Question

I have an Activity (RecipiesActivity) that is opened by clicking on the “Next” button of the Main Activitiy of my application.

In the RecipiesActivity onCreate, I want to call a webservice in an AsyncTask. For now, since I have not implemented the webservice yet, I am just calling a webservice provided by bitly (but this is irrelevant to my problem).

The problem is that although the webservice gets called and no exception is thrown, a result is return from the doInBackground, but my onPostExecute is not called. I have done some research and I have found the possible reasons as listed below – but none seem to be my case:

• onPostExecute parameters do not match the AsyncTask parameters – in my case they match
• A bug in android that does not allow the AsyncTask to be executed in the UI thread. It is supposadely overcomes by using Class.forName(“android.os.AsyncTask”) – I tried this and did not make any difference
• AsyncTask is not started from the UI thread – in my case I believe it is
• doInBackground does not return – in my case it does, I have stepped through it with the debugger
• @Override is not used before onPostExecute – in my case I am using @Override

The code is below:

public class RecipiesActivity extends Activity {

    private TextView tv;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_recipies); 
        tv = (TextView) findViewById(R.id.Response);

        //Start the WS call in an AsyncTask 
        new CallWS().doInBackground("https://api-ssl.bitly.com/v3/shorten?login=maskedLogin&apiKey=maskedKey&longUrl=http%3A%2F%2Fgoogle.com%2F");          
    }

    private class CallWS extends AsyncTask<String, Integer, String>
    {
        @Override
        protected String doInBackground(String... params) {

            String result = null;
            HttpClient httpClient = new DefaultHttpClient(); 
            HttpContext localContext = new BasicHttpContext(); 
            HttpGet get_request = new HttpGet(params[0]); 
            try
            {
                HttpResponse httpResponse = httpClient.execute(get_request, localContext);
                //int responseCode = httpResponse.getStatusLine().getStatusCode();
                HttpEntity entity = httpResponse.getEntity();
                if (entity != null)
                {
                    InputStream istream = entity.getContent();
                    BufferedReader br = new BufferedReader(new InputStreamReader(istream));

                    try
                    {
                        result = br.readLine();
                    }
                    catch (Exception e)
                    {
                        //TODO Handle the IOException that the readline may throw 
                    }
                    finally
                    {
                        istream.close();
                    }
                }

            }catch (Exception e)
            {
                //TODO Handle the IOException and the ClientProtocolException that the 
                // httpClient.execute can throw
            }
            finally
            {
                httpClient.getConnectionManager().shutdown();
            }
            return result;
        } 

        @Override
        protected void onPostExecute(String result)
        {
            if (result == null)
            {
                tv.setText("The result is NULL");
            }
            else
            {
                tv.setText(result);
            }
        }       
    }
}

Your help is appreceiated,

thanks

Answer 1

Instead of doInBackground(), simply call the execute() method of the AsyncTask. Calling doInBackground() does what it says on the tin: calls doInBackground() (in the same thread) and returns. It won’t call onPostExecute() for you. execute() will start a background thread, call doInBackground() on the background thread, then post the result of doInBackground() to onPostExecute() on the UI thread.