vb.net用SqlDataAdapter逐行读取，急急急
这是我的代码： '读取数据
Dim cmd As System.Data.SqlClient.SqlCommand = New System.Data.SqlClient.SqlCommand()
Dim dr As System.Data.SqlClient.SqlDataReader = cmd.ExecuteReader()
Dim sw As System.IO.StreamWriter = New System.IO.StreamWriter("dtcontacts")

While (dr.Read())
For rr As Integer = 0 To dr.FieldCount - 1 Step 1
Try
Dim ss As String = dr.GetString(rr)
Catch ex As Exception

End Try
Next
End While
dr.Close()

End Sub
提示红色部分ExecuteReader: Connection 属性尚未初始化。不知道是怎么个改法，麻烦各位帮我看看。