Question

我对vb不太了解，并且从以前的程序员那里继承了一个应用程序。我被要求对代码运行Visual Studio分析以进行更改，因为该应用程序似乎引起了内存问题。我收到大量有关多次处置对象的消息，例如

警告CA2202在方法xxx'中可以多次放置对象'myConnection'。为避免生成System.ObjectDisposedException，您不应在对象上多次调用Dispose。

简单，将其包装在我认为的using块中。然后我发现myConnection用于try / catch

JumpUpAgain:
Try
    myConnection.Open()
Catch ex As Exception
                LogIt("EXCEPTION", "Connection Error: " & ex.Message)
                myConnection.Close()
                SqlConnection.ClearAllPools()
                ConnectionString = Nothing
                conn = Nothing
                MySQLCmd = Nothing
                myConnection = Nothing

                Threading.Thread.Sleep(3000)

                If ErrorLoopCounter = 5 Then
                    LogItDetail("Exception", "Database Connection Process failed after 5 re-tries")
                    If Not FailedFiles.Contains(InputFileName) Then FailedFiles.Add(InputFileName)
                    LogItDetail("DEBUG", "Added file to Failed Files for email")
                    FileProcessFailed = True
                    Throw
                Else
                    ErrorLoopCounter += 1
                End If
                GoTo JumpUpAgain

 End Try

在以后的代码中需要myConnection对象。我将从catch中删除myConnection = Nothing，但是如果我在try / catch块之外放置了use / end using，如果应用程序命中了Throw，它将正确处理吗？

Answer 1

使用代码块可确保即使发生错误，也可以关闭并处置db对象（与关闭同等重要）。您必须适应Try Catch，因为在块外定义的变量在块外不可见。

    Private Sub OPCode2()
        Dim dt As New DataTable()
        'Keep your connections local
        Using cn As New MySqlConnection("Your Connection String")
            Using cmd As New MySqlCommand("Select * From YourTable", cn)
                Try
                    cn.Open()
                    Using dr As MySqlDataReader = cmd.ExecuteReader
                        dt.Load(dr) 'or whatever you want to do with your connection
                    End Using
                Catch
                    'Your logging logic here
                End Try
            End Using
        End Using
    End Sub

使用和尝试/捕获块

1 个答案: