Android :: Looper Inside An AsyncTask
Oct 27, 2009
I ran into some trouble trying to use a Looper inside an AsyncTask (its doInBackground method). Everything works fine until new Tasks are being created by AsyncTask.sThreadFactory, but once I reach the AsyncTask.CORE_POOL_SIZE limit and AsyncTask begins to recycle the threads, sending messages to my looper (created inside doInBackground) results in a MessageQueue RuntimeException: "sending message to a Handler on a dead thread".
The code I tried was:
CODE:....................
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Oct 6, 2010
What does the following exception mean? And how can I fix it?
This is the code:Toast toast = Toast.makeText(mContext, 'Somthing', Toast.LENGTH_SHORT);
This is the exception:
D/VVM ( 684): java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
D/VVM ( 684): at android.os.Handler.(Handler.java:121)
D/VVM ( 684): at android.widget.Toast.(Toast.java:68)
D/VVM ( 684): at android.widget.Toast.makeText(Toast.java:231)
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Sep 30, 2010
I am getting reports of 'Can't create handler inside thread that has not called Looper.prepare()' once I added ScoreNinja to my Android app, and released it to the market. It seems that it isn't happening all the time as the ScoreNinja highscore has lots of entries from users. I have looked on the web for help but there are no clear directions on what to do. I have used the ScoreNinja code exactly as shown on the scoreninja website. BTW If anyone is having problems with ScoreNinja only displaying one score, check to see if the launchmode is not set to 'singleinstance' in your manifest. This fixed it for me!
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Jun 23, 2009
Trying to get my head around the specific ins/outs of the Looper object and how it interacts with Threads. Documentation is rather scant on this topic. This is one of those topics that is obvious to the Android core team, but to the rest of us, it's not so obvious.
Can someone point to better documentation or give a more complete account of Looper:
1. What is looper.
2. How does the Android phone use Looper to coordinate message handling?
3. What do I need to do when I get the "Can't create handler inside thread that has not called Looper.prepare()" message?
4. How do I use LocationManager.requestLocationUpdates with Looper, and why does this call require a Looper object?
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Jul 28, 2010
I'm trying to figure out the correct way to create an AsyncTask to retrieve some data from the internet and then to take that data and bundle it up in an Intent and pass it to a new activity(A list display). So in the first activity I just have an EditText and Button. In the event of an OnClick the task should be called and when it is finished the data should be bundled inside an Intent and passed to the next Activity. The problem is when I take the results from onPostExecute and set them to an instance variable of the main activity, that instance variable is still null when the task is complete. Here is the barebones version of the code:
CODE:...........
When I debug the application I see onPostExecute does contain a valid PlacesList full of results, so why is the instance variable places set to null after the task is executed? I am going about "returning data" from an AsyncTask incorrectly?
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Aug 10, 2010
I have a doubt in Looper. I want to know when we should use Looper. If any good link for more clarification, it would be great.
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Jul 14, 2009
I have a thread that does all my rendering code for a game (including animations). I want to be able to communicate with that thread via Messages instead of locking / synchronization. This means that I need to both support a message queue and *also* support my own rendering loop. Normally I would just clear the message queue every frame of rendering so worst case scenario the messages sit on the queue for one frame before getting cleared out. This also gives a bit of priority to messages in that if the queue backs up the rendering will take a back seat until it empties out.
Everything was going fine until I realized that Looper doesn't have a "Clear the Queue" function! I looked at the source code for Looper.loop() and it appears that the code necessary to manually traverse the MessageQueue is protected, so I can't even write the ClearQueue function myself.
Does anyone here have any feedback on how I can have a thread that keeps the MessageQueue clear at the same time as allowing me to peg the CPU rendering as many frames per second as I can?
My current thought is to insert a message into the MessageQueue along the lines of "RenderOneFrame". When this message is popped off the queue I would render one game frame. Before returning from my rendering code though I would push another copy of the RenderOneFrame message back onto the queue. This means any messages added to the queue while I was busy rendering the frame would get processed before the RenderOneFrame mesage and once the queue was "clear" (ie: RenderOneFrame message was back on top) I would repeat the process.
I suspect that this will work, though I am open to suggestions for either a clear or faster method (I'm more interested in clean at this point, but at optimization time I'll be interested in faster if I bottleneck on this code).
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Sep 27, 2010
I'm trying to initialize OpenFeint in my game like this:
CODE:...........
Result: 1. OpenFeint initialization sometimes take so song(network actions?). It blocks the main thread. 2. My application remains in onCreate() for too long. 3. My Dev Phone One display ANR(application not responding) dialog prompting me to choose between 'Force Close' and 'Wait' 4. Soon after that, OpenFeint has done its things and my game shows up behind the dialog. 5. Now pressing 'Wait' will dismiss the ANR dialog and I can continue my game properly.
But obviously we don't want ANR dialog. So now I put it in a Thread like this:
CODE:...............
----------------------------------------------------------------------------- Result: Problem solved. Everything seems to run fine now.
I put Looper.prepare() there because my game will crash if I don't. The log message told me to put it there. I put Looper.loop(); there because OpenFeint will not initialize at all if I don't. I've read the doc about Looper but honestly I don't understand what the doc says.
Question 1. The doc also tell me this: ------------------------------------------------- public static final void loop ()
Since: API Level 1 Run the message queue in this thread. Be sure to call quit() to end the loop. -------------------------------------------------- Can anyone explain when & where should I call quit()?
Question 2 What will happen if I don't call Looper.quit()?
Question 3 Let me ask this straight. Am I taking the correct approach? Is there some kind of loop running alongside my game all the time if I do this?
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May 8, 2010
I have a thread I use to periodically update the data in my Activity. I create the thread and start a looper for using a handler with postDelay(). In onDestroy() for my activity, I call removeCallbacks() on my handler.
Should I then call handler.getLooper().quit()? Or not worry about it and let the OS deal with it? Or would it just run forever then, consuming CPU cycles?
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Oct 30, 2010
I've been a couple of days trying to solve this thing but I can'f figure it out.The problem is, simple activity, with simple layout, ScrollView -> LinearLayout -> and a lot of buttons inside the layout (within the scroll content). Everything works just fine but one tricky thing. When I click a button let's say at the top of the scroll content and inmediatelly I scroll down to the bottom of the content and I click other button there, nothing happens until I click a second time and all come to normal again.This can be reproduced anytime and it's code independent (i've tried more than 20 scenarios). I've not much experience in android yet but looks like the scroll listener stops the onclick listener or something like that.
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Feb 9, 2009
I need a message queue in my background thread, so I created a looper thread.
CODE:...................
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Oct 10, 2009
I'd like to know if Looper can enable handler to handle one message at a time, instead of handling all the messages in the queue together in one blocking call when Looper.loop() is called.
Because the looper sends all the messages in the queue to the handler one after the other in one blocking call, my application displays the ANR message. Instead, I want to be able to handle one single message, one blocking call at a time - the instant it falls into the queue.
The following code illustrates my problem: (pls note the lines referred: 1,2,3,4&5) Question 1: After calling looper.loop in line3, line4 and 5 don't run. Why is this? I tried quit(), but it doesn't help. Question 2: Instead of displaying 0,1,2,3,4 in one blocking call (at line3), I'd like to have 5 different blocking calls for each. Essentially (sorry, if i sound repetitive), I want to be able to use looper in such a way that each time, it ensures only one message gets handled.
Is there a way to do this?
CODE:..................
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Jul 7, 2009
So I've been extremely frustrated by this for a long time now.I've posted before, but can't seem to find a good solution. My goal is to have something pretty much exactly like the installed application details page in the Android Market.I need a list of items displayed along with other content above the list, and would like the content above to scroll up along with the list (exactly like the application details does for the "My Review" and other descriptive info).Due to responses to my previous posts, I came to believe that it really wasn't possible to do this with a ListView.So rather than using a ListView, I refactored my code to use a simple LinearLayout and add individual View items to the list, thinking I could just set each View as clickable and add an OnClickListener to each View in the LinearLayout.That's not working at all though, and now I'm getting even more frustrated.If someone can help me get the OnClickListener working, then I think it'll work, but I do need a separator for the LinearLayout.How do I add a separator like the one used for ListView to my LinearLayout?
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Sep 4, 2010
I am using an Executor [fixed thread pool] with my own ThreadFactory that adds a Looper:
CODE:...............
I am running a thread that makes network requests but if the network fails I would like a dialog message to be displayed to the user. This process is rather involving since it requires making AND displaying the request in the UI thread. I can wait for the user's response to the dialog by simply adding a Loop to the network thread and wait for a message to be send from the UI thread. This allows me to encapsulate the network requests in a while(tryAgain) thread. All works well except when the Looper.loop() method is called the second time (after a second network error dialog is displayed) and a message is sent by the dialog (in the UI thread) to the network thread's handler:
CODE:.............
In the AlertDialog instance is an OnClickListener:
CODE:...............
I've checked that the thread is still active with handler.getLooper().getThread().isAlive() which always returns true but it still gives me "sending message to a Handler on a dead thread". How is it that the Message/Handler has decided that the thread is dead? Shouldn't it rely on the .isAlive() method? In the end I am trying to avoid replicating the thread management build into the Android OS .
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Apr 6, 2010
I am working on a simple application (studying purposes) which list all the files from a selected folder. On top of that I would like to have a search feature where the user can search for files (the code for that is already in place). Now, I was thinking about having the search running in the background somehow, whilst the user can still navigate, create folders, copy, sort and do other stuffs normally. When the search finishes the user would get a notification and then could click on it and go to that activity (It ideally should be the same ListView I already use for browsing the files, I would just need to update the Adapter there with the latest processed data after clicking in the notification). What's the best answer for that? Threading or AsyncTask?
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Dec 27, 2009
Can anyone point me to a good example where a AsyncTask queries a local SQLite database and then updates the UI successfully. I have a database which I query using doInBackground... create a new custom SimpleCursorAdapter (overriding onViewBind), return the adapter (SimpleCursorAdapter), then in postExecute() create ListView adapter which is set to the the SimpleCursorAdapter, that was returned, then I set the listview adapter using SetAdapter(adapter);...
For some reason I throw an exception on fillWindow.java:200....
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Jul 15, 2009
My application parse an xml file dans display data in a list view. On start of application i load data using an AsyncTask. A Progress Dialog is display during the load. This part works fine.A button in the application make it possible to reload the data. I would like to run the AsyncTask but the sytem say i can't alter view in other thread. I have also read an AsyncTask can't be run another time So i would like to know what is the best way to do this and not to have the "application not responding" message.
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Aug 9, 2010
I know this is not how an async task should behave but my question is how to "block" the user while executing it.My need is the following: I have my own backup/restore process and I have an async task to run these two actions. The backup is fine, I can warn the user when the backup is done and that's just fine But my problem is about the restore process. When the user click on restore he shouldn't be able to make any change in the application (and anyway don't want to because he would lose all his changes).I understand that having the user blocked while restoring (or maybe with a progress bar) is not a best pratice but I do not see any other possibility in this context.
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Apr 9, 2010
I know how to use AsyncTask in a standard manner to manage operations that are in the background in relation to a UI thread.However,I want to run a task in the background which might run for a very long time under certain circumstances. In these cases, I would like to force the background task to fail if it runs for an excessive amount of time.I know that I can invoke the "get(long timeout, TimeUnit unit)" method of AsyncTask in my UI thread in order to terminate my background task if it runs too long. However, in that case, my UI will block while this "get()" command is waiting.There are probably other drawbacks to directly calling "get()" in this manner, not the least of which being an evil interaction with the "done()" method of AsyncTask's contained FutureTask object, which itself is calling "get()" at least this is what I see when I look at the source code for AsyncTask.
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Jul 5, 2010
I have an activity that needs to do some stuff in the background. When the background is done, I want it to load a new activity.I can successfully kick off the async task and using using ViewSwitcher I can show a nice progress dialog.However, when the user hit 'back' or 'close' from the new task, I want them to see the main screen of this task again. So, I use the showPrevious() after I start the new Activity, but I see the screen switch from the loading window back to the main window BEFORE the new Acitivity is launched.How do I get it to switch after the new activity, or when they come back from the new activity?I tried onRestart() and onResume() but both of them seem to give me a view of -1 that I couldn't do much with.
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Sep 20, 2010
I'm running a network service within an ASyncTask. I want to be able to time the task, and after a certain period of time interrupt it.Is there a simple way to do this? Basically, when the doInBackground() methods starts, I want to say "If it hasn't completed in 30 seconds, do something else".
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Jul 29, 2009
I'm developing a game based on SurfaceView and a game thread for the whole game thing.Now I want to do some HTTP requests triggered on events inside the thread. They should of course be asynchronous, so the game doesn't stop. I found AsyncTask to be a neat way to do this but I'm having trouble implementing this at the moment. Maybe I misunderstood the concept of AsyncTask,I don't know it just drives me nuts as I read docs and blogs and still I don't get it. So sorry if that's a dumb question but I'm mad of thinking about it.
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Mar 13, 2010
while debugging and app that uses AsyncTask to record audio and update UI I noticed that everytime that an AsyncTask object ends running (finishes doInBackground and onPostExecute or on Cancelled it´s thread stays alive (running status).At least for me that should not be the behavior of the class since the doInBackground task may not stay running forever (as an example the android manual says that a status bar should be updated by an asynctask, and it won´t last for the whole app running time).Is there anything I´m missing, as a method to destroy it, or should I just ignore and keep creating threads as I need and the VM will handle them as it needs resources?
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Jul 18, 2010
When I try to compile to following code, I get two errors:
Description Resource Path Location Type
Syntax error on token "void", invalid Expression AsyncTask.java /AsyncTask Project/src/org/me/asynctask line 19 Java Problem
Description Resource Path Location Type
The type AsyncTask is not generic; it cannot be parameterized with arguments AsyncTask.java /AsyncTask Project/src/org/me/asynctask line 25 Java Problem
CODE:............
Obviously AsyncTask IS a generic (http://developer.android.com/reference/android/os/AsyncTask.html#execute so why do i get those errors?
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Jan 7, 2010
In order to get XML data from a server repeatedly, I'm attempting to use AsyncTask and Timer as per Mark Murphy's suggestion. I get the following error:01-07 16:11:26.705: ERROR/AndroidRuntime(729): Caused by: java.lang.Runtime Exception: Can't create handler inside thread that has not called Looper.prepare()I'm using SDK 1.5 with Eclipse on Windows.I've looked in documentation, on StackOverflow and in the Android Developers group, but I'm not clear what's causing the error or how to fix it.I can get the data once - i.e. without Async and Timer - and parse it via SAX without problems.s: I'm quite new to Android.
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Apr 10, 2010
My program was going wonderfully. It is a search engine that connects to our back end database by sending Get requests to our server and displays the results. I've managed to get it to query my server and back end database, return results using JSON, return the first headers and pour them into a ListView widget in the main activity. Then when the user clicks on one of the headers it then sends another query from a sub-activity. It then parse those results and format them neatly into a WebView embedded into the sub-activity.
All this works perfectly. That is until I come to make a second query on the main activity. Listed below is my stack trace of where the error happens. I think I know why this is happening, but obviously not clearly understanding it.
I think it is because I am trying to call AsyncTask again. I remember reading that the AT can only be called once, but I presumed quite wrongly that this meant you can not do concurrent calls. I thought that once an AT had done it's task it was cleared and then could be called again, but this does not seem to be the case. Is it because of AT attempts at more than one call ? If so, would I be better changing that section into a Handler with a Runnable on the main activity?
-----Stack Trace----
CODE:.....................
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Dec 16, 2009
I'm working out my first multi-threaded application using Android with the AsyncTask class. I'm trying to use it to fire off a Geocoder in a second thread, then update the UI with onPostExecute, but I keep running into an issue with the proper Context.
I kind of hobbled my way through using Contexts on the main thread, but I'm not exactly sure what the Context is or how to use it on background threads, and I haven't found any good examples on it.
Here is an excerpt of what I'm trying to do:
CODE:...........
It keeps failing at the sixth line there, because of the improper Context.
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Feb 12, 2010
When using ThreadPoolExecutor can I use AsyncTask as the Runnable in my queue? Or does this defeat the purpose?
CODE:.....................
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Mar 5, 2010
Im using HTC Hero with HTS sense. Im experience that sometimes AsyncTask not will run doInBackground method on execute();
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Mar 26, 2010
I'm confused as to when one would choose AsyncTask over a Handler. Say I have some code I want to run every n seconds which will update the UI. Why would I choose one over the other?
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