Android :: Callbacks Occur On Main (UI) Thread?
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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Aug 17, 2010
We are supposed to make UI actions only from the main UI thread. But it is not clear to me if callbacks like LocationUpdateListener (and other callbacks from sensors) are already in the UI thread or they require special care to access the UI components.
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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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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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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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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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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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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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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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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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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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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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Apr 26, 2012
I read somewhere that iPhone UI is so smooth because the thread which renders the UI has the REALTIME priority... so is that possible to mod android's UI thread priority?
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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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Jun 12, 2010
I wanna add three layout in a TabActivity, but it was force closed when I ran it.
Here is the code:
import android.app.TabActivity;
import android.content.res.Resources;
import android.os.Bundle;
import android.widget.TabHost;
public class Test1 extends TabActivity {
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Resources res = getResources();
TabHost tabHost = getTabHost();
tabHost.addTab(tabHost.newTabSpec("egcquery").setIndicator("EGCQuery").setContent(R.layout.main1));
tabHost.addTab(tabHost.newTabSpec("PatientInfo").setIndicator("PatientInfo").setContent(R.layout.main2));
tabHost.addTab(tabHost.newTabSpec("Comp_Interp").setIndicator("Comp_Interp").setContent(R.layout.main3));}
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Jun 3, 2010
I am having an interesting problem and would appreciate any advice. My app uses WebView as its primary view. Using a javascript hook, it can launch the camera so the user can take a picture. The camera is launched using: Intent i = new Intent(android.provider.MediaStore.ACTION_IMAGE_CAPTURE);
When the camera starts, it makes sense to use landscape mode, so the user naturally turns the phone on its side. After the user takes a picture, control returns to my launching Activity (actually, my Acitivity gets restarted because it usually gets destroyed to free up memory for the camera on my Moto Droid). When my WebView gets recreated, I restore its state from the Bundle I saved in onSaveInstanceState().
Now everything looks ok, except the phone is still in landscape mode. However, when the user turns the phone upright bringing back into portrait mode, my WebView takes up only half of the screen. Somewhere along the way, the scale of my WebView got lost. This seems like such a minor issue, but it is driving me crazy.
Does anyone have an idea why this might be happening? What is the correct way to preserve the scale of my WebView? I am hesitant to hard code any scale factors because what looks good on my device may not be the same for another.
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Apr 10, 2010
In my android app, I'm setting an alarm that I want to occur repeatedly, hence using AlarmManager.setRepeating().
I don't want to keep track of whether the alarm is set myself (sounds like a bad idea that's prone to fail at some point), and there seems to be no API support for checking whether a particular alarm is already set for a given Intent.
Hence, I am pessimistically resetting the alarm each time my app activates:
alarmManager.cancel(pendingIntent);
...
alarmManager.setRepeating(..., pendingIntent);
Question: is calling setRepeating() idempotent i.e. do I need to explicitly cancel() any prior alarm or can I safely just call setRepeating() and be done with it?
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Jan 9, 2010
After following some instructions on Diego Torres blog I am able to test my classes using the regular Eclipse JUnit test-runner, however I also want to be able to run my unit tests from within the emulated android environment. For now this should make no real difference since the classes I am working on do very basic numerical or networking tasks, but obviously anything which involves the UI or Android API specific functions can only ever be tested on the emulator.
I set up a new run configuration of type AndroidJUnitTest wich uses the ndroid.test.InstrumentationTestRunner, however whenever I fire up the test I get the following error in the console:
[2010-01-09 00:45:23 - Pal1]Uploading Pal1.apk onto device 'emulator-5556'....................
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Feb 25, 2010
Here I update my world to include the canvas size. world.getViewPort().updateViewPortSize(width,height); Is there a better way to do this? Is there a way that I can automatically update my world object without having to manually call it in the setSurfaceSize method but instead call it from My world class? My guess is that I can use some sort of callback, but I don't understand them!
/* Callback invoked when the surface dimensions change. */
public void setSurfaceSize(int width, int height) {
// synchronized to make sure these all change atomically
synchronized (mSurfaceHolder) {
mCanvasWidth = width;
mCanvasHeight = height;
world.getViewPort().updateViewPortSize(width,height); }
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Jul 2, 2009
I am using Android SDK 1.5. I am developing an activity with multiple content views. It will call setContentView() with different viewgroup instance for different functionality. It contains a text input dialog popped up by an option menu item. I didn't specify anything for IME in mainfest.xml & EditText attributes. I found at first, the soft keyboard for the text input dialog will overlap on the activity content view. But after several content view switch (by calling setContentView() with different ViewGroup instance), the soft keyboard will resize the activity content view. Why this inconsistent behavior happens?
...........................
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Oct 13, 2010
If it must implement with AIDL? And please kindly provide an example. There are several solutions, Does anyone know which is better?
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Sep 18, 2010
I have an android application. Based on the current geo location of user, I want to fetch some remote data in background and store it. My implementation is: At specific interval a alarm fires up my service. Service uses an anonymous class to query current location and registers a locationListener callback. On call of onLocationChanged() I initiate the remote data fetch from server.
However once my service is done registering the location listener using anonymos class, it returns as expected; as it doesn't wait for callback to happen before finishing. Since callback takes some time and makes a call when service has already returned, it throws an error saying: java.lang.RuntimeException: Handler{43e82510} sending message to a Handler on a dead thread
Which is quite understandable. One quick workaround for me now is that I can use getLastKnownLocation from locationManager as that doesn't respond back by callback; but what if I do want the latest location right now, in a service and not activity? How can I wait for callback to happen and stop my service from returning.
Also, at what point does lastKnownlocation gets updated? Everytime GPS registers a new location; does it update it? What I want to know is that if it's not latest can it still be closed to latest? As I didn't see an option in android emulator to configure the time period between subsequent updates.
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