如何處理使用VB.net未處理的NullReference異常

Question

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load 

    Try 

     connn_start() 

     Dim Query As String 
     Query = "Select * from abc.abc_list" 

     Dim dbcomm = New MySqlCommand(Query, dbconn) 
     While dbread.Read 'error is throwing at this point 
      Dim DB_VName = dbread.GetString("abc_name") 
      cb_V_Name.Items.Add(DB_Name) 
     End While 

     Connn_stop() 

    Catch ex As MySqlException 
     MessageBox.Show(ex.Message) 

    Finally 
     dbconn.Dispose() 
    End Try 

如何處理此異常？

Answer 1

讀前添加：什麼是一個NullReferenceException，如何解決呢]的

SqlDataReader dbread=dbcomm.ExecuteReader(); 
if (reader.HasRows) 
{ 
    while (reader.Read()) 
    { 
    ... 
    } 
}