.Add(reader[3].ToString()); 

    list_DB.Add(list_line); 
} 

Answer 2

此代碼

MessageBox.Show(list_line[0][3].ToString()); 

試圖訪問的拳頭項目（串）在list_line對象（List<string>）中，然後character與該字符串中的索引3，這將拋出excep如果字符串短於4個字符

Answer 3

你很複雜的東西。不需要這樣的結構。
有一個特定的類在內存中表示SELECT查詢的結果，它是DataTable類。

private DataTable dt = new DataTable(); 
private void BoatGPS_INTO_LIST() 
{ 
    SqlDataReader reader; 
    string query = "select boat_id, boatGPS_DateTime, boatGPS_lat, boatGPS_lon from BoatGPS"; 

    using (SqlConnection sql = new SqlConnection("Data Source = (LocalDB)\\MSSQLLocalDB; AttachDbFilename = \"" + Environment.CurrentDirectory + "\\DB\\STS.mdf\"; Integrated Security = True; Connect Timeout = 30")) 
    { 
     sql.Open(); 
     using (reader = new SqlCommand(query, sql).ExecuteReader()) 
      dt.Load(reader); 

     if(dt.Rows.Count > 0) 
      // Here the syntax means: First row, fourth column 
      MessageBox.Show(dt.Rows[0][3].ToString()); 
     else 
      MessageBox.Show("Table is empty"); 


    } 
}