vb.net - 在处理 VB .NET 4.5 中的文件之前测试我是否具有对文件的完全读/写访问权限

Question

我正在编写一个以本地系统帐户运行的 Windows 服务。我试图确保我是否具有对文件的完全读/写访问权限，开始进一步处理它。这是我的代码:

    Dim FullPath As String
    FullPath = "C:\directory\file.txt"
    Dim ps As Security.PermissionSet
    ps = New Security.PermissionSet(Security.Permissions.PermissionState.Unrestricted)
    ps.AddPermission(New Security.Permissions.FileIOPermission(Security.Permissions.FileIOPermissionAccess.AllAccess, FullPath))
    ps.AddPermission(New Security.Permissions.FileIOPermission(Security.Permissions.FileIOPermissionAccess.AllAccess, IO.Path.GetDirectoryName(FullPath)))
    Try
        ps.Demand()
    Catch ex As Security.SecurityException
        System.Diagnostics.EventLog.WriteEntry("ShopLink", "File " + FullPath + " will not be parsed. " + ex.Message)
        Exit Sub
    Catch ex As Exception
        System.Diagnostics.EventLog.WriteEntry("ShopLink", "File " + FullPath + " will not be parsed. " + ex.Message)
        Exit Sub
    End Try

然后，我将运行服务的用户帐户的文件完全访问权限设置为“拒绝”。执行后，上面的代码不会抛出任何异常并允许开始文件处理。当服务稍后尝试更改和/或删除文件时，我收到“访问被拒绝”异常。

有什么建议吗？

Answer 1

为此，我使用这个小函数:

  Private Function HasAccess(ByVal ltFullPath As String)
    Try
      Using inputstreamreader As New StreamReader(ltFullPath)
        inputstreamreader.Close()
      End Using
      Using inputStream As FileStream = File.Open(ltFullPath, FileMode.Open, FileAccess.ReadWrite, FileShare.None)
        inputStream.Close()
        Return True
      End Using
    Catch ex As Exception
      Return False
    End Try
  End Function

在你的情况下:

If HasAccess(FullPath) ...