Android :: Handler Fails To Deliver Message / Run Able To Main Thread
Feb 18, 2010
I have an app with a two threads - main and data loader. When data loader finishes it posts a Runnable object to the main thread (as described in the DevGuide), but it never gets delivered and run. Here's the basic code:
class MyApp extends Application{
public void onCreate()
{LoaderThread t = new LoaderThread();
t.start(); }
private class LoaderThread extends Thread {
public void run()
{ SystemClock.sleep(2000);
boolean res = m_handler.post(m_runnable);
if(res)
Log.d(TAG, "Posted Runnable"); } ............
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May 9, 2010
I try to make several connection in a class and update the multiple progressbar in the main screen. But I've got the following error trying to use thread in android : Code: 05-06 13:13:11.092: ERROR/ConnectionManager(22854): ERROR:Can't create handler inside thread that has not called Looper.prepare() Here is a small part of my code in the main Activity.
public class Act_Main extends ListActivity
{ private ConnectionManager cm;
public void onCreate(Bundle savedInstanceState)
{ super.onCreate(savedInstanceState);
// Set up the window layout
requestWindowFeature(Window.FEATURE_CUSTOM_TITLE);
setContentView(R.layout.main);
getWindow().setFeatureInt(Window.FEATURE_CUSTOM_TITLE, R.layout.custom_title); }
public void startConnection() { ......
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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 8, 2010
Since I got the original 2.2 update for my Droid, whenever I get a new text message and slide down the notification bar and select the new message, it takes me to the main text message window rather than the actual thread to reply to the person. It is really annoying because it requires an extra step. I figured it would be fixed with the second 2.2 update but it didn't. I called Verizon and they called Motorola and nobody knew of the problem so they shipped me out a new phone and it still does it! I am not sure if I am the only one experiencing this or if its normal. It doesn't do it 100% of the time but closer to 90% probably.
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May 21, 2009
I am writing an application in which i need to handle messages between the main thread(the deafult UI related thread) and the user created Gamethread.
The requirement is like this.
An activity(say "Activity_X") is setting the view by "setContentView(some "View_Y")". In "Activity_X" i have implemeted "onCreateOptionsMenu()" and "onOptionsItemSelected()" fucntions for creating menus & a switch case for action to be taken on selecting those menus.Menu has items like "resume/pause/zoom/" .
All action to be take on selecting these menus are implemented in "View_Y" in a separate Gamethread by extending "Thread" class.
So whenever a menu is selected in "Activity_X" i need to send a message to "View_Y". And on receiving this ,a particular action/method should be called in View_Y(GameThread).
How can i achieve this using Handlers?Is there any other way of doing this? Please do share with me some code snippets for these.
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May 27, 2010
I have a separate thread running to get data from the internet. After that, I would like to update the ListView in the main thread by calling adapter.notifyDataSetChanged(). But it does not work. Any workaround for that?
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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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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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Jul 16, 2010
The Android doc says "Like activities and the other components, services run in the main thread of the application process." Is the main thread here the same thing as UI thread?
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Mar 18, 2010
What is the difference when a class extend from Handler and Thread?
As described in developer.android.com
...
Each Handler instance is associated with a single thread and that thread's message queue.
...
Does the thread has no message queue ?
Any benefit for a class extend from Handler?
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Oct 15, 2009
I love the Hero - dont get me wrong - I am running the latest orange rom but I have a few issues- hopefully some one can help me solve...
1 - Dropped calls - no matter who or where I am calls drop about 25% of the time. I can be sitting at home doing nothing but talking then drop.. it happens alot.. starting to annoy me..
2 - Failed to send texts - I am having a text conversation then a random message stops and wont deliver - retry - retry again - wait a minute or 2 and retry - it works.... this is getting very anoying.. again about 25% of the time.
3 - Internet connection - (3g) - after about 4 or 5 clicks it will lock up and display page not found... wait about a minute - retry and again it works... this is about 40% of the time
4 - my friend sends me a text message/ missed call with a new number. I cant add it to an existing contact - it only allows you to add a new contact. plus copy and paste doesnt work at these points. - i end up having to write the number down and then edit the contact.
5- T9 - when I add a word to the library - it doesnt remember the word in my text - I have to type it in again and then it predicts it (minor but annoying). this phone is awsome as a gadget - but pretty crap as a phone. any one got any advice on how to help ?
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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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Jul 21, 2010
Are the UI threads for each Activity and Service in an app separate threads, or is there actually 1 underlying UI thread per app that processes the UI message queue for each Activity and Service?
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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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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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Feb 19, 2010
Can someone advise the am command (for adb shell) to run junit tests in the main thread please? The following shows onStart etc running in the test runner thread. am instrument -w -e class co.uk.telesense. tests.MyTest co.uk.telesense.tests/android.test.InstrumentationTestRunner Ewan Benfield ttp://www.telesense.co .uk tel: 0845 643 5691 (+44 845 643 5691) mob: +44 (0) 77859 26477
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Aug 20, 2009
I was define a new thread for a task, but when task is complete, I must to refresh my listview, however I will get the error for just can use main thread to change view,
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Oct 12, 2010
There are a lot of Android SDK APIs where callback handlers are registered. For a concrete example, with MediaPlayer you can set an onCompletionListener callback. Will these callbacks be called from the main (UI) thread? If the answer is "it depends", then I'm looking for some general rules for what callbacks will be called from the main thread versus another thread. The SDK documentation doesn't seem to spell it out. (Maybe I missed it) It seems important to know, because if I'm guaranteed main thread callbacks, then I can skip some thread synchronization on data shared between different places in code. If I'm forced to be pessimistic out of ignorance, then I have to write extra synch block code and worry about deadlocks, data integrity, and reduced performance.
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Jul 19, 2010
Say that a user clicks on a Button. Is the resulting onClick() function invoked on the main UI thread of the activity?
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Nov 16, 2010
I want to cancel a Toast to show the next one. This is the description of the behavious I want, when I select one element in the menu i display a toast from the actuel menu element, but if i switch from one element to an other quickly i'm creating a list of Toast to display. So i need to cancel the previous one but i never succed. This is an extract of my code: public class MainActivity extends TabActivity
private Toast toast; private String toastMsg;
private void toast(){ if(toast!=null){ toast.cancel(); } toast = Toast.makeText(MainActivity.this, toastMsg,Toast.LENGTH_SHORT);
toast.show(); } }
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Oct 19, 2010
Curious to know the reason behind not allowing updating UI elements from background thread in Android. Will main thread does something more (probably interacting with framework) after updating the UI elements so that changes can be seen on the screen? Is it the same case with other GUI tool kits?
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Feb 18, 2010
Hi, I've noticed that on android, the call to pthread_join does not suspend the calling thread. I've a number (6) of new thread created using pthread_create and pthread_join is called on each thread. But It does not suspend the main (calling) thread. I believe this relates to the port of pthread lib to android.
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Feb 7, 2014
I am trying to connect to a database, and I understand that it has to be outside of the main thread but i thought that this is what my code was doing...apparently not because i keep getting the error: android.os.NetworkOnMainThreadException.
package com.example.dbtesting;
import java.sql.*;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;
[code]....
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Jun 10, 2010
Are we guaranteed that Application.onCreate() runs in the UI/main thread? I want to assume so but I can't find any information to make me 100 % sure. When I receive a broadcast I want to post a message onto the UI/main thread. Currently I've added a function in my Application class to return a handler (created in it's onCreate), is this a good solution? If not, what would be a better solution?
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Mar 3, 2009
My purpose is very simple : each 1second, I want to redraw an object on different place on background. I do not know where my error on this code below. Here is my code:
public class My_View extends View{ private Bitmap mBackground_img;
private Drawable mMoveObject; private int mObjectw,mObjecth; private int Dx,Dy;
private Handler myHandler = new Handler(); private long lasttime;
public My_View(Context context,AttributeSet ats,int ds) {
super(context,ats,ds); init(context);
} public My_View(Context context,AttributeSet ats) { super(context,ats);
init(context); } public My_View(Context context) { super(context);
init(context); } public void change() { invalidate();
} private void init(Context context) {
Resources res = context.getResources();
mMoveObject = res.getDrawable (R.drawable.lander_firing);
mBackground_img = BitmapFactory.decodeResource(res, R.drawable.my_pic);
mObjectw = mMoveObject.getIntrinsicWidth();
mObjecth = mMoveObject.getIntrinsicHeight();
Dx = Dy = 0; lasttime = System.currentTimeMillis() + 1000;
Thread mthread = new Thread(null,doBackground,"Background");
mthread.start(); } private Runnable doBackground = new Runnable() {
public void run() { long now = System.currentTimeMillis();
if(lasttime < now ) { Dx = Dx + 10; Dy = Dy + 10;
lasttime = now + 1000; myHandler.post(change_view);
} } }; private Runnable change_view = new Runnable() {
public void run() { change();
} };
@Override public void onDraw(Canvas canvas) {
canvas.drawBitmap(mBackground_img,0 ,0 , null);
mMoveObject.setBounds(Dx, Dy, Dx+mObjectw, Dy+mObjecth);
mMoveObject.draw(canvas);
} }
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Feb 8, 2010
I am trying to start an error-reporting activty if unhandled exception detected. The problem is with exceptions thrown from main thread. Is there any way to start an activity if main thread crashed?
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Aug 13, 2010
In my game when the user completes a stage, I want the main game thread to pause/sleep/wait and a new activity to be launched called StageClear that displays information about points scored etc. After this has been displayed and the user has pressed continue I want the original game thread to resume where it left off. I have tried to implement this but have so far been unsuccessful, probably because I'm new to dealing with multiple threads and also the idea of synchronizing them. I most recently tried to implement a shared package-visible object that could notify after wait was called on itself, but I am getting errors in eclipse so it won't even compile, I think because though the object is declared public in an inner class, it cannot be seen or recognised by my activity elsewhere in a file in the package. I have already built both activities but my issue is getting the main game one to launch the other, and pause whilst it waits for this activity to finish, before the main game thread continues execution.
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Oct 7, 2010
connect / login are executed in the same thread of the caller, then are blocking - The packetlistener callbacks are called from smack receiver thread - The sendpacket enqueues the message to a queue. when I receive a message, I need to propagate it. I can use an handler, but it only gets the runnable object. How can I pass the data to the runnable called by the handler? I can't use a local variabile, because if I receive a lot of messages it will be overridden and I will loose some of them. Is it ok to use a queue to feed the runnable? Are there other techniques?
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Sep 6, 2010
I was curious about the nature of the handleMessage() and sendMessage() behavior of the Handler class. I want to be able to send message to another thread in such a way that the destination thread can process the message queue when it wants to. It seems, however, that the message is processed by handleMessage() practically as soon as it's sent.
I'm trying to design a game loop thread that does something like this:
CODE:.....
However, I as soon as sendMessage() is called (from the parent/calling thread), the Handler.handleMessage() is processed (in the child/receiving thread), even if the child/receiving thread is blocking in a while loop.
I've seen this problem solved in other games by using a thread-safe list (ConcurrentLinkedQueue). The UI thread just posts events to this queue, and the game loop can remove the events as it seems fit. I just assumed the Handler class was designed for this purpose. It seems it's more intended for asynchronous callbacks to the parent thread.
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May 22, 2010
How would I force the current thread to wait until another has finished before continuing. In my program the user selects a MODE from an AlertDialog, I want to halt executing of the program before continuing as the mode holds important configuration for the gameplay.
new AlertDialog.Builder(this)
.setItems(R.array.game_modes, new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
switch (which) {
case 0:
setMode(TRAINING_MODE);
case 1:
setMode(QUIZ_MODE);
default:
setMode(TRAINING_MODE);
break; ............
//continue loading the rest of onCreate();
contineOnCreate(); } })
.create().show();
If this is impossible can anyone give a possible solution?
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