我是否需要处理自定义 class 的实例以释放内存？那怎么办？ VB.NET

Question

我只是想在执行我的 SQL 查询时节省时间和代码来创建自定义 class，所以我这样创建：

Imports ADODB

Public Class MySQLConnection
    Private SQLConnection As ADODB.Connection
    Private SQLConnectionString As String = "Provider=SQLOLEDB;Data Source=111.111.10.201;Initial Catalog=dbSample;User ID=User;password=123456;"
    Private SQLRecordSet As ADODB.Recordset
    Public Recordset As ADODB.Recordset
    Public Message As String

    Public Function ExecuteSQLQuery(vQuery As String) As Boolean
        Try
            SQLConnection.Open(SQLConnectionString)

            SQLRecordSet.CursorLocation = ADODB.CursorLocationEnum.adUseClient
            SQLRecordSet.CursorType = ADODB.CursorTypeEnum.adOpenStatic
            SQLRecordSet.LockType = ADODB.LockTypeEnum.adLockBatchOptimistic

            SQLRecordSet.Open(vQuery, SQLConnection)

            Recordset = SQLRecordSet 'passing the content of recordset to a public recordset for later use in my main program.

            SQLRecordSet.Close()

            SQLConnection.Close()

            Message = "Query executed successfully."
            Return True

        Catch ex As Exception
            Message = ex.Message
            Return False

        End Try
    End Function
End Class

问题#1 但是由于我将在整个程序中创建此 class 的多个实例，我是否需要以某种方式处理实例以在使用后立即释放内存？

每当我需要执行查询时，我都会在我的主程序中使用下面的代码：

    Private Sub COnnectToolStripMenuItem_Click(sender As Object, e As EventArgs) Handles COnnectToolStripMenuItem.Click
        Dim DB_CONN As New MySQLConnection
        If DB_CONN.ExecuteSQLQuery("SELECT * FROM tbl_Stores") Then

            If DB_CONN.Recordset.RecordCount <> 0 Then
                DB_CONN.Recordset.MoveFirst()
                Do While Not DB_CONN.Recordset.EOF
                    'Read each record here
                    DB_CONN.Recordset.MoveNext()
                Loop
            End If

            DB_CONN.Recordset.Close()

            '==============================
            'This is where I think I should dispose my class instance [DB_CON].

            MsgBox("MESSAGE: " & DB_CONN.Message)
        Else
            MsgBox("ERROR: " & DB_CONN.Message)
        End If
    End Sub

问题 #2： 我如何在使用后处理 class 的实例？

我只想知道这个，这样我就可以清理我以前的程序了。

我在 Google 中找到的所有内容都是针对 C++ 的，所以我不确定它是否适用于 VB.Net

请帮忙！ :(

Answer 1

如果我是你，我会考虑让 ExecuteSQLQuery 完全独立，这样它就需要一个 Action(Of ADODB.Recordset)。然后它可以在执行后立即自行清理。

我最初会这样写：

Public Module MySQLConnection
    Private SQLConnectionString As String = "Provider=SQLOLEDB;Data Source=111.111.10.201;Initial Catalog=dbSample;User ID=User;password=123456;"
    Public Function ExecuteSQLQuery(vQuery As String, process As Action(Of ADODB.Recordset), message As Action(Of String)) As Boolean
        Try
            Dim conn As ADODB.Connection = New ADODB.Connection()
            conn.Open(SQLConnectionString)
            Dim rs As ADODB.Recordset = New ADODB.Recordset()
            rs.CursorLocation = ADODB.CursorLocationEnum.adUseClient
            rs.CursorType = ADODB.CursorTypeEnum.adOpenStatic
            rs.LockType = ADODB.LockTypeEnum.adLockBatchOptimistic
            rs.Open(vQuery, conn)
            process?(rs)
            rs.Close()
            conn.Close()
            message?("Query executed successfully.")
            Return True
        Catch ex As Exception
            message?(ex.Message)
            Return False
        End Try
    End Function
End Module

现在你可以这样使用它：

Private Sub COnnectToolStripMenuItem_Click2(sender As Object, e As EventArgs) Handles COnnectToolStripMenuItem.Click
    Dim success As Boolean = MySQLConnection.ExecuteSQLQuery("SELECT * FROM tbl_Stores",
        Sub(recordset)
            If recordset.RecordCount <> 0 Then
                recordset.MoveFirst()
                Do While recordset.EOF
                    'Read each record here
                    recordset.MoveNext()
                Loop
            End If
        End Sub, AddressOf MsgBox)
End Sub

甚至更好——使方法 return 成为某个值的可枚举对象：

Public Module MySQLConnection
    Private SQLConnectionString As String = "Provider=SQLOLEDB;Data Source=111.111.10.201;Initial Catalog=dbSample;User ID=User;password=123456;"
    Public Iterator Function ExecuteSQLQuery2(Of T)(vQuery As String, process As Func(Of ADODB.Recordset, T)) As IEnumerable(Of T)
        Dim conn As ADODB.Connection = New ADODB.Connection()
        conn.Open(SQLConnectionString)
        Dim rs As ADODB.Recordset = New ADODB.Recordset()
        rs.CursorLocation = ADODB.CursorLocationEnum.adUseClient
        rs.CursorType = ADODB.CursorTypeEnum.adOpenStatic
        rs.LockType = ADODB.LockTypeEnum.adLockBatchOptimistic
        rs.Open(vQuery, conn)
        If rs.RecordCount <> 0 Then
            rs.MoveFirst()
            Do While rs.EOF
                Yield process(rs)
                rs.MoveNext()
            Loop
        End If
        rs.Close()
        conn.Close()
    End Function
End Module

那么你可以这样做：

Private Sub COnnectToolStripMenuItem_Click2(sender As Object, e As EventArgs) Handles COnnectToolStripMenuItem.Click
    Dim values As IEnumerable(Of Integer) = MySQLConnection.ExecuteSQLQuery2(Of Integer)("SELECT * FROM tbl_Stores", Function(recordset) CType(recordset.Fields("Value").Value, Integer))
End Sub

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