Question

请查看以下代码：

Public Class Form1
    Private _ConString As String
    Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        Dim objDR As SqlDataReader
        Dim objCommand As SqlCommand
        Dim objCon As SqlConnection
        Dim id As Integer
        Try
            _ConString = ConfigurationManager.ConnectionStrings("TestConnection").ToString
            objCon = New SqlConnection(_ConString)
            objCommand = New SqlCommand("SELECT * FROM Person")
            objCommand.Connection = objCon
            objCon.Open()
            objDR = objCommand.ExecuteReader(ConnectionState.Closed)
            Do While objDR.Read
                id = objDR("URN")
            Loop
            objDR.Close() 'line 16
        Catch ex As Exception
            throw
        Finally

        End Try

    End Sub
End Class

连接对象在第16行关闭。请查看下面的代码：

Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        Dim objDR As SqlDataReader
        Dim objCommand As SqlCommand
        Dim objCon As SqlConnection
        Dim id As Integer
        Try
            _ConString = ConfigurationManager.ConnectionStrings("TestConnection").ToString
            objCon = New SqlConnection(_ConString)
            objCommand = New SqlCommand("SELECT * FROM Person")
            objCommand.Connection = objCon
            objCon.Open()
            Using objCon
                Using objCommand
                    objDR = objCommand.ExecuteReader()
                    Do While objDR.Read
                        id = objDR("URN")
                    Loop
                End Using
            End Using
            objDR.Close() 'line 16
        Catch ex As Exception
           throw
        Finally

        End Try

    End Sub

在这两种情况下，我都注意到连接对象和命令对象在关闭后仍然具有状态（通过按照代码示例1关闭数据读取器或按照代码示例2移动到Using语句之外）。这可能是内存泄漏的来源吗？

Answer 1

你应该做这样的事情......

Using Conn as new SqlConnection(_ConString)
 Dim cmd as New SqlCommand(Conn, "Select * FROM Person");
   id = Convert.ToInt32(cmd.ExecuteScalar())
End Using

如果必须，请尝试将其包裹起来，但前提是您要以某种方式处理它。（一个简单的“投掷”不处理任何事情。）

您还使用DataReader（仅迭代，仅转发）数据访问组件来获取单个值。您可能希望使用ExecuteScalar（）来简化该代码。

除此之外，不要将“Disposed”混淆为与“Closed”相同。 .NET框架为您管理垃圾收集。如果你想处理连接和命令对象，请在它们上面调用.Dispose（）（但是Using会为你处理这个!!!）

Answer 2

re：这可能是内存泄漏的来源吗？ 不，它不应该是。

另外，这个：

            objDR = objCommand.ExecuteReader()
            Do While objDR.Read
                id = objDR("URN")
            Loop

看起来很糟糕，因为它遍历所有行并覆盖id值。最后一行设置以ID中的值结束。您从一组多行中获取一个结果。如果您只想要来自max(URN)的{{1}}，您可以编写命令以返回该结果。

VB.NET - 关闭Connection对象和命令对象

2 个答案: