Develop Reference

How to implement a callback in a Fragment starting a Thread?

I try to close a ProgressDialog via Callback from Thread to fragment, but I don't know which reference I need to pass.
Some where in my Fragment I do the following:
c_thread_connectToDevice = new c_Thread_ConnectToDevice(UserSelectedDevice,
sFinalDonglePassword, getActivity());
if(UserSelectedDevice != null){
c_thread_connectToDevice.start();
mProgessDialog.setTitle(R.string.ProgressDialog_Fragmentsetpassword_Title);
mProgessDialog.setMessage(getResources().getString(R.string.ProgressDialog_Fragmentsetpassword_Message));
mProgessDialog.setIndeterminate(true);
mProgessDialog.show();
The Callback is:
public void dismissProgressDialog(){
mProgessDialog.dismiss();
if(!c_thread_connectToDevice.isbConnectionState()){
tv_Fragmentsetpassword_userhint.setTextColor(getResources().getColor(R.color.Mercedes_RED, null));
tv_Fragmentsetpassword_userhint.setText(R.string.tv_Fragmentsetpassword_ConnectionFailed);
}else {
tv_Fragmentsetpassword_userhint.setText(R.string.tv_Fragmentsetpassword_ConnectionSucces);
tv_Fragmentsetpassword_userhint.setTextColor(getResources().getColor(R.color.Mercedes_GREEN, null));
}
}
In my Thread the I use the following Code:
private WeakReference<Activity> weakReference;
...
dismissProgressDialog();
...
private void dismissProgressDialog(){
Activity activity = weakReference.get();
activity.dismissProgressDialog();
}
I know this could not work. But what is the right thing to pass?

What #Zach Bublil told me, brought me to this solution.
private Handler handler = new Handler(Looper.getMainLooper());
c_thread_connectToDevice = new c_Thread_ConnectToDevice(UserSelectedDevice, sFinalDonglePassword, c_Fragment_RoutineStartConnection_setpassword.this);
if(UserSelectedDevice != null){
c_thread_connectToDevice.start();
mProgessDialog = new ProgressDialog(getContext());
mProgessDialog.setTitle(R.string.ProgressDialog_Fragmentsetpassword_Title);
mProgessDialog.setMessage(getResources().getString(R.string.ProgressDialog_Fragmentsetpassword_Message));
mProgessDialog.setIndeterminate(true);
mProgessDialog.show();
CallBack
public void dismissProgressDialog(){
mProgessDialog.dismiss();
handler.post(new Runnable() {
#Override
public void run() {
if(!c_thread_connectToDevice.isbConnectionState()){
tv_Fragmentsetpassword_userhint.setTextColor(getResources().getColor(R.color.Mercedes_RED, null));
tv_Fragmentsetpassword_userhint.setText(R.string.tv_Fragmentsetpassword_ConnectionFailed);
}else {
tv_Fragmentsetpassword_userhint.setText(R.string.tv_Fragmentsetpassword_ConnectionSucces);
tv_Fragmentsetpassword_userhint.setTextColor(getResources().getColor(R.color.Mercedes_GREEN, null));
}
}
});
InsideFragment
private c_Thread_ConnectedToBluetoothDevice c_thread_connectedToBluetoothDevice;
public c_Thread_ConnectToDevice(BluetoothDevice device, String sFinalDonglePassword, c_Fragment_RoutineStartConnection_setpassword reference) {
this.mBluetoothDevice = device;
this.sFinalDonglePassword =sFinalDonglePassword;
this.reference = reference;
}
...
dismissProgressDialog();
...
private void dismissProgressDialog(){
reference.dismissProgressDialog();
}
What is difficult for me to understand is, why I need to run the callback Text editions on mainthread. If I don't do that there is an exception to "Only the original thread creating the view..." but this is maybe caused by
tools:context=".c_RoutineStartConnection"
which I used in the Fragment layout for better usability.

java.lang.IllegalStateException:Make sure the content of your adapter is not modified from a background thread, but only from the UI thread

java.lang.IllegalStateException: The content of the adapter has changed but ListView did not receive a notification. Make sure the content of your adapter is not modified from a background thread, but only from the UI thread. Make sure your adapter calls notifyDataSetChanged() when its content changes. [in ListView(2131296513, class xyz.ScrollDetectableListView) with Adapter(class android.widget.HeaderViewListAdapter)]
I am getting above exception sometimes while scrolling through the dynamic listview and then clicking on item.I researched a lot but unable to find the exact reason that why i am getting this error sometimes and how it can be resolved?
private ScrollDetectableListView mFListView;
public FAdapter mFAdapter;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_feed_view, container, false);
View headerView = getActivity().getLayoutInflater().inflate(R.layout.view_feed_header, null);
try{
mFListView = (ScrollDetectableListView) rootView.findViewById(R.id.feed_list_view);
mFContainer = (SwipeRefreshLayout) rootView.findViewById(R.id.feed_container);
mFListView.addHeaderView(headerView);
mFListView.setEmptyView(rootView.findViewById(R.id.empty_view));
mFContainer.setColorSchemeResources(R.color.green, R.color.pink, R.color.fbcolor,
R.color.instagramcolor, R.color.googlecolor, R.color.flickrcolor);
mFView = getActivity().getLayoutInflater().inflate(R.layout.view_footer, null);
ImageView rotateImageView = (ImageView) mFooterView.findViewById(R.id.spinner);
Animation rotation = AnimationUtils.loadAnimation(getActivity(), R.anim.rotate);
rotation.setFillAfter(false);
rotateImageView.startAnimation(rotation);
mFContainer.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
#Override
public void onRefresh()
{
initializeFListView();
}
});
initializeFListView();
mProgressDialog.setVisibility(View.VISIBLE);
mHActivity.setDataChangedListener(new DataChangedListener() {
#Override
public void onDataChanged() {
mFContainer.setRefreshing(true);
mProgressDialog.setVisibility(View.GONE);
initializeFListView();
}
});
}catch(Exception e){}
return rootView;
}
public void initializeFListView()
{
FApi.getTrending(getActivity(), xyz, new APIResponseListener() {
#Override
public void onResponse(Object response) {
setFeedAdapter((List<Video>) response);
}
#Override
public void onError(VolleyError error) {
if (error instanceof NoConnectionError) {
String errormsg = getResources().getString(R.string.no_internet_error_msg);
Toast.makeText(getActivity(), errormsg, Toast.LENGTH_LONG).show();
}
}
});
}
private void setFAdapter(List<Video> response)
{try {
List<Video> videos = response;
mFAdapter = new FAdapter(getActivity(), videos, mProfileClickListener, mCommentClickListener);
mFListView.setOnScrollListener(new EndlessScrollListenerFeedView(getActivity(), mFListView, mFView, mFAdapter, videos, mFType, ""));
mFListView.setAdapter(mFAdapter);
mProgressDialog.setVisibility(View.GONE);
if (mFContainer.isRefreshing()) {
mFContainer.setRefreshing(false);
}
if (mFAdapter.getCount() < mCount) {
mFView.setVisibility(View.GONE);
mFListView.removeFooterView(mFooterView);
}
}catch(Exception e){}
}
}

My suggestion try to set ur list adapter on UI Thread,,,
private void setFAdapter(List<Video> response)
{
try {
List<Video> videos = response;
mFAdapter = new FAdapter(getActivity(), videos, mProfileClickListener, mCommentClickListener);
mFListView.setOnScrollListener(new EndlessScrollListenerFeedView(getActivity(), mFListView, mFView, mFAdapter, videos, mFType, ""));
runOnUiThread(new Runnable() {
#Override
public void run() {
// TODO Auto-generated method stub
mFListView.setAdapter(mFAdapter);
}
});
mProgressDialog.setVisibility(View.GONE);
if (mFContainer.isRefreshing()) {
mFContainer.setRefreshing(false);
}
if (mFAdapter.getCount() < mCount) {
mFView.setVisibility(View.GONE);
mFListView.removeFooterView(mFooterView);
}
}catch(Exception e){}
}
}

Keep one singleton class object in hand. So that you can synchronize two thread on it. Care to be taken to not to block the ui thread.
Reduce number of interfaces to only one method to start preparing data for your list and only one method to call your notifydatasetchanged/setAdapter on list.
Means there should be only one method like prepareData() which will be executed by a background thread. synchronise this method on your singleton object.
MyListAdaper adapter = null;
// Call this from a background thread
public void prepareData() {
synchronized (SingleTonProvider.getInstance()) {
List<AnyDataTypeYouWant> data = null;
// populate data here by your application logic.
adapter = new MyListAdaper(data);
}
}
And have only one method to refresh list.
// Also Call this from a background thread only
public void refreshList() {
synchronized (SingleTonProvider.getInstance()) {
runOnUiThread(new Runnable() {
#Override
public void run() {
mFListView.setAdapter(adapter);
}
});
}
}
have no other code on any place to prepare data and set data on list.
Call the methods I mentioned from a background thread only.
I just gave general solution to your problem. You have to work on your specific case by yourself.

Appending ListView from onScrollListener

I am trying to update my listview to make an "endless scroll". What happens is that the first 40 results load fine, when i get to the bottom of the scroll, next 40 results replace the first 40...
What I want is for second set of 40 results to add to the first 40 so I have an endless list and ability to scroll back to the beginning of the list.
I am posting my code below. Thank you!
public class SearchResults extends Activity implements BannerAdListener, OnScrollListener{
private LinearLayout bottomNav;
private ListView ringtoneList;
private int start = 0, num = 40, curPage = 1;
private Handler handler = new Handler();
private ProgressDialog progressDialog = null;
private ArrayList<Ringtone> ringtones;
private MoPubView moPubView;
private String searchString;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Bundle extras = getIntent().getExtras();
if (extras == null) {
// no search string defined
finish();
} else {
searchString = extras.getString("search_string");
}
setContentView(R.layout.search_results);
ringtoneList = (ListView)findViewById(R.id.ringtone_list);
ringtoneList.setOnItemClickListener(new AdapterView.OnItemClickListener() {
#Override
public void onItemClick(AdapterView<?> av, View view, int position, long id) {
Intent i = new Intent(SearchResults.this, RingtoneView.class);
i.putExtra("ringtone", ringtones.get(position));
startActivity(i);
}
});
performSearch();
moPubView = (MoPubView) findViewById(R.id.adview);
moPubView.setAdUnitId(Utils.MoPubBannerId);
moPubView.loadAd();
moPubView.setBannerAdListener(this);
ringtoneList.setOnScrollListener(this);
}
public void onScroll(AbsListView view, int firstVisible, final int visibleCount, int totalCount) {
Log.i("List", "firstVisible="+firstVisible+" visibleCount="+visibleCount+" totalCount="+totalCount);
boolean loadMore = firstVisible + visibleCount >= totalCount;
if(loadMore) {
Log.i("List", "Loading More Results");
curPage++;
start = num * (curPage-1);
new Thread() {
public void run() {
ringtones = Utils.search(start, num, searchString);
if (ringtones != null && ringtones.size() > 0) {
handler.post(new Runnable() {
public void run() {
ringtoneList.setAdapter(new RingtoneRowAdapter(SearchResults.this, ringtones));
}
});
} else {
handler.post(new Runnable() {
public void run() {
new AlertDialog.Builder(SearchResults.this)
.setTitle(getResources().getString(R.string.context_info)).setMessage(getResources().getString(R.string.context_noresult))
.setPositiveButton(getResources().getString(R.string.context_ok), null).show();
}
});
}
}
}
.start();
}
}
public void onScrollStateChanged(AbsListView v, int s) { }
private void performSearch() {
progressDialog = ProgressDialog.show(SearchResults.this, getResources().getString(R.string.loading_message), getResources().getString(R.string.loading_search), true);
new Thread() {
public void run() {
ringtones = Utils.search(start, num, searchString);
if (ringtones != null && ringtones.size() > 0) {
updateList();
} else {
handler.post(new Runnable() {
public void run() {
new AlertDialog.Builder(SearchResults.this)
.setTitle(getResources().getString(R.string.context_info)).setMessage(getResources().getString(R.string.context_noresult))
.setPositiveButton(getResources().getString(R.string.context_ok), null).show();
ringtoneList.setVisibility(View.INVISIBLE);
bottomNav.setVisibility(View.INVISIBLE);
}
});
}
progressDialog.dismiss();
}
}.start();
}
private void updateList() {
handler.post(new Runnable() {
public void run() {
//Log.d("search", "ringtones.size() " + ringtones.size());
ringtoneList.setVisibility(View.VISIBLE);
ringtoneList.setAdapter(new RingtoneRowAdapter(SearchResults.this, ringtones));
}
});
}
}
Please help! Thank you!

While I can't be 100% sure, I think your problem has to do with the fact that you're setting a new adapter that only has the section of ringtones that in loads. It probably has to do with this snippet:
ringtones = Utils.search(start, num, searchString);
if (ringtones != null && ringtones.size() > 0) {
handler.post(new Runnable() {
public void run() {
ringtoneList.setAdapter(new RingtoneRowAdapter(SearchResults.this, ringtones));
}
});
}
Instead of putting an entirely new array of ringtones, you should add on to the one you already have. Your ringtones variable is already an instance variable, so I'm sure if you changed this line:
ringtones = Utils.search(start, num, searchString);
to the following:
ringtones.addAll(Utils.search(start, num, searchString));
It might fix your problem.

Your code is a little bit messy, but your updateList method is creating a NEW RingtoneRowAdapter. You should ADD items to the list and call
mRingtoneRowAdapter.notifyDatasetChanged();
That will tell the adapter to get new views (if needed) along with a lot of internal stuff happening at Adapter's level. So it's kinda:
private void updateList() {
handler.post(new Runnable() {
public void run() {
if ( mAdapter == null ) {
mAdapter = new RingtoneRowAdapter(SearchResults.this, ringtones);
ringtoneList.setAdapter(mAdapter);
} else {
mAdapter.notifyDataSetChanged();
}
ringtoneList.setVisibility(View.VISIBLE);
}
});
}
And of course, as already suggested, don't init your ringtones array all the time. Just add data to it.
You don't need (most of the times) to hide the list, you can add in your layout, any View (including a full Layout!) with an id of:
android:id="#android:id/empty"
And if your ListView has an id of android:id="#id/android:list", and you're in a ListFragment or ListActivity, then when the list is empty, the "empty" layout will be shown (which can be a dummy view if you don't want to see it).
Just suggestions :)
UPDATE: For your null, I see that the logic is a little bit weird and since we don't know the requirements for your app (i.e. what to do if there are no results, what to do if the results are invalid, etc.) I'll assume you just want to make sure it works and deal with that later.
So with that in mind, I see two problems.
I assume your Utils.search method can return null, because you're checking for it. To me that feels strange, I'd rather return an empty array indicating that the search produced no results; that little remark aside, you are not checking (or we don't know because we haven't seen the source for your search method), if the searchString is null or not.
You haven't provided a stack trace, so we can't tell where the null is happening (either inside search or ?)
A quick solution would be to check for null before searching… I would personally do this INSIDE the search function.
Something like:
public ArrayList<Ringtone> search(final int start, final int num, final String searchString) {
if ( searchString == null ) {
//DECIDE WHAT YOU WANT TO DO, EITHER:
return null;
// OR YOU CAN RETURN AN EMPTY ARRAY
return new ArrayList<Ringtone>();
}
// You should check for these (change according to your rules)
if (start < 0 ) {
start = 0; // protect yourself from bad data.
}
if ( num < 0 ) {
num = 0;
}
/// THE REST OF YOUR search FUNCTION
return <your array>
}
Now another thing is that you may want the search to return incremental results (so you can ADD them to your array (instead of returning a new array every time). For that, as already suggested, use the addAll trick, but then, DON'T return null, return an new empty array, so there's no harm done if there's nothing else to add.

Load data when user stops swiping in fragmentviewpager in android?

Load fragment when user stops swiping instead of previous,current,next pattern in fragmentviewpager in android?
Load single fragment at a time in fragmentviewpager instead of multiple.

On Fragment Load FragmentViewPager sets setUserVisibleHint to true of current fragment. Through that we can put delay in loading fragment in FragmentViewPager. In Below code i have put delay of 1000 ms.
#Override
public boolean getUserVisibleHint() {
boolean isVisible = super.getUserVisibleHint();
return isVisible;
}
public Runnable handleDelays = new Runnable() {
#Override
public void run() {
if (getUserVisibleHint()) {
// Application Logic
}
}
};
private Handler pagerHandler;
#Override
public void setUserVisibleHint(boolean isVisibleToUser) {
super.setUserVisibleHint(isVisibleToUser);
if (this.isVisible()) {
if (!isVisibleToUser) {
pagerHandler.removeCallbacks(handleDelays);
} else {
pagerHandler.removeCallbacks(handleDelays);
pagerHandler.postDelayed(handleDelays, 1000);
}
} else {
if (pagerHandler != null) {
if (!isVisibleToUser) {
pagerHandler.removeCallbacks(handleDelays);
} else {
pagerHandler.removeCallbacks(handleDelays);
pagerHandler.postDelayed(handleDelays, 1000);
}
} else {
pagerHandler = new Handler();
}
}
}

AsyncTaskLoader onLoadFinished with a pending task and config change

I'm trying to use an AsyncTaskLoader to load data in the background to populate a detail view in response to a list item being chosen. I've gotten it mostly working but I'm still having one issue. If I choose a second item in the list and then rotate the device before the load for the first selected item has completed, then the onLoadFinished() call is reporting to the activity being stopped rather than the new activity. This works fine when choosing just a single item and then rotating.
Here is the code I'm using. Activity:
public final class DemoActivity extends Activity
implements NumberListFragment.RowTappedListener,
LoaderManager.LoaderCallbacks<String> {
private static final AtomicInteger activityCounter = new AtomicInteger(0);
private int myActivityId;
private ResultFragment resultFragment;
private Integer selectedNumber;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
myActivityId = activityCounter.incrementAndGet();
Log.d("DemoActivity", "onCreate for " + myActivityId);
setContentView(R.layout.demo);
resultFragment = (ResultFragment) getFragmentManager().findFragmentById(R.id.result_fragment);
getLoaderManager().initLoader(0, null, this);
}
#Override
protected void onDestroy() {
super.onDestroy();
Log.d("DemoActivity", "onDestroy for " + myActivityId);
}
#Override
public void onRowTapped(Integer number) {
selectedNumber = number;
resultFragment.setResultText("Fetching details for item " + number + "...");
getLoaderManager().restartLoader(0, null, this);
}
#Override
public Loader<String> onCreateLoader(int id, Bundle args) {
return new ResultLoader(this, selectedNumber);
}
#Override
public void onLoadFinished(Loader<String> loader, String data) {
Log.d("DemoActivity", "onLoadFinished reporting to activity " + myActivityId);
resultFragment.setResultText(data);
}
#Override
public void onLoaderReset(Loader<String> loader) {
}
static final class ResultLoader extends AsyncTaskLoader<String> {
private static final Random random = new Random();
private final Integer number;
private String result;
ResultLoader(Context context, Integer number) {
super(context);
this.number = number;
}
#Override
public String loadInBackground() {
// Simulate expensive Web call
try {
Thread.sleep(5000);
} catch (InterruptedException e) {
e.printStackTrace();
}
return "Item " + number + " - Price: $" + random.nextInt(500) + ".00, Number in stock: " + random.nextInt(10000);
}
#Override
public void deliverResult(String data) {
if (isReset()) {
// An async query came in while the loader is stopped
return;
}
result = data;
if (isStarted()) {
super.deliverResult(data);
}
}
#Override
protected void onStartLoading() {
if (result != null) {
deliverResult(result);
}
// Only do a load if we have a source to load from
if (number != null) {
forceLoad();
}
}
#Override
protected void onStopLoading() {
// Attempt to cancel the current load task if possible.
cancelLoad();
}
#Override
protected void onReset() {
super.onReset();
// Ensure the loader is stopped
onStopLoading();
result = null;
}
}
}
List fragment:
public final class NumberListFragment extends ListFragment {
interface RowTappedListener {
void onRowTapped(Integer number);
}
private RowTappedListener rowTappedListener;
#Override
public void onAttach(Activity activity) {
super.onAttach(activity);
rowTappedListener = (RowTappedListener) activity;
}
#Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
ArrayAdapter<Integer> adapter = new ArrayAdapter<Integer>(getActivity(),
R.layout.simple_list_item_1,
Arrays.asList(1, 2, 3, 4, 5, 6));
setListAdapter(adapter);
}
#Override
public void onListItemClick(ListView l, View v, int position, long id) {
ArrayAdapter<Integer> adapter = (ArrayAdapter<Integer>) getListAdapter();
rowTappedListener.onRowTapped(adapter.getItem(position));
}
}
Result fragment:
public final class ResultFragment extends Fragment {
private TextView resultLabel;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View root = inflater.inflate(R.layout.result_fragment, container, false);
resultLabel = (TextView) root.findViewById(R.id.result_label);
if (savedInstanceState != null) {
resultLabel.setText(savedInstanceState.getString("labelText", ""));
}
return root;
}
#Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
outState.putString("labelText", resultLabel.getText().toString());
}
void setResultText(String resultText) {
resultLabel.setText(resultText);
}
}
I've been able to get this working using plain AsyncTasks but I'm trying to learn more about Loaders since they handle the configuration changes automatically.
EDIT: I think I may have tracked down the issue by looking at the source for LoaderManager. When initLoader is called after the configuration change, the LoaderInfo object has its mCallbacks field updated with the new activity as the implementation of LoaderCallbacks, as I would expect.
public <D> Loader<D> initLoader(int id, Bundle args, LoaderManager.LoaderCallbacks<D> callback) {
if (mCreatingLoader) {
throw new IllegalStateException("Called while creating a loader");
}
LoaderInfo info = mLoaders.get(id);
if (DEBUG) Log.v(TAG, "initLoader in " + this + ": args=" + args);
if (info == null) {
// Loader doesn't already exist; create.
info = createAndInstallLoader(id, args, (LoaderManager.LoaderCallbacks<Object>)callback);
if (DEBUG) Log.v(TAG, " Created new loader " + info);
} else {
if (DEBUG) Log.v(TAG, " Re-using existing loader " + info);
info.mCallbacks = (LoaderManager.LoaderCallbacks<Object>)callback;
}
if (info.mHaveData && mStarted) {
// If the loader has already generated its data, report it now.
info.callOnLoadFinished(info.mLoader, info.mData);
}
return (Loader<D>)info.mLoader;
}
However, when there is a pending loader, the main LoaderInfo object also has an mPendingLoader field with a reference to a LoaderCallbacks as well, and this object is never updated with the new activity in the mCallbacks field. I would expect to see the code look like this instead:
// This line was already there
info.mCallbacks = (LoaderManager.LoaderCallbacks<Object>)callback;
// This line is not currently there
info.mPendingLoader.mCallbacks = (LoaderManager.LoaderCallbacks<Object>)callback;
It appears to be because of this that the pending loader calls onLoadFinished on the old activity instance. If I breakpoint in this method and make the call that I feel is missing using the debugger, everything works as I expect.
The new question is: Have I found a bug, or is this the expected behavior?

In most cases you should just ignore such reports if Activity is already destroyed.
public void onLoadFinished(Loader<String> loader, String data) {
Log.d("DemoActivity", "onLoadFinished reporting to activity " + myActivityId);
if (isDestroyed()) {
Log.i("DemoActivity", "Activity already destroyed, report ignored: " + data);
return;
}
resultFragment.setResultText(data);
}
Also you should insert checking isDestroyed() in any inner classes. Runnable - is the most used case.
For example:
// UI thread
final Handler handler = new Handler();
Executor someExecutorService = ... ;
someExecutorService.execute(new Runnable() {
public void run() {
// some heavy operations
...
// notification to UI thread
handler.post(new Runnable() {
// this runnable can link to 'dead' activity or any outer instance
if (isDestroyed()) {
return;
}
// we are alive
onSomeHeavyOperationFinished();
});
}
});
But in such cases the best way is to avoid passing strong reference on Activity to another thread (AsynkTask, Loader, Executor, etc).
The most reliable solution is here:
// BackgroundExecutor.java
public class BackgroundExecutor {
private static final Executor instance = Executors.newSingleThreadExecutor();
public static void execute(Runnable command) {
instance.execute(command);
}
}
// MyActivity.java
public class MyActivity extends Activity {
// Some callback method from any button you want
public void onSomeButtonClicked() {
// Show toast or progress bar if needed
// Start your heavy operation
BackgroundExecutor.execute(new SomeHeavyOperation(this));
}
public void onSomeHeavyOperationFinished() {
if (isDestroyed()) {
return;
}
// Hide progress bar, update UI
}
}
// SomeHeavyOperation.java
public class SomeHeavyOperation implements Runnable {
private final WeakReference<MyActivity> ref;
public SomeHeavyOperation(MyActivity owner) {
// Unlike inner class we do not store strong reference to Activity here
this.ref = new WeakReference<MyActivity>(owner);
}
public void run() {
// Perform your heavy operation
// ...
// Done!
// It's time to notify Activity
final MyActivity owner = ref.get();
// Already died reference
if (owner == null) return;
// Perform notification in UI thread
owner.runOnUiThread(new Runnable() {
public void run() {
owner.onSomeHeavyOperationFinished();
}
});
}
}

Maybe not best solution but ...
This code restart loader every time, which is bad but only work around that works - if you want to used loader.
Loader l = getLoaderManager().getLoader(MY_LOADER);
if (l != null) {
getLoaderManager().restartLoader(MY_LOADER, null, this);
} else {
getLoaderManager().initLoader(MY_LOADER, null, this);
}
BTW. I am using Cursorloader ...

A possible solution is to start the AsyncTask in a custom singleton object and access the onFinished() result from the singleton within your Activity. Every time you rotate your screen, go onPause() or onResume(), the latest result will be used/accessed. If you still don't have a result in your singleton object, you know it is still busy or that you can relaunch the task.
Another approach is to work with a service bus like Otto, or to work with a Service.

Ok I'm trying to understand this excuse me if I misunderstood anything, but you are losing references to something when the device rotates.
Taking a stab...
would adding
android:configChanges="orientation|keyboardHidden|screenSize"
in your manifest for that activity fix your error? or prevent onLoadFinished() from saying the activity stopped?