HTTP POST参数编码错误ANDROID

I am developing an Android App. I need to connect to my PHP and i am usig HttpPost. This is my code. I've followed several tutorials and it doesn't work. The error is that the PHP doesn't receive the parameters that I pass from my App code. Although it connects correctly to the PHP. I've used POSTman to find errors in the PHP but it works fine. I put my code here :

private void httppostconnect(ArrayList<NameValuePair> parametros, String urlwebserver) {
    try {
        HttpClient httpclient = new DefaultHttpClient();
        HttpPost httppost = new HttpPost(urlwebserver);
        httppost.setEntity(new UrlEncodedFormEntity(parametros));
        //ejecuto peticion enviando datos por POST
        HttpResponse response = httpclient.execute(httppost);
        HttpEntity entity = response.getEntity();
        is = entity.getContent();
    } catch(Exception e) {
        Log.e("GetBuscadas", "Error in http connection "+e.toString());
    }
}

Can you clarify what those parameters are, your "parametros" var. The usual problem would be not sending content type headers.