AsyncTask stops application

Question

I'm using AsyncTask in my application, but when it starts, it's like that it never ends. When I'm debugging after doInBackground application freezes and stuck in ThreadPoolExecutor.runWorker(ThreadPoolExecutor$Worker).

Here's the structure of my code

class FetchSymbolInfo extends AsyncTask<String, Void, Document> {

        private Exception exception = null;

        @Override
        protected Document doInBackground(String... params) 
        {
            try 
            {
                Document doc = null;
                //doc = Jsoup.connect(params[0]).get();//application freezes even if I remove this line
                return doc;
            } 
            catch (Exception e) 
            {
                this.exception = e;
                return null;
            }
        }

        @Override
        protected void onPostExecute(Document result) 
        {
            if(exception != null)
        {
            AlertDialog alertDialog;
            alertDialog = new AlertDialog.Builder(null).create();//////////
            alertDialog.setTitle("Error");
            alertDialog.setMessage("Could not fetch from internetd\nPlease check your inernet connection and symbol name.");
            alertDialog.show();
            return;
        }

        Elements valueElement = result.select("div#qwidget_lastsale");
        String valueString = valueElement.toString();
        //getting number from string
        }

        @Override
          protected void onPreExecute() {
          }

        @Override
        protected void onCancelled() {
            super.onCancelled();
        }

        @Override
        protected void onCancelled(Document result) {
            super.onCancelled(result);
        }

        @Override
        protected void onProgressUpdate(Void... values) {
            super.onProgressUpdate(values);
        }

And I'm trying to execute it like this

String url = "url";  //writing an url
FetchSymbolInfo fetch = new FetchSymbolInfo();
fetch.execute(url);

Any ideas? Thank you in advance!

Is this your actual code, or just a skeleton? I don't see anything here that should cause it to hang. It just sends a `null` to `onPostExecute` and stops. — Geobits, Jul 29 '13 at 18:59
It's just a skeleton, but I'm trying my code with the same body of `doInBackground` function as written here and it freezes again — nabroyan, Jul 29 '13 at 19:02
show the code for `@Override protected void onPostExecute(Document result) { if(exception != null) { //print error } //doing some stuff }` — wtsang02, Jul 29 '13 at 19:08
I just edited my post. But problem is that it never reach to `onPostExecute` — nabroyan, Jul 29 '13 at 19:13
@nabroyan Are you sure it doesn't just stop inside that method rather than not reaching? Add `Log.i("onPostExecute", "Started"); to the first line in that method and see if it's outputted in the Logcat — whitfin, Jul 29 '13 at 20:25
@Zackehh9lives I put a breakpoint on the first line of `onPostExcucute` method, and during debugging I never reached to that breakpoint — nabroyan, Jul 30 '13 at 07:53
@nabroyan If it's running on a new thread, does a breakpoint still get caught by the debugger? — whitfin, Jul 30 '13 at 17:15
@Zackehh9lives you're right, as it was another thread breakpoint is not being caught by debugger (as Visual Studio does). — nabroyan, Jul 31 '13 at 06:37
@nabroyan Then use `Log` as I first suggested, that should help you out. Also, `AlertDialog.Builder(context)` is what you need, with context being passed from the calling Activity. — whitfin, Jul 31 '13 at 06:46
@Zackehh9lives I've already tried that and it worked. Now I use `Log` and `context` instead of `null`. Thank you!! — nabroyan, Jul 31 '13 at 06:51

score 1 · Accepted Answer · answered Jul 31 '13 at 07:04

You're trying to create an AlertDialog by providing a null Context. What you need to do is pass a valid Context from the Activity calling the AsyncTask by passing the Context to the constructor of the task and then using that with the Dialog:

class FetchSymbolInfo extends AsyncTask<String, Void, Document> {

private Context parent;

// ...

public FetchSymbolInfo(Context c){
    parent = c;
}

// ...

if(exception != null){
    AlertDialog alertDialog;
    alertDialog = new AlertDialog.Builder(parent).create();
    alertDialog.setTitle("Error");
    alertDialog.setMessage("Could not fetch from internetd\nPlease check your inernet connection and symbol name.");
    alertDialog.show();
    return;
}

Addition: Although not directly related to the question, I think it's important to mention here than if you set a breakpoint in a new thread as the OP did, you won't hit it - you're better off using Log to keep track of entering/exiting methods/code blocks.

score 0 · Answer 2 · answered Jul 29 '13 at 20:23

0

It seams that you should be getting a NPE in.

    Elements valueElement = result.select("div#qwidget_lastsale");

answered Jul 29 '13 at 20:23

Hadriel

159
1
13

Excuse me, what do you mean by saying NPE? – nabroyan Jul 30 '13 at 07:51
@nabroyan NullPointerException – whitfin Jul 30 '13 at 17:14
@Zackehh9lives that's right I returned `null` and `exception` was `null` to and I tried to work with result. And if I an exception occurred`alertDialog = new AlertDialog.Builder(null).create();` line caused NPE. So there was lot of `null` in this piece of code – nabroyan Jul 31 '13 at 06:38

AsyncTask stops application

2 Answers2