AsyncTask停止应用程序

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!

Answer 1

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.

Answer 2

它接缝你应该得到NPE。

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