Dim f As New FileIOPermission(PermissionState.None)
f.AllLocalFiles = FileIOPermissionAccess.Read
Try
    f.Demand()
Catch s As SecurityException
    Console.WriteLine(s.Message)
End Try

Dim f2 As New FileIOPermission(FileIOPermissionAccess.Read, "C:\test_r")
f2.AddPathList(FileIOPermissionAccess.Write Or FileIOPermissionAccess.Read, "C:\example\out.txt")
Try
    f2.Demand()
Catch s As SecurityException
    Console.WriteLine(s.Message)
End Try

' 导入命名空间
Imports System.Security.Principal
Imports System.Security.Permissions
Imports System.IO


public class MainClass
   Shared Sub Main()
        Dim oFp As FileIOPermission = New FileIOPermission(FileIOPermissionAccess.Write, "d:\test.txt")
        oFp.Assert()
        Try
            Dim objWriter As New IO.StreamWriter(File.Open("d:\test.txt", IO.FileMode.Open))
            objWriter.WriteLine("Hi there!")
            objWriter.Flush()
            objWriter.Close()
            objWriter = Nothing
        Catch objA As System.Exception
            Console.WriteLine(objA.Message)
        End Try

   End Sub
End Class