Develop Reference

Handle AsyncTask if the task completes while the Activity is in the background

I've been using AsyncTasks for a while however, I've recently encountered a scenario where I'm unsure of how to handle correctly. Since I thought it would be a somewhat common scenario I decided to ask the question here.
So, I'm trying to use an AsyncTask to make a simple call to sign a user in to the app. After the call completes, if it succeeds, the user should be taken to another activity. This logic is simple. The problem arrises when the user navigates away from the app before the sign in call returns. In such a case, what should I do in onPostExecute()?
What I've seen some apps do is they continue with the call anyways, as long as the activity is still around, and will launch the next activity. However this creates a weird experience where the user navigates away from the app, then several seconds later, the app just pops back up in their face. Of course, I would like to avoid doing this.
Update
Example code:
public class ExampleActivity extends Activity {
private boolean mIsPaused;
...
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
...
Button btnSignIn = (Button) findViewById(R.id.btn_sign_in);
btnSignIn.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
new SignInTask(ExampleActivity.this).execute();
}
});
...
}
#Override
protected void onPause() {
super.onPause();
mIsPaused = true;
}
#Override
protected void onResume() {
super.onResume();
mIsPaused = false;
}
private boolean isPaused() {
return mIsPaused;
}
...
private static class SignInTask extends AsyncTask<Void, Void, SomeResult> {
private final WeakReference<ExampleActivity> mAct;
public SignInTask(ExampleActivity act) {
mAct = new WeakReference<ExampleActivity>(act);
}
#Override
protected SomeResult doInBackground(Void... params) {
return mApi.signIn(creds);
}
#Override
protected void onPostExecute(SomeResult result) {
if (result.getCode() == OK) {
ExampleActivity act = mAct.get();
if (act != null) {
if (act.isPaused()) {
// do something
} else {
startActivity(new Intent(act, NextActivity.class));
}
} else {
// do something
}
}
}
}
}

made your AsyncTask class as static inner class.

Pretty interesting problem... Going with what you've started by using booleans, you could save the response the Activity receives to the SharedPreferences in the event it is paused, or continue processing normally if it is not. If the Activity later resumes (or is recreated), check whether or not there is a saved response and handle accordingly. I was thinking something along the lines of:
import org.json.JSONObject;
import android.app.Activity;
import android.os.Bundle;
public class TaskActivity extends Activity {
private static final String KEY_RESPONSE_JSON = "returned_response";
private boolean paused = false;
public void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
// don't setup here, wait for onPostResume() to figure out what to do
}
#Override
public void onPostResume(){
super.onPostResume();
paused = false;
if(isSavedResponseAvailable()) processResponse(getSavedResponse());
else setup();
}
#Override
public void onPause(){
paused = true;
super.onPause();
}
private void setup(){
// normal setup
}
public void onReceiveResponse(JSONObject response){
if(paused) setSavedResponse(response);
else processResponse(response);
}
private void processResponse(JSONObject response){
// Continue with processing as if they never left
getSharedPreferences(this.getClass().getName(), 0).edit().clear().commit(); // Clear everything so re-entering won't parse old data
}
private boolean isSavedResponseAvailable(){
return getSavedResponse() != null;
}
private JSONObject getSavedResponse(){
try{
return new JSONObject(getSharedPreferences(this.getClass().getName(), 0).getString(KEY_RESPONSE_JSON, ""));
}
catch(Exception e){ }
return null;
}
private void setSavedResponse(JSONObject response){
getSharedPreferences(this.getClass().getName(), 0).edit().putString(KEY_RESPONSE_JSON, response.toString()).commit();
}
}
Clearly that's assuming your response from the task is JSON, but there's no reason you couldn't extend that to save the data individually and rebuild the necessary response object from the saved preference data.
As far as clean approaches go, though... I give this about a 3/10, but I can't think of anything better (well, other than making the TaskActivity abstract and forcing implementations to override setup(), processResponse(), isResponseAvailable(), getSavedResponse(), and setSavedResponse(), but that would only be mildly better for like a 4/10)

I would suggest putting a try/catch statement in the post execute - as far as I know what would happen in this situation is that you would get some kind of Window Manager exception.
What I would STRONGLY recommend, however, is stopping any async tasks (with the cancel method) on the onPause method, meaning that you won't interrupt them.
http://developer.android.com/reference/android/os/AsyncTask.html#cancel(boolean)
public final boolean cancel (boolean mayInterruptIfRunning)
Added in API level 3
Attempts to cancel execution of this task. This attempt will fail if the task has already completed, already been cancelled, or could not be cancelled for some other reason. If successful, and this task has not started when cancel is called, this task should never run. If the task has already started, then the mayInterruptIfRunning parameter determines whether the thread executing this task should be interrupted in an attempt to stop the task.
Calling this method will result in onCancelled(Object) being invoked on the UI thread after doInBackground(Object[]) returns. Calling this method guarantees that onPostExecute(Object) is never invoked. After invoking this method, you should check the value returned by isCancelled() periodically from doInBackground(Object[]) to finish the task as early as possible.
Parameters
mayInterruptIfRunning true if the thread executing this task should be interrupted; otherwise, in-progress tasks are allowed to complete.
Returns
false if the task could not be cancelled, typically because it has already completed normally; true otherwise
See Also
isCancelled()
onCancelled(Object)

boolean isRunning; //set it to true in onResume, and false in onStop
boolean isWaiting; // set it to true in onPostExecute, if "isRunning" is false
check in onResume whether isWaiting is true, if yes, take user to another screen.

Use the cancel() of AsynchTask class onBackPress() of Activty class
public class ExampleActivity extends Activity {
private boolean mIsPaused;
SignInTask singleTaskObj;
...
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
...
Button btnSignIn = (Button) findViewById(R.id.btn_sign_in);
btnSignIn.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
singleTaskObj = new SignInTask(ExampleActivity.this).execute();
}
});
...
}
#Override
protected void onPause() {
super.onPause();
mIsPaused = true;
}
#Override
protected void onResume() {
super.onResume();
mIsPaused = false;
}
protected void onBackPressed()
{
singleTaskObj.cancel();
}
private boolean isPaused() {
return mIsPaused;
}
...
private static class SignInTask extends AsyncTask<Void, Void, SomeResult> {
private final WeakReference<ExampleActivity> mAct;
public SignInTask(ExampleActivity act) {
mAct = new WeakReference<ExampleActivity>(act);
}
#Override
protected SomeResult doInBackground(Void... params) {
return mApi.signIn(creds);
}
#Override
protected void onPostExecute(SomeResult result) {
if (result.getCode() == OK) {
ExampleActivity act = mAct.get();
if (act != null) {
if (act.isPaused()) {
// do something
} else {
startActivity(new Intent(act, NextActivity.class));
}
} else {
// do something
}
}
}
}
}

Progress Dialog Freezes while switching to another activity

I have two activities. While switching to second activity by intent, it takes 3-4 seconds because it has lots of components with adapters fetching data from SQLite etc. Thus, I want to show a progress dialog while switching.
I have been digging topics for this purpose and tried many of them:
1-) Using AsyncTask on the second activity. It doesn't show the progress dialog as soon as I click on a component to switch to the second activity. It waits for 3-4 seconds and then progress dialog shows up for less then a second which is not user-friendly way.
2-) Using AsyncTask on the first activity. It shows as soon as I click on that component but the progress wheel doesn't spin. The progress dialog freezes.
3-) Using AsyncTask onStart() method on the second activity. This results as the first way.
The code below implements the second way above, using AsyncTask on the first activity.
public void toVisitRegister(Event event) { //Switching to the second activity
new startingThread().execute();
Intent toVisitRegister = new Intent(MainCalendar.this, VisitRegister.class);
startActivity(toVisitRegister);
finish();
}
And here is the AsyncTask
public class startingThread extends AsyncTask<String, String, String> {
#Override
protected void onPreExecute() {
super.onPreExecute();
startingProgress = new ProgressDialog(MainCalendar.this);
startingProgress.setTitle("Visit Register");
startingProgress.setMessage("Initializing...");
startingProgress.show();
}
#Override
protected String doInBackground(String... params) {
return null;
}
#Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
if(MainCalendar.this.startingProgress != null) {
MainCalendar.this.startingProgress.dismiss();
}
}
}
I also tried to call startActivity in onPostExecute, but it didn't work. Therefore, I am waiting for your opinions and suggessions about this issue. Any help will be appreciated.
Thanks.

I also tried to call startActivity in onPostExecute,
Pass the Activity context to startingThread AsyncTask and put your start activity code in onPostExecute() of AsyncTask.
#Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
if(MainCalendar.this.startingProgress != null) {
MainCalendar.this.startingProgress.dismiss();
Intent toVisitRegister = new Intent(MainCalendar.this, VisitRegister.class);
mContext.startActivity(toVisitRegister);
mContext.finish();
}
}
Here mContext is the Context of your current MainCalendar Activity.

Looking at your implementation, the AsyncTask wont have time to work because you will be jumping to the next Activity right away. Try calling the next activity in PostExecute().
I also tried to call startActivity in onPostExecute, but it didn't work.
Did you did it like this:
public void toVisitRegister(Event event) { //Switching to the second activity
new startingThread().execute();
}
public class startingThread extends AsyncTask<String, String, String> {
#Override
protected void onPreExecute() {
super.onPreExecute();
startingProgress = new ProgressDialog(MainCalendar.this);
startingProgress.setTitle("Visit Register");
startingProgress.setMessage("Initializing...");
startingProgress.show();
}
#Override
protected String doInBackground(String... params) {
return null;
}
#Override
protected void onPostExecute(String result) {
if(MainCalendar.this.startingProgress != null) {
MainCalendar.this.startingProgress.dismiss();
}
Intent toVisitRegister = new Intent(MainCalendar.this, VisitRegister.class);
startActivity(toVisitRegister);
finish();
}
}

Android Update Current Activity From Background Thread

My application has a refresh button on the main activity. When the user presses that button, a new thread is created which starts updating the SQLite database. When this thread started, user could possibly get into another activies of the application.
The problem is these other activities(ListActivity) should be updated according to the DB when that background thread is completed. How could I provide that. I tried getting current task with ActivityManager but It requires extra permission which I dont want.

Edit:
Sorry seems I misunderstood you. Please take a look at the following code, it is similar to Chinaski's (you just use an interface for the callback methods) but I added a bit more to ensure you know how to use it in a way that will avoid memory leaks.
Note how the activity detaches during onDestroy -- alternatively you could use a WeakReference, however these days you'd use a Fragment with setRetainInstance(true) and completely avoid the detaching/attaching as the fragment would be retained.
MyAsyncTask
public class MyAsyncTask extends AsyncTask<Void, Void, Void> {
private Callback mCallback;
private boolean mIsComplete = false;
private boolean mHasCallbackBeenCalled = false;
public MyBackgroundTask(Callback callback) {
mCallback = callback;
}
/** Only safe to call this from the UI thread */
public void attach(Callback callback) {
mCallback = callback;
if (mIsComplete && !mHasCallbackBeenCalled) {
fireCallback();
}
}
/** Only safe to call this from the UI thread */
public void detach() {
mCallback = callback;
}
#Override
public void doInBackground() {
// do the heavy stuff here
return null;
}
#Override
public void onPostExecute(Void result) {
mIsComplete = true;
fireCallback();
}
private void fireCallback() {
if (mCallback != null) {
mCallback.callbackMethod();
mHasCallbackBeenCalled = true;
}
}
public static interface Callback {
public void callbackMethod();
}
}
MyActivity
public class MyActivity extends Activity implements MyAsyncTask.Callback {
private MyAsyncTask mTask;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Check for a retained task after a configuration change
// e.g. a rotation
if (getLastNonConfigurationInstance() != null) {
mTask = (MyAsyncTask) getLastNonConfigurationInstance();
// Re-attach the task
mTask.attach(this);
}
}
#Override
public void onDestroy() {
// Detach from task to avoid memory leak
if (mTask != null) {
mTask.detach();
}
super.onDestroy();
}
#Override
public Object onRetainNonConfigurationInstance() {
// Retain the async task duration a rotation
return mTask;
}
/** Callback method */
#Override
public void callbackMethod() {
// Do something here
}
}

You could make a singleton in which you will have your thread and a queue of "tasks". When a task is finished, you check / launch the next task, and when you add a task, you launch it, or add it in the queue if a task is already running.
I don't say this is the best solution, but it's one.

AsyncTask crashing on screen rotation [duplicate]

I read a lot on how to save my instance state or how to deal with my activity getting destroyed during screen rotation.
There seem to be a lot of possibilities but I haven't figured out which one works best for retrieving results of an AsyncTask.
I have some AsyncTasks that are simply started again and call the isFinishing() method of the activity and if the activity is finishing they wont update anything.
The problem is that I have one Task that does a request to a web service that can fail or succeed and restarting the task would result in a financial loss for the user.
How would you solve this? What are the advantages or disadvantages of the possible solutions?

You can check out how I handle AsyncTasks and orientation changes at code.google.com/p/shelves. There are various ways to do it, the one I chose in this app is to cancel any currently running task, save its state and start a new one with the saved state when the new Activity is created. It's easy to do, it works well and as a bonus it takes care of stopping your tasks when the user leaves the app.
You can also use onRetainNonConfigurationInstance() to pass your AsyncTask to the new Activity (be careful about not leaking the previous Activity this way though.)

This is the most interesting question I've seen regarding to Android!!! Actually I've been already looking for the solution during the last months. Still haven't solved.
Be careful, simply overriding the
android:configChanges="keyboardHidden|orientation"
stuff is not enough.
Consider the case when user receives a phone call while your AsyncTask is running. Your request is already being processed by server, so the AsyncTask is awaiting for response. In this moment your app goes in background, because the Phone app has just come in foreground. OS may kill your activity since it's in the background.

My first suggestion would be to make sure you actually need your activity to be reset on a screen rotation (the default behavior). Every time I've had issues with rotation I've added this attribute to my <activity> tag in the AndroidManifest.xml, and been just fine.
android:configChanges="keyboardHidden|orientation"
It looks weird, but what it does it hand off to your onConfigurationChanged() method, if you don't supply one it just does nothing other than re-measure the layout, which seems to be a perfectly adequate way of handling the rotate most of the time.

Why don't you always keep a reference to the current AsyncTask on the Singleton provided by Android?
Whenever a task starts, on PreExecute or on the builder, you define:
((Application) getApplication()).setCurrentTask(asyncTask);
Whenever it finishes you set it to null.
That way you always have a reference which allows you to do something like, onCreate or onResume as appropriated for your specific logic:
this.asyncTaskReference = ((Application) getApplication()).getCurrentTask();
If it's null you know that currently there is none running!
:-)

The most proper way to this is to use a fragment to retain the instance of the async task, over rotations.
Here is a link to very simple example making it easy to follow integrate this technique into your apps.
https://gist.github.com/daichan4649/2480065

In Pro android 4. author has suggest a nice way, that you should use weak reference.
Weak reference note

To my point of view, it's better to store asynctask via onRetainNonConfigurationInstance decoupling it from the current Activity object and binding it to a new Activity object after the orientation change. Here I found a very nice example how to work with AsyncTask and ProgressDialog.

Android : background processing/Async Opeartion with configuration change
To maintain the states of async opeartion during background process:
you can take an help of fragments.
See the following steps :
Step 1: Create a headerless fragment let say background task and add a private async task class with in it.
Step 2 (Optional Step): if you want to put a loading cursor on top of your activity use below code:
Step 3: In your main Activity implement BackgroundTaskCallbacks interface defined in step 1
class BackgroundTask extends Fragment {
public BackgroundTask() {
}
// Add a static interface
static interface BackgroundTaskCallbacks {
void onPreExecute();
void onCancelled();
void onPostExecute();
void doInBackground();
}
private BackgroundTaskCallbacks callbacks;
private PerformAsyncOpeation asyncOperation;
private boolean isRunning;
private final String TAG = BackgroundTask.class.getSimpleName();
/**
* Start the async operation.
*/
public void start() {
Log.d(TAG, "********* BACKGROUND TASK START OPERATION ENTER *********");
if (!isRunning) {
asyncOperation = new PerformAsyncOpeation();
asyncOperation.execute();
isRunning = true;
}
Log.d(TAG, "********* BACKGROUND TASK START OPERATION EXIT *********");
}
/**
* Cancel the background task.
*/
public void cancel() {
Log.d(TAG, "********* BACKGROUND TASK CANCEL OPERATION ENTER *********");
if (isRunning) {
asyncOperation.cancel(false);
asyncOperation = null;
isRunning = false;
}
Log.d(TAG, "********* BACKGROUND TASK CANCEL OPERATION EXIT *********");
}
/**
* Returns the current state of the background task.
*/
public boolean isRunning() {
return isRunning;
}
/**
* Android passes us a reference to the newly created Activity by calling
* this method after each configuration change.
*/
public void onAttach(Activity activity) {
Log.d(TAG, "********* BACKGROUND TASK ON ATTACH ENTER *********");
super.onAttach(activity);
if (!(activity instanceof BackgroundTaskCallbacks)) {
throw new IllegalStateException(
"Activity must implement the LoginCallbacks interface.");
}
// Hold a reference to the parent Activity so we can report back the
// task's
// current progress and results.
callbacks = (BackgroundTaskCallbacks) activity;
Log.d(TAG, "********* BACKGROUND TASK ON ATTACH EXIT *********");
}
public void onCreate(Bundle savedInstanceState) {
Log.d(TAG, "********* BACKGROUND TASK ON CREATE ENTER *********");
super.onCreate(savedInstanceState);
// Retain this fragment across configuration changes.
setRetainInstance(true);
Log.d(TAG, "********* BACKGROUND TASK ON CREATE EXIT *********");
}
public void onDetach() {
super.onDetach();
callbacks = null;
}
private class PerformAsyncOpeation extends AsyncTask<Void, Void, Void> {
protected void onPreExecute() {
Log.d(TAG,
"********* BACKGROUND TASK :-> ASYNC OPERATION :- > ON PRE EXECUTE ENTER *********");
if (callbacks != null) {
callbacks.onPreExecute();
}
isRunning = true;
Log.d(TAG,
"********* BACKGROUND TASK :-> ASYNC OPERATION :- > ON PRE EXECUTE EXIT *********");
}
protected Void doInBackground(Void... params) {
Log.d(TAG,
"********* BACKGROUND TASK :-> ASYNC OPERATION :- > DO IN BACKGROUND ENTER *********");
if (callbacks != null) {
callbacks.doInBackground();
}
Log.d(TAG,
"********* BACKGROUND TASK :-> ASYNC OPERATION :- > DO IN BACKGROUND EXIT *********");
return null;
}
protected void onCancelled() {
Log.d(TAG,
"********* BACKGROUND TASK :-> ASYNC OPERATION :- > ON CANCEL ENTER *********");
if (callbacks != null) {
callbacks.onCancelled();
}
isRunning = false;
Log.d(TAG,
"********* BACKGROUND TASK :-> ASYNC OPERATION :- > ON CANCEL EXIT *********");
}
protected void onPostExecute(Void ignore) {
Log.d(TAG,
"********* BACKGROUND TASK :-> ASYNC OPERATION :- > ON POST EXECUTE ENTER *********");
if (callbacks != null) {
callbacks.onPostExecute();
}
isRunning = false;
Log.d(TAG,
"********* BACKGROUND TASK :-> ASYNC OPERATION :- > ON POST EXECUTE EXIT *********");
}
}
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
setRetainInstance(true);
}
public void onStart() {
super.onStart();
}
public void onResume() {
super.onResume();
}
public void onPause() {
super.onPause();
}
public void onStop() {
super.onStop();
}
public class ProgressIndicator extends Dialog {
public ProgressIndicator(Context context, int theme) {
super(context, theme);
}
private ProgressBar progressBar;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
requestWindowFeature(Window.FEATURE_NO_TITLE);
setContentView(R.layout.progress_indicator);
this.setCancelable(false);
progressBar = (ProgressBar) findViewById(R.id.progressBar);
progressBar.getIndeterminateDrawable().setColorFilter(R.color.DarkBlue, android.graphics.PorterDuff.Mode.SCREEN);
}
#Override
public void show() {
super.show();
}
#Override
public void dismiss() {
super.dismiss();
}
#Override
public void cancel() {
super.cancel();
}
public class MyActivity extends FragmentActivity implements BackgroundTaskCallbacks,{
private static final String KEY_CURRENT_PROGRESS = "current_progress";
ProgressIndicator progressIndicator = null;
private final static String TAG = MyActivity.class.getSimpleName();
private BackgroundTask task = null;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(//"set your layout here");
initialize your views and widget here .............
FragmentManager fm = getSupportFragmentManager();
task = (BackgroundTask) fm.findFragmentByTag("login");
// If the Fragment is non-null, then it is currently being
// retained across a configuration change.
if (task == null) {
task = new BackgroundTask();
fm.beginTransaction().add(task, "login").commit();
}
// Restore saved state
if (savedInstanceState != null) {
Log.i(TAG, "KEY_CURRENT_PROGRESS_VALUE ON CREATE :: "
+ task.isRunning());
if (task.isRunning()) {
progressIndicator = new ProgressIndicator(this,
R.style.TransparentDialog);
if (progressIndicator != null) {
progressIndicator.show();
}
}
}
}
#Override
protected void onPause() {
// TODO Auto-generated method stub
super.onPause();
}
#Override
protected void onSaveInstanceState(Bundle outState) {
// save the current state of your operation here by saying this
super.onSaveInstanceState(outState);
Log.i(TAG, "KEY_CURRENT_PROGRESS_VALUE ON SAVE INSTANCE :: "
+ task.isRunning());
outState.putBoolean(KEY_CURRENT_PROGRESS, task.isRunning());
if (progressIndicator != null) {
progressIndicator.dismiss();
progressIndicator.cancel();
}
progressIndicator = null;
}
private void performOperation() {
if (!task.isRunning() && progressIndicator == null) {
progressIndicator = new ProgressIndicator(this,
R.style.TransparentDialog);
progressIndicator.show();
}
if (task.isRunning()) {
task.cancel();
} else {
task.start();
}
}
#Override
protected void onDestroy() {
super.onDestroy();
if (progressIndicator != null) {
progressIndicator.dismiss();
progressIndicator.cancel();
}
progressIndicator = null;
}
#Override
public void onPreExecute() {
Log.i(TAG, "CALLING ON PRE EXECUTE");
}
#Override
public void onCancelled() {
Log.i(TAG, "CALLING ON CANCELLED");
if (progressIndicator != null) {
progressIndicator.dismiss();
progressIndicator.cancel();
}
public void onPostExecute() {
Log.i(TAG, "CALLING ON POST EXECUTE");
if (progressIndicator != null) {
progressIndicator.dismiss();
progressIndicator.cancel();
progressIndicator = null;
}
}
#Override
public void doInBackground() {
// put your code here for background operation
}
}

One thing to consider is whether the result of the AsyncTask should be available only to the activity that started the task. If yes, then Romain Guy's answer is best. If it should be available to other activities of your application, then in onPostExecute you can use LocalBroadcastManager.
LocalBroadcastManager.getInstance(getContext()).sendBroadcast(new Intent("finished"));
You will also need to make sure that activity correctly handles situation when broadcast is sent while activity is paused.

Have a look at this post. This Post involves AsyncTask performing long running operation and memory leak when screen rotation happens both in one sample application. The sample app is available on the source forge

My solution.
In my case i've got a chain of AsyncTasks with the same context. Activity had an access only to first one. To cancel any running task i did the following:
public final class TaskLoader {
private static AsyncTask task;
private TaskLoader() {
throw new UnsupportedOperationException();
}
public static void setTask(AsyncTask task) {
TaskLoader.task = task;
}
public static void cancel() {
TaskLoader.task.cancel(true);
}
}
Task doInBackground():
protected Void doInBackground(Params... params) {
TaskLoader.setTask(this);
....
}
Activity onStop() or onPause():
protected void onStop() {
super.onStop();
TaskLoader.cancel();
}

#Override
protected void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
final AddTask task = mAddTask;
if (task != null && task.getStatus() != UserTask.Status.FINISHED) {
final String bookId = task.getBookId();
task.cancel(true);
if (bookId != null) {
outState.putBoolean(STATE_ADD_IN_PROGRESS, true);
outState.putString(STATE_ADD_BOOK, bookId);
}
mAddTask = null;
}
}
#Override
protected void onRestoreInstanceState(Bundle savedInstanceState) {
super.onRestoreInstanceState(savedInstanceState);
if (savedInstanceState.getBoolean(STATE_ADD_IN_PROGRESS)) {
final String id = savedInstanceState.getString(STATE_ADD_BOOK);
if (!BooksManager.bookExists(getContentResolver(), id)) {
mAddTask = (AddTask) new AddTask().execute(id);
}
}
}

you can also add
android:configChanges="keyboardHidden|orientation|screenSize"
to your manifest example i hope it help
<application
android:name=".AppController"
android:allowBackup="true"
android:icon="#mipmap/ic_launcher"
android:label="#string/app_name"
android:roundIcon="#mipmap/ic_launcher_round"
android:supportsRtl="true"
android:configChanges="keyboardHidden|orientation|screenSize"
android:theme="#style/AppTheme">

Android Why does my app Force to close?

I admit, I'm new at this whole Android stuff. I am trying to make an app but randomly I get Force close errors and I really don't know why. My application has many activities, none of them finish() when I start a new one. I get data from the web (via web services and direct image downloading) and I use AsyncTask a lot. Most of the time it crashes on the asynctask. Here is a sample on how I do things:
private BackTask backTask;
Activity ctx = this;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.trackslist);
backTask = new BackTask();
backTask.execute();
}
protected class BackTask extends AsyncTask<Context, String, myObject>
{
#Override
protected myObject doInBackground(Context... params)
{
try{
if (hasInternet(ctx)==true)
{
//access the web SERVICE here
//initialize myObject WITH result FROM the web
return myObject
}
else
{
return null
}
}catch(Exception ex){
return null;
}
}
#Override
protected void onPreExecute()
{
super.onPreExecute();
}
#Override
protected void onProgressUpdate(String... values)
{
super.onProgressUpdate(values);
}
#Override
protected void onCancelled()
{
super.onCancelled();
}
#Override
protected void onPostExecute( myObject result )
{
super.onPostExecute(result);
if (result==null || result.isEmpty())
{
//no valid result, show a message
}
else
{
//result valid do something with it
}
}
}
#Override
public void onPause()
{
if (backTask!=null && ! backTask.isCancelled())
{
backTask.cancel(true);
}
super.onPause();
}
public void btnStartOnClick(View target) {
Intent intent = new Intent(this, MyNewActivity.class);
startActivity(intent);
}
When the activity gets onPause() the task is being canceled. I am not sure what happens during the try/catch if a error appears, from what I've did, it should return null, but I think here I miss something. As I said before, randomly I get a force close even if I am on another Activity. This is really frustrating as I can't offer a app that has this behavior. So, what am I doing wrong ?

There is problem in your code. I have corrected as follows: You find I have added this while calling async task.
Your async task accept context as argument and you was not passing that.
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.trackslist);
backTask = new BackTask();
backTask.execute(this);
}

You need to ask inside your AsyncTask class for isCancelled() and then decide what to do.
Check this question. It has a good explanation by Romain Guy:
You can stop an AsyncTask. If you call
cancel(true), an interrupt will be
sent to the background thread, which
may help interruptible tasks.
Otherwise, you should simply make sure
to check isCancelled() regularly in
your doInBackground() method. You can
see examples of this at
code.google.com/p/shelves.