Develop Reference

Android additional threads and Looper

I am writing a Android application which reads data from a SQLite Database and then displays the data on a next screen. Whenever I was doing a query on the database I would get an error message that too much work is being done on the main thread.
I then put my query in a new Thread:
(new Thread()
{
public void run()
{
Looper.prepare();
try
{
FPJobCardWizard data = dbHelperInstance.loadFPJobCardWizardFull(fitmentHash);
wState.fitmentItemSet(data.fitmentItemGet());
} catch (Exception e) {e.printStackTrace();}
Looper.loop();
}
}).start();
Now the gui/main thread is completing it's operation prior to the Query being complete and as a result the data variable is still empty. I read a few posts and the API documentation and it seems that I need to use a Looper (this seems to be the correct fix) but I have never used a Looper and cannot seem to get it to work.
Please can you check the code above and guide me in the right direction.
Thank you all in advance.

the best choice here will be using an AsyncTask, as it will enables you to perform all the background work in a background thread, then when the result is generated it will apply it using the UI thread:
So, as explained in the life cycle of AsyncTask, you can do all of your background work in the method doInBackground() and then do all of your UI work on the method onPostExecute() which will be executed after taking the result from doInBackground() method according to the life cycle, and to put your hands more on the AsyncTask, have a look at this example which provides the following example code:
public class AsyncTaskTestActivity extends Activity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
// This starts the AsyncTask
// Doesn't need to be in onCreate()
new MyTask().execute("my string paramater");
}
// Here is the AsyncTask class:
//
// AsyncTask<Params, Progress, Result>.
// Params – the type (Object/primitive) you pass to the AsyncTask from .execute()
// Progress – the type that gets passed to onProgressUpdate()
// Result – the type returns from doInBackground()
// Any of them can be String, Integer, Void, etc.
private class MyTask extends AsyncTask<String, Integer, String> {
// Runs in UI before background thread is called
#Override
protected void onPreExecute() {
super.onPreExecute();
// Do something like display a progress bar
}
// This is run in a background thread
#Override
protected String doInBackground(String... params) {
// get the string from params, which is an array
String myString = params[0];
// Do something that takes a long time, for example:
for (int i = 0; i <= 100; i++) {
// Do things
// Call this to update your progress
publishProgress(i);
}
return "this string is passed to onPostExecute";
}
// This is called from background thread but runs in UI
#Override
protected void onProgressUpdate(Integer... values) {
super.onProgressUpdate(values);
// Do things like update the progress bar
}
// This runs in UI when background thread finishes
#Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
// Do things like hide the progress bar or change a TextView
}
}
}

Connection pool has been closed in Sqlite Azure Mobile Service SDK

In my Android project i use Azure Mobile Services SDK and the way i make queries to the local sqlite database is like the following:
(example taken from http://azure.microsoft.com/en-us/documentation/articles/mobile-services-android-get-started-data/).
The problem is that i get the following errors:
1)com.microsoft.windowsazure.mobileservices.table.sync.localstore.MobileServiceLocalStoreException: java.lang.IllegalStateException: Cannot perform this operation because the connection pool has been closed
2) A SQLiteConnection object for database 'LocalDatabase' was leaked! Please fix your application to end transactions in progress properly and to close the database when it is no longer needed
3) java.util.concurrent.ExecutionException: com.microsoft.windowsazure.mobileservices.table.sync.localstore.MobileServiceLocalStoreException: java.lang.IllegalStateException: attempt to re-open an already-closed object
new AsyncTask<Void, Void, Void>() {
#Override
protected Void doInBackground(Void... params) {
try {
final MobileServiceList<ToDoItem> result = mToDoTable.where().field("complete").eq(false).execute().get();
runOnUiThread(new Runnable() {
#Override
public void run() {
mAdapter.clear();
for (ToDoItem item : result) {
mAdapter.add(item);
}
}
});
} catch (Exception exception) {
createAndShowDialog(exception, "Error");
}
return null;
}
}.execute();
In this implementation there is no Cursor or SQLiteOpenHelper object to close. What could i do?
Thank you!

I think this is because you are getting the result in one thread but trying to use that same result in the UI thread. One possible method is to use Broadcast or Eventbus to send the data back to the UI once the operation completes:
Here is sort of what I would do:
Futures.addCallback(mToDoTable.where().field("complete").eq(false).execute(), new FutureCallback() {
#Override
public void onSuccess(Object result) {
//Do something with result
//I would use event bus or broadcast here to notify the UI
}
#Override
public void onFailure(Throwable t) {
}
});
If this doesn't work, I would use the debugger and put a break point on that execute().get() line and see what is happening internally.
Here is another possible way to do it:
mToDoTable.where().field("complete").eq(false).execute(new TableQueryCallback<Object>() {
#Override
public void onCompleted(List result, int count, Exception exception, ServiceFilterResponse response) {
}
});

Android AsyncTask getting NetworkOnMainThreadException when called a second time

I'm getting some data off Parse.com in my app
When it first starts up, it checks the cache if available and displays it, then the user can pull-to-refresh to get the latest data
When the first refresh action is called, everything works great, but when I try to refresh a second time I get the NetworkOnMainThreadException force close
This is the calling method (I'm using Android support's swipe-to-refresh view)
#Override
public void onRefresh() {
// this part is merely a check, crashes both with or without this
if(!runningTask.getClass().equals(AsyncTask.Status.FINISHED))
runningTask.cancel(true);
runningTask = new DownloadEvents(true).execute();
}
This is the async task
private class DownloadEvents extends AsyncTask<Void, Void, ArrayList<Event>> {
boolean forceDownload;
String errorString = "";
public DownloadEvents(boolean forceDownload) {
this.forceDownload = forceDownload;
Parse.initialize(getActivity(), #API KEY CENSORED#);
}
// Do the long-running work in here
protected ArrayList<Event> doInBackground(Void... params) {
List<ParseObject> events = null;
PreferencesHelper ph = new PreferencesHelper(getActivity());
ParseQuery<ParseObject> eventsQuery = new ParseQuery<ParseObject>("events");
try {
eventsQuery.setCachePolicy(ParseQuery.CachePolicy.CACHE_ONLY);
events = eventsQuery.find();
} catch (ParseException e1) {
e1.printStackTrace();
}
if(forceDownload || System.currentTimeMillis() - ph.getLastEventsDownloadTime() > 43200000 || events == null)
{
swipeLayout.setRefreshing(true);
try {
eventsQuery.setCachePolicy(ParseQuery.CachePolicy.NETWORK_ELSE_CACHE);
events = eventsQuery.find();
ph.setLastEventsDownloadTime();
} catch (ParseException e) {
e.printStackTrace();
}
}
// creating classes and sorting goes here
return eventsList;
}
#Override
protected void onPreExecute() {
super.onPreExecute();
}
#Override
protected void onPostExecute(ArrayList<Event> events) {
if(events.size() > 0)
{
EventsAdapter adapter = new EventsAdapter(getActivity(), R.layout.events_card, events);
adapter.notifyDataSetChanged();
getListView().setAdapter(adapter);
}
if(errorString != "")
Toast.makeText(getActivity(), errorString, Toast.LENGTH_SHORT).show();
swipeLayout.setRefreshing(false);
}
}
Even if I force the download as the app start, it's always the second pulldown that crashes it, not the second time it downloads something
Please don't suggest turning off the NetworkOnMainThread strict rule, that's not a solution
Edit: here's the logcat
FATAL EXCEPTION: main
Process: com.mdk.test, PID: 24048
android.os.NetworkOnMainThreadException
at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1145)
at com.android.org.conscrypt.OpenSSLSocketImpl.shutdownAndFreeSslNative(OpenSSLSocketImpl.java:1102)
at com.android.org.conscrypt.OpenSSLSocketImpl.close(OpenSSLSocketImpl.java:1097)
at org.apache.http.impl.SocketHttpClientConnection.close(SocketHttpClientConnection.java:205)
at org.apache.http.impl.conn.DefaultClientConnection.close(DefaultClientConnection.java:161)
at org.apache.http.impl.conn.tsccm.AbstractConnPool.closeConnection(AbstractConnPool.java:320)
at org.apache.http.impl.conn.tsccm.ConnPoolByRoute.shutdown(ConnPoolByRoute.java:678)
at org.apache.http.impl.conn.tsccm.ThreadSafeClientConnManager.shutdown(ThreadSafeClientConnManager.java:256)
at com.parse.ParseRequest.initialize(ParseRequest.java:118)
at com.parse.Parse.initialize(Parse.java:109)
at com.mdk.test.EventsFragment$DownloadEvents.<init>(EventsFragment.java:136)
at com.mdk.test.EventsFragment.onRefresh(EventsFragment.java:223)
at android.support.v4.widget.SwipeRefreshLayout.startRefresh(SwipeRefreshLayout.java:441)
at android.support.v4.widget.SwipeRefreshLayout.onTouchEvent(SwipeRefreshLayout.java:399)
at android.view.View.dispatchTouchEvent(View.java:8073)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2253)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1987)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2259)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2001)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2259)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2001)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2259)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2001)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2259)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2001)
at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2259)
at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2001)
at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:2198)
at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1649)
at android.app.Activity.dispatchTouchEvent(Activity.java:2717)
at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:2159)
at android.view.View.dispatchPointerEvent(View.java:8263)
at android.view.ViewRootImpl$ViewPostImeInputStage.processPointerEvent(ViewRootImpl.java:4013)
at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:3892)
at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3454)
at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3507)
at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3473)
at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:3583)
at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3481)
at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:3640)
at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3454)
at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3507)
at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3473)
at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3481)
at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3454)
at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:5682)
at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:5656)
at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:5627)
at android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent(ViewRootImpl.java:5761)
at android.view.InputEventReceiver.dispatchInputEvent(InputEventReceiver.java:185)
at android.view.InputEv

Parse.initialize() is in the async task constructor that gets executed in the main thread and it invokes a network operation.
Move the call to doInBackground().

It's hard to tell exactly where the problem occurs, because you didn't post the stacktrace, but this line looks suspicious:
swipeLayout.setRefreshing(true);
You can't modify any views on your doInBackground, and it looks like this might be doing just that.
Another fishy line is:
PreferencesHelper ph = new PreferencesHelper(getActivity());
Apparantly this object needs the activity, which may or may not cause a NetworkOnMainThread exception later on. You can't touch the UI in your doInBackGround method.
Just keep the doInBackground clean and only do the network stuff there, don't entangle it with other things.

event.size()
For null data will throw an exception error, however not sure if that is the exact issue you are facing.

How to work with AsyncTask and threads?

The goal:
Using Google App Engine server and Android client, I'm trying to put on the Google map at the Android client Users overlays. Every 30 seconds I'm polling the server and getting Vector that contains users and adding it to the map.
Current status:
I'm dong all that using in one new thread, So after running the app I got:
weird behaviors(delayed overlays, multiple overlays) and after that crushed with ConcurrentModificationException.
After reading a bit i figured out that I need to work with AsyncTask.
Correct me if I'm wrong,But I understand that everything done in the Activity at at onCreate is "running" in UIhread so I need to put the "Logic" (All the Network handling) in doInBackground and all the UI Handling like putting overlays on the map in onPostExecute.
My Question are:
1) In the current status I'm doing:
new Thread()
{
#Override
public void run()
{
super.run();
while(true)
{
SystemClock.sleep(30000);
Vector responseFromServer = getUsersVectorFromServer();
putNewOnlineUserOnTheMap();
}
}
}.start();
What is the right way to convert this To AsyncTask?
Do I poll the server still using new thread in the doInBackground or there is right way to do this?
2) Is there a specific list of what counts as UI to put in onPostExecute or any concepts list?
In my case I guess that in need to put putNewOnlineUserOnTheMap() in onPostExecute.
Thanks.

Something similar to the following:
class UpdateTask extends AsyncTask<Void, Vector, Void>{
#Override
protected Void doInBackground(Void... params) {
// this is running in a background thread.
while (!isCancelled()) {
SystemClock.sleep(30000);
Vector responseFromServer = getUsersVectorFromServer();
// send the result back to the UI thread
// onProgressUpdate will be called then
publishProgress(responseFromServer);
}
return null;
}
#Override
protected void onProgressUpdate(Vector... values) {
// this is executed on the UI thread where we can safely touch UI stuff
putNewOnlineUserOnTheMap(values[0]);
}
}
You can't use the result of the task since the task is finished then. But you can use the progress publishing mechanism to get periodic results. If you use it like that and do the modification on the UI thread you should not get ConcurrentModificationException because you do the modifications on the one thread that can safely modify the UI.
One thing to note here: create new instances of your Vector in the background thread and then use it to update the UI. But don't touch the same object afterwards in the backgroundthread. That way you don't need any synchronization since after the background thread sends it away it is only the UI thread that touches it. (and you could use a simple ArrayList instead of a Vector)

AsyncTask uses generics and varargs.The parameters that are passed to the asyntask are . TypeOfVariableArgumentsParameters is passed into the doInBackground(), ProgressParam is used for progress information and ResultParam must be returned from doInBackground() and is passed to onPostExecute() as parameter.
example:--
protected class ParsingTask extends AsyncTask> {
private ProgressDialog loadingDialog = new ProgressDialog(JsonParserActivity.this);
protected void onPreExecute() {
loadingDialog.setMessage("loading app store..");
loadingDialog.show();
}
#Override
protected ArrayList<Items> doInBackground( Context... params ) {
// do ur process here.
return result;
}
if (!this.isCancelled()) {
}
return result;
}
#Override
protected void onProgressUpdate(String... s) {
super.onProgressUpdate(s);
Toast.makeText(getApplicationContext(), s[0], Toast.LENGTH_SHORT).show();
}
#Override
protected void onPostExecute( ArrayList<Items> response ) {
//if u r dealing with list view and adapters set the adapter here at the onPostExecute()
loadingDialog.dismiss();
}
#Override
protected void onCancelled() {
super.onCancelled();
Toast.makeText(getApplicationContext(), "The operation was cancelled", 1).show();
}
}

You can use AsyncTask like below. Hope this will help you..
Class YourClass{
void YourClass(){
NetworkTask nT = new NetworkTasK();
nT.execute();
}
}
protected class NetworkTask extends AsyncTask<Void, String, Boolean>
{
#Override
protected Boolean doInBackground(Void... params)
{
try
{
String response;
while(keepreceiving)
{
response = in.readLine();//Prog Counter stops here until getting i/p.
if(response != null)
yourFunctionForResponse(response);
}
}
catch (Exception ex)
{
}
return null;
}
private void yourFunctionForResponse(String response){
//things to do....
}
}
You may also try runOnUiThread(Runnable action) along with this to implement your work.

How to run queries in the background

I have listed of products with different category. I have to sort them. Because of the queries, It is taking more time to load. Between two activities, the screen is coming black. I want to run the query in the background. How can I do that and how to use its result in main activity?
private class InsertTask extends AsyncTask {
String cat;
#Override
protected void onPreExecute() {
super.onPreExecute();
}
#Override
protected Boolean doInBackground(String... params) {
Boolean success = false;
try {
category(cat);
success = true;
} catch (Exception e) {
if(e.getMessage()!=null)
e.printStackTrace();
}
return success;
}
#Override
protected void onPostExecute(Boolean success) {
super.onPostExecute(success);
}
private void category(String category) {
try{
Cursor1 = mDbHelper.fetchcategory(category);
}catch(Exception e){
Log.v("Excep", ""+e);
}
}
And when called
InsertTask task = new InsertTask();
task.execute();
I have listed the category in buttons. How can I get the values then?

You should use AsyncTask for that. And some more info.

Its good you have thought of AsyncTask. Firstly, you can declare this class as inner in you class activity (if you haven't previously did) and so you are able to access you view class members.
You can do this also by creating thread and one handler that will be used to update your UI components. Remember that if you use threads you'll need to lock/unlock your database object because of the thread safety(if any other thread is accessing the database for any reason). Read more about thread safety of dbs.

I was doing some searching myself, and I came across this read, its rather long but looks extremely helpful, with lots of code examples. (I bookmarked it for myself).
Threads, Async, and Handlers O MY!
But some form of threading is the ticket.
From Android dev.
(My favorite code snippet)
public void onClick(View v) {
new Thread(new Runnable() {
public void run() {
//Do Work here
}
}).start();
}