override Sub finalize以确保与数据库的连接已关闭

Question

我正在连接Access数据库，我想知道在我的cconnectionDB.vb中重写Sub finalize是否有用：

Imports System.Data.SqlClient
Imports System.Data.Common
Imports System.IO
Public Class DbConn
    Private DataCon As DbConnection
    Private DBConnectionOpen As Boolean = False
     Protected Overrides Sub finalize()
            Try
                DataCon.Close()
            Catch ex As Exception
            End Try
        End Sub
    Public Sub OpenDatabaseConnection()
        Try
            DataCon.Open()
        Catch ex As Exception
            Throw New System.Exception("Error opening data connection.", ex.InnerException)
            DBConnectionOpen = False
            Exit Sub
        End Try
        DBConnectionOpen = True
    End Sub 
    Public Sub CloseDatabaseConnection()
        DataCon.Close()
        DBConnectionOpen = False
    End Sub

   ''' <summary>
    ''' Creates a new connection to an Access database
    ''' </summary>
    ''' <param name="FileName">The full path of the Access file</param>
    ''' <remarks></remarks>
    Public Sub New(ByVal FileName As String)
        'Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:myFoldermyAccess2007file.accdb;Persist Security Info=False;
        Dim fileData As FileInfo = My.Computer.FileSystem.GetFileInfo(FileName)
        DataCon = New OleDb.OleDbConnection
        Dim csb As OleDb.OleDbConnectionStringBuilder = New OleDb.OleDbConnectionStringBuilder
        csb.ConnectionString = "Data Source=" & FileName
        Select Case fileData.Extension.ToLower
            Case ".mdb" : csb.Add("Provider", "Microsoft.Jet.Oledb.4.0")
            Case ".accdb" : csb.Add("Provider", "Microsoft.ACE.OLEDB.12.0")
        End Select
        DataCon.ConnectionString = csb.ConnectionString
        Try
            DataCon.Open()
            DataCon.Close()
        Catch ex As Exception
            Throw New System.Exception("Unable to connect to database.", ex.InnerException)
        End Try
    End Sub
End Class

Answer 1

这并不是很有用。直到垃圾收集器开始销毁对象，才会调用Finalize解构器。而且，由于DbConn对象将是唯一引用DbConnection对象的对象，因此无论如何，它都会同时自动销毁该对象。如果您想在完成连接后立即释放连接，建议的方法是在类中实现IDisposable接口。例如：

Private Class DbConn
    Implements IDisposable
    Private DataCon As DbConnection
    Private disposedValue As Boolean
    Protected Overridable Sub Dispose(disposing As Boolean)
        If Not Me.disposedValue Then
            If disposing Then
                Try
                    DataCon.Close()
                Catch ex As Exception
                End Try
            End If
        End If
        disposedValue = True
    End Sub
    Public Sub Dispose() Implements IDisposable.Dispose
        Dispose(True)
        GC.SuppressFinalize(Me)
    End Sub
End Class

然而，如果您实现了IDisposable，那么您的工作还没有完成。IDisposable对象上的Dispose方法从未被自动调用。您需要通过手动调用Dispose方法来告知对象何时完成处理。或者，您可以使用Using块：

Using d As New DbConn
    ' The DbConn.Dispose method automatically gets called once execution leaves this Using block
End Using