如何解决从网站下载后关闭 MSI 文件句柄
我有一个用于 Outlook 的 vsto 加载项。有一个代码可以让我从网站下载 MSI 文件:
Public Sub DownloadMsiFile()
Try
Dim url As String = "https://www.website.com/ol.msi"
Dim wc As New WebClient()
wc.Headers.Add(HttpRequestHeader.UserAgent,"Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.2; .NET CLR 1.0.3705;")
If File.Exists(My.Computer.FileSystem.SpecialDirectories.Temp & "\ol.msi") Then
System.IO.File.Delete(My.Computer.FileSystem.SpecialDirectories.Temp & "\ol.msi")
End If
wc.DownloadFile(url,My.Computer.FileSystem.SpecialDirectories.Temp & "\ol.msi")
wc.Dispose()
Catch ex As Exception
MessageBox.Show("File couldn't be downloaded: " & ex.Message)
End Try
End Sub
然后我使用以下函数获取 MSI 版本:
Function GetMsiVersion() As String
Try
Dim oInstaller As WindowsInstaller.Installer
Dim oDb As WindowsInstaller.Database
Dim oView As WindowsInstaller.View
Dim oRecord As WindowsInstaller.Record
Dim sSQL As String
oInstaller = CType(CreateObject("WindowsInstaller.Installer"),WindowsInstaller.Installer)
DownloadMsiFile()
If File.Exists(My.Computer.FileSystem.SpecialDirectories.Temp & "\ol.msi") Then
oDb = oInstaller.OpenDatabase(My.Computer.FileSystem.SpecialDirectories.Temp & "\ol.msi",0)
sSQL = "SELECT `Value` FROM `Property` WHERE `Property`='ProductVersion'"
oView = oDb.OpenView(sSQL)
oView.Execute()
oRecord = oView.Fetch
Return oRecord.StringData(1).ToString()
Else
Return Nothing
End If
Catch ex As Exception
MessageBox.Show("File couldn't be accessed: " & ex.Message)
End Try
End Function
然后我和当前的dll版本进行对比,看看是否需要下载更新的版本:
Public Sub CheckOLUpdates()
Dim remoteVersion As String = GetMsiVersion()
Dim installedVersion As String = Assembly.GetExecutingAssembly().GetName().Version.ToString
If Not String.IsNullOrEmpty(remoteVersion) Then
Try
If String.Compare(installedVersion,remoteVersion) < 0 Then
Dim Result As DialogResult = MessageBox.Show("A newer version is available for download,do you want to download it now?","OL",System.Windows.Forms.MessageBoxButtons.OKCancel,MessageBoxIcon.Question)
If Result = 1 Then
System.Diagnostics.Process.Start("http://www.website.com/update")
Else
Exit Sub
End If
Else
MessageBox.Show("You have the latest version installed!",MessageBoxButtons.OK,MessageBoxIcon.Information)
End If
Catch ex As Exception
End Try
End If
End Sub
如果运行一次,这会很有效。但是,如果我再次尝试检查更新,我会在尝试删除 DownloadMsiFile() 中的文件时收到以下错误:
进程无法访问文件 %temp%\ol.msi,因为它正被另一个进程使用
如果我使用 sysinternals handle.exe 实用程序来检查此文件的句柄,我会发现 Outlook 进程对该文件具有句柄锁定:
handle.exe %temp%\ol.msi
Nthandle v4.30 - Handle viewer
Copyright (C) 1997-2021 Mark Russinovich
Sysinternals - www.sysinternals.com
OUTLOOK.EXE pid: 25964 type: File 4FC8: %temp%\ol.msi
我想知道如何关闭句柄以避免此错误?非常感谢任何帮助
解决方法
所以这是我必须做的才能关闭手柄。我在打开 MSI 文件后添加了以下几行:
Marshal.FinalReleaseComObject(oRecord)
oView.Close()
Marshal.FinalReleaseComObject(oView)
Marshal.FinalReleaseComObject(oDb)
oRecord = Nothing
oView = Nothing
oDb = Nothing
所以我的最终代码如下所示:
Function GetMsiVersion() As String
Try
Dim oInstaller As WindowsInstaller.Installer
Dim oDb As WindowsInstaller.Database
Dim oView As WindowsInstaller.View
Dim oRecord As WindowsInstaller.Record
Dim sSQL As String
Dim Version As String
oInstaller = CType(CreateObject("WindowsInstaller.Installer"),WindowsInstaller.Installer)
DownloadMsiFile()
If File.Exists(My.Computer.FileSystem.SpecialDirectories.Temp & "\ol.msi") Then
oDb = oInstaller.OpenDatabase(My.Computer.FileSystem.SpecialDirectories.Temp & "\ol.msi",0)
sSQL = "SELECT `Value` FROM `Property` WHERE `Property`='ProductVersion'"
oView = oDb.OpenView(sSQL)
oView.Execute()
oRecord = oView.Fetch
Version = oRecord.StringData(1).ToString()
Marshal.FinalReleaseComObject(oRecord)
oView.Close()
Marshal.FinalReleaseComObject(oView)
Marshal.FinalReleaseComObject(oDb)
oRecord = Nothing
oView = Nothing
oDb = Nothing
Else
Version = Nothing
End If
Return Version
Catch ex As Exception
MessageBox.Show("File couldn't be accessed: " & ex.Message)
End Try
End Function
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