cancel httpTransport.call using ksoap in android

Question

I using ksoap lib for connecting to my Webservice.
my scenario is

1. showing a progress dialog
2. call my Webservice
   3-1. if done dismiss the dialog
   3-2. if the user cancels dialog then cancels calling operation

but I don't know how can I cancel call method after run it.
this is my call method

SoapObject request=null;
    request = new SoapObject(NameSpace,Operation);
request.addProperty(propertys.get(i));
SoapSerializationEnvelope envelope = new SoapSerializationEnvelope(SoapEnvelope.VER11);
    envelope.dotNet = true;
    envelope.setOutputSoapObject(request);

    Log.d(tag, "request="+request);

    HttpTransportSE httpTransport = new HttpTransportSE(db.getWebsiteAddress()+ db.getWebserviceName());
    Object response = null;

    try {
        httpTransport.call(db.getNameSpace()+Operation, envelope);    
        response = envelope.getResponse();
    } catch (Exception exception) {
        response = exception.toString();
        exception.printStackTrace();
    }      

so my question is, is there anyway to cancel httpTransport.call method?
thanks for any help.