Question

i am building an application for clients to get questions from server and answer it, if the server doesn’t have questions i want to go to new screen and print message that try again in few minutes, getting questions is in AsyncTask , if the server doesn’t have questions , it will sends in the header of the responds, a header isFindAQuestion with the value false, here is the code on client to ensure if false , i print on LogCat and i see the message = false, but my problems that even if i start new activity with the intent, this activity keep working and show me exception and it is null pointer exception because on the onPostExceute will take a parmeter null and try to process it, i put finish() in the end of false statement but doesn’t finish the activity

if (response.getFirstHeader("isFindAQuestion").getValue()
                        .toString().equals("false")) {
                    Log.d("message", "false");
                    Bundle basket = new Bundle();
                    basket.putString("Message", "sorry no enought questions");
                    Intent goToAnswerQuestion = new Intent(AnswerQuestion.this,
                            FinishTime.class);
                    goToAnswerQuestion.putExtras(basket);
                    startActivity(goToAnswerQuestion);
                    finish();

                } 

Edit

is it because AsyncTask is working on thread so if the activity is finished, that thread will keep working? and if so how can i stop that thread?

Answer 1

doInBackground is not executed in the UI thread, but in a separeted thread:

invoked on the background thread immediately after onPreExecute()
finishes executing. This step is used to perform background
computation that can take a long time.

If you want to stop your background operation and perform some activities on the UI thread the better thing is to call cancel() and then perform all the stuff you want in the onCancelled callback wich is executed on the UI thread.

From the AsyncTask documentation:

A task can be cancelled at any time by invoking cancel(boolean).
Invoking this method will cause subsequent calls to isCancelled() to return true. After invoking this method, onCancelled(Object), instead of onPostExecute(Object) will be invoked after doInBackground(Object[]) returns.
To ensure that a task is cancelled as quickly as possible, you should always check the return value of isCancelled() periodically from doInBackground(Object[]), if possible (inside a loop for instance.)

protected void onCancelled (Result result)

Runs on the UI thread after cancel(boolean) is invoked and doInBackground(Object[]) has finished.
The default implementation simply invokes onCancelled() and ignores the result. If you write your own implementation, do not call super.onCancelled(result).