Android :: Looper - Handler Issue
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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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 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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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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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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Feb 9, 2009
I need a message queue in my background thread, so I created a looper thread.
CODE:...................
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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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Aug 12, 2010
I am working on an application wich has its own URI prefix. (dchub:// in this case) is there a way when someone open his browser, clicks on a link starting with dchub:// my app starts using this address? so far found a lot of examples the otherway around opening the browser from your app but thats not what i'm looking for.
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Jul 20, 2010
I've got 2 classes GLLayer and GLCamTest. I'm attempting to run a method located in GLCamTest...
CODE:..........
I'm looking to run in on a thread from GLLayer but from what I understand I need a Handler..
CODE:.........
I'm starting the Thread from within public void onDrawFrame(GL10 gl) { my question is how would I implement said handler? I've read http://developer.android.com/reference/android/os/Handler.html but I still don't really understand how I'd implement it.
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Jun 29, 2010
I am very confused about handlers and looper can anyone plz explain it in simple terms to me any good links would be great.
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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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Aug 9, 2009
I've read the android AIDL documentation and have a general idea of how RPC works between an Activity and a Service. However, for my application it seems overboard to implement such features: basically, I want to pass a Service a nice handler so its thread can pass data to my Activity. Currently I'm getting around this by using a static public member (a hack) but I would prefer just passing a Handler object in the Service's starting Intent. However since a Handler isn't serialize-able , I haven't found a way to pass it to the service without a simple static member hack. Any insight? Or, am I just going to have to suck it up and do a formal RPC to the service?
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Sep 30, 2010
I am using a handler inside my service to display notifications at a certain time using the Handler.postDelayed method. My application runs fine on the emulator just as expected satisfying all cases. But when I installed the same on my HTC Wildfire, it simply doesn't happen as anticipated. Notifications are displayed at a random manner after the scheduled time and some notifications even fail. I'm monitoring my service from the Applications > Running Services and still my service is active.
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Nov 11, 2009
i want to do the following thing - when a user navigates to a web page, I want to have a link in there that looks like this: <p><a href="myprotocol://blah=42">Click here for fun.</a></p> Then when the user clicks on that from the phone browser, I want it to launch my intent with that full url. In my AndroidManifest.xml file, I have the following info: <activity android:name="com.test.MyActivity" style="@style/ MyStyle"> <!-- custom protocol association --><intent-filter><action android:name="android.intent.action.VIEW"></action> <category android:name="android.intent.category.DEFAULT"></category><category android:name="android.intent. category. BROWSABLE"> </category><data android:scheme="myprotocol"/></intent-filter></activity>When I try this, when I click on the link on the web page from the phone browser, it says -- Web page not available The Web page at myprotocol://blah=42 might be temporarily down or it may have moved permanently to a new web address.
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Nov 9, 2010
I'm trying to call a web server that is using relative URL redirects for some of the calls. This of course isn't working with DefaultHttpClient as it isn't treating it as a relative URL. I've gotten as far as implementing a RedirectHandler in an attempt to catch the redirect and add in the base call but I can't work out how to get the location of the redirect.
With the following method how do I go about finding out where I am being redirected to? I can't find any fields on either response or context that have what I need and I don't know where else to look.
public URI getLocationURI(HttpResponse response, HttpContext context)
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Jul 26, 2010
Assume that there activity A and B, A has a handler, now B is activate by A, how can i pass the handler to B? Currently i have a thread receive messages from socket, and dispatch messages to A and B, I think when B is activated, pass handler to B, then the handler can receive message from the thread. But I don't know how to do.
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Oct 30, 2010
I need to update my ui for an android app and I'm trying to use the Handler class to do it, using http://developer.android.com/resources/articles/timed-ui-updates.html and the android developer resources "Common Task" for using Handlers as guides.
Basically, I need something between the two - a timed update of the user interface, but without a button. So here is the relevent code that I am working on.
CODE:...............
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May 12, 2010
I will try to keep it simple:
In my main activity I make a handler:
CODE:.......
CODE:......
But if I call the handleMessage method from a callback function in a other Class, definitely from a other thread, I still get the exception message: CalledFromWrongThreadException (Only the original thread that created a view hierarchy can touch its views) :
CODE:...................
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Jul 1, 2009
I created a full-screen application and set the default orientation to landscape. When I open the keyboard the application crashes therefore I would like to override the method which executes on keyboard slide. Does anyone know which method is that?
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Jun 9, 2010
I need to download an image from the internet,in a different thread,and then send that image object in the handler message, to the UI thread.And by the way, is this the most efficient way to pass an object to the UI Thread?
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Oct 13, 2010
In Handler, we can pass some data from a background thread to the UI thread like this:
private void someBackgroundThreadOperation() {
final String data = "hello";
handler.post(new Runnable() {
public void run() {
Log.d(TAG, "Message from bg thread: " + data);
}
}
}
If we use the above, we cannot then use Handler.removeCallbacks(Runnable r), because we won't have references to any of the anonymous runnables we created above. We could create a single Runnable instance, and post that to the handler, but it won't allow us to pass any data through:.............
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Nov 20, 2010
I made a simple countdown timer and it works as expected when plugged in via usb for debugging but when I take it off debugging and the screen goes off either time out or power button the handler fails to fire at the end time. I have created a custom timer class that gets created from the main activity when needed, because its able to have multiple countdowns running at the same time. Am I right in thinking that the handler just gets paused when the screen goes off and if so what are my alternatives. The activity is still in the foreground and I assumed the handler would still fire if the screen goes off.
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Feb 2, 2010
My program threw a NullPointerException the other day when it tried to use a Handler created on another thread to send that thread a message. The Handler created by the other thread was not yet created, or not yet visible to the calling thread, despite the calling thread having already called start on the other thread. This only happens very rarely. Almost every test run does not get the exception. I was wondering what the best way is to avoid this problem for sure with minimal complication and performance penalty. The program is a game and very performance sensitive, especially once it is running. Therefore I try to avoid using synchronization after setup, for example, and would prefer to avoid spinning on a variable at any time.
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Apr 15, 2010
The first time issue it i give null as parameter to the function to the selection parameter is empty, meaning i don't filter any rows. The problem is i get only contacts i created myself using no syncAdapter. I used facebook app to synch my facebook contacts, but this query doesn't return them. I extracted the contacts.db from the emulator and the view_contacts view shows me all the contacts, so the DB is updated. What should i do to get all the contacts regardless of how they were created (with which synch adapter)
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Jul 9, 2009
I wish to analyze the various data passing through the browser. I would need a handler of the browser to query the contents. Is there any way that my application can get this handler of the browser and query for these data.
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Aug 13, 2010
I have to post messages from one process to another process by using handler .
I am using Handler.post/Handler.sendMessage but i am not getting those messages in another process. I am not getting any exceptions also.
Is it possible to sent messages across processes using Handler?
If it is the case how can i do it?
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