Question

I am running a function inside Async task to get feed from a url on my server, it works but when there is no Internet connection it stops my application by giving a error message.

I am not sure how to handle this, anyways here goes my code

FUNCTION TO FETCH FEED

   public void getContent(){
    // Initializing instance variables
    headlines = new ArrayList<String>();
    links = new ArrayList<String>();
    server_images = new ArrayList<String>();

    try {
        URL url = new URL("http://www.uglobal.org/androidServer/courses_list.xml");

        XmlPullParserFactory factory = XmlPullParserFactory.newInstance();
        factory.setNamespaceAware(false);
        XmlPullParser xpp = factory.newPullParser();

            // We will get the XML from an input stream
        xpp.setInput(getInputStream(url), "UTF_8");

            /* We will parse the XML content looking for the "<title>" tag which appears inside the "<item>" tag.
             * However, we should take in consideration that the rss feed name also is enclosed in a "<title>" tag.
             * As we know, every feed begins with these lines: "<channel><title>Feed_Name</title>...."
             * so we should skip the "<title>" tag which is a child of "<channel>" tag,
             * and take in consideration only "<title>" tag which is a child of "<item>"
             *
             * In order to achieve this, we will make use of a boolean variable.
             */
        boolean insideItem = false;

            // Returns the type of current event: START_TAG, END_TAG, etc..
        int eventType = xpp.getEventType();
        while (eventType != XmlPullParser.END_DOCUMENT) {
            if (eventType == XmlPullParser.START_TAG) {

                if (xpp.getName().equalsIgnoreCase("item")) {
                    insideItem = true;
                } else if (xpp.getName().equalsIgnoreCase("title")) {
                    if (insideItem)
                        headlines.add(xpp.nextText()); //extract the headline
                } else if (xpp.getName().equalsIgnoreCase("link")) {
                    if (insideItem)
                        links.add(xpp.nextText()); //extract the link of article
                } else if (xpp.getName().equalsIgnoreCase("image")) {
                    if (insideItem)
                        server_images.add(xpp.nextText()); //extract the link of article
                }
            }else if(eventType==XmlPullParser.END_TAG && xpp.getName().equalsIgnoreCase("item")){
                insideItem=false;
            }

            eventType = xpp.next(); //move to next element
        }

    } catch (MalformedURLException e) {
        e.printStackTrace();
    } catch (XmlPullParserException e) {
        e.printStackTrace();
    } catch (UnknownHostException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

public InputStream getInputStream(URL url) {
   try {
       return url.openConnection().getInputStream();
   } catch (IOException e) {
       return null;
     }
}

Than i run this function inside the async task

ASYNC TASK

    private class PostTask extends AsyncTask<String, Integer, String>{
    @Override

    protected void onPreExecute() {
        // TODO Auto-generated method stub
        progressDialog = ProgressDialog.show(ListViewImagesActivity.this, "Loading","Getting Feed ", true);
    }
    protected String doInBackground(String... arg0) {
        getContent();
        return null;
    }
    }

Now if i have Internet connection it works fine but the moment i loose connection it kills my application with an error “Application Not Responding”

WHY I DON”T WANT TO RELY ON Connectivity Manager

Connectivity Manager just looks for the Internet connection , what if i am running behind a proxy and i need to be logged to my proxy server in order to access Internet ?

Is there any way to at least prevent my application from getting killed.

Answer 1

Quick answer

Sure, handle the exceptions on try/catch blocks: Even if the IDE wont tell you a function throws an exception they can be raised, in fact that seems to be your case right now.

Try running your application while completely offline and wrap each and every line that raises an exception in a try/catch block (Off course, a single try/catch for the whole “offending” code is enough as long as you catch all exceptions).

---

Tips and tricks

As for not wanting to rely on ConnectivityManager? That’s a bad idea. ConnectivityManager may not handle edge cases as college proxies and whatnot, but its still a protection layer. You dont want to waste precious computation time starting connections that you can know in advance will invariably fail, specially on a mobile phone.

Pro tip: You might want to check the presence of proxies in your own code before feeding the downloaded strings to the XML parsers, just check the first line. If that web service outputs proper XML it will most likely contain something around the likes of

<?xml version="1.0" encoding="UTF-8" ?>

so if the first line is not starting with something similar you can be sure its not XML.

Conversely, you can know if your requests got hijacked into a proxy login page by checking if the first line of the request for something like

<!DOCTYPE....

or

<html....

that’s pretty straightforward and its a classic behaviour for http proxies.

Check this link (With special care on the readTwitterFeed() method). Even if its not for XML it will help you see how a standard RESTful WebService call is done on Android (One way at least). Again, just plug the output from that RESTful call into the filters i described above and then into your favorite XML parser (Assuming the output did pass those sanitation checks).

Bottomline is:
Do not make your own work that much harder. Don’t re-invent the wheel and use what’s available to you in clever ways.

Cheers.