问批量FTPWebRequest

EN

permissionSet =  new Set(Types::Class);
files = new List(types::String);
permissionset.add(new InteropPermission(InteropKind::DllInterop));
permissionset.add(new InteropPermission(InteropKind::ClrInterop));
CodeAccessPermission::assertMultiple(permissionset);
ftpo = System.Net.WebRequest::Create(<ftp link>);
request = ftpo;
request.set_KeepAlive(false);
request.set_UsePassive(false);
request.set_UseBinary(true);
request.set_Method("NLST");
credential = new System.Net.NetworkCredential(<user>,<pw>);
request.set_Credentials(credential);
try
{
    //first get the filelist from FTP
    response = request.GetResponse();
    reader = new System.IO.StreamReader(response.GetResponseStream());
    while(!reader.get_EndOfStream())
    {
        text = reader.ReadLine();
        files.addStart(text);
    }
    reader.Close();
    response.Close();
    CodeAccessPermission::revertAssert();
    if(files.elements() >0)
    {
        it = New ListIterator(files);
        while(it.more())
        {
            filename = it.value();
            downloadfile(filename);
            deleteFile(filename);
            it.next();
        }
    }
}

System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.Net.WebException: The operation has timed out.
   at System.Net.FtpWebRequest.CheckError()
   at System.Net.FtpWebRequest.GetResponse()
   --- End of inner exception stack trace ---
   at System.RuntimeMethodHandle._InvokeMethodFast(Object target, Object[] arguments, SignatureStruct& sig, MethodAttributes methodAttributes, RuntimeTypeHandle typeOwner)
   at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture, Boolean skipVisibilityChecks)
   at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
   at ClrBridgeImpl.InvokeClrInstanceMethod(ClrBridgeImpl* , ObjectWrapper* objectWrapper, Char* pszMethodName, Int32 argsLength, ObjectWrapper** arguments, Boolean* argsAreByRef, Boolean* isException)