I understand that IntentServices allow running tasks on worker threads, however is the worker thread only spawn on call back to onHandleIntent?
Is the onCreate() called on the main thread and any object creation that takes place in the onCreate also takes place on the main thread?
Yes, onCreate() runs on the main thread.
If you print out the thread name in onCreate(), you get the following:
Thread[main,5,main]
However, you can spawn off background thread inside onCreate() if you don't want to block the main thread.
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I have a thread which is started in onCreate() and this thread fetches some data.
Is it possible that before the thread is terminated should be able to update the ListView?
Now as the thread is not the UI thread, it cannot directly update the listview array adapter.
Is there a way out?
I was thinking that is it possible to trigger a Handler from thread whose runnable gets executed on main UI thread.
Not sure if I understood your problem completely, but I believe there are two ways to achieve what you want:
1- Start an AsyncTask instead of a thread. AsyncTask's onPostExecute() will run in the UI thread, which means you can do anything UI-related in there. You can start the AsyncTask in onCreate(), and, once it finished, it calls a method on your activity which does:
myAdapter.notifyDataSetChanged();
2- Use runOnUIThread()
Use your Activity's runOnUiThread(Runnable action)
link
I read about this class:
Do not instantiate this class directly, instead, call
createSpeechRecognizer(Context). This class's methods must be invoked
only from the main application thread.
I suppose that the main application thread is the main Activity of an Android application...
Why should this class's methods be invoked only from the main application thread?
The main application thread is also known as the UI thread.
This is done to ensure thread safety. (No two processes can modify the same value at the same time).
Please see: Why can only the UI thread in Android update the UI?
If I want to implement a Handler object from within my Activity's main thread, do I need to call Looper.prepare() beforehand, or do activities already have their own internal loopers? Does the same hold true if I want to instantiate a Handler instance from within a Service?
The main thread already has its own looper. See Context.getMainLooper(). The main thread encompasses all Activities and Services in the application.
In Android, I have a thread that initializes a global variable. The thread starts when the activity starts. If the activity finishes before the thread initialized the global variable will the thread still run in the background to complete its job or it will be killed as the activity finishes?
The Activity finishing is part of the main execution/UI thread in android. When you spawn a new thread, and perform operations on that thread, it works as a separate entity from the main UI thread.
Hence, to answer your question - The thread will still run in the background to complete its job.
However, a word of caution. If within the run() method, you are using some objects that are part of the activity class that just got terminated, you can run into null pointer exceptions.
Can someone explain to me what exactly the UI thread is?
On developer.android.com it says about the runOnUiThread function
public final void runOnUiThread (Runnable action)
Since: API Level 1 Runs the specified action on the UI thread. If the
current thread is the UI thread, then the action is executed
immediately. If the current thread is not the UI thread, the action is
posted to the event queue of the UI thread.
Does the UI thread mean that this will be run everytime the activity is pushed the the background by some ui activity like incoming call or screen dimming etc.? If not, what exactly does the UI thread include ?
Thank you
The UIThread is the main thread of execution for your application. This is where most of your application code is run. All of your application components (Activities, Services, ContentProviders, BroadcastReceivers) are created in this thread, and any system calls to those components are performed in this thread.
For instance, let's say your application is a single Activity class. Then all of the lifecycle methods and most of your event handling code is run in this UIThread. These are methods like onCreate, onPause, onDestroy, onClick, etc. Additionally, this is where all of the updates to the UI are made. Anything that causes the UI to be updated or changed HAS to happen on the UI thread.
For more info on your application's Processes and Threads click here.
When you explicitly spawn a new thread to do work in the background, this code is not run on the UIThread. So what happens if this background thread needs to do something that changes the UI? This is what the runOnUiThread is for. Actually you're supposed to use a Handler (see the link below for more info on this). It provides these background threads the ability to execute code that can modify the UI. They do this by putting the UI-modifying code in a Runnable object and passing it to the runOnUiThread method.
For more info on spawning worker threads and updating the UI from them click here
I personally only use the runOnUiThread method in my Instrumentation Tests. Since the test code does not execute in the UIThread, you need to use this method to run code that modifies the UI. So, I use it to inject click and key events into my application. I can then check the state of the application to make sure the correct things happened.
For more info on testing and running code on the UIThread click here
If you execute blocking code (e.g. a Http-Request) in a separate Thread, consider using AsyncTask. Its doInBackground-Method runs on a separate Thread. AsyncTask provides you with methods onProgressUpdate and onPostExecute which are guaranteed to run on the UI thread.
If you need GUI-progress updates (e.g. via a progressbar) call publishProgress inside doInBackground. This leads to a subsequent call of onPublishProgress which is also guaranteed to run on the UI thread.
onPostExecute is automatically called after doInBackground returns.
All UI drawings etc. happen in a separate thread. Its called the UIThread. If you want to make any change to UI u must use make sure it happens in UIThread's context.
Easiest way of doing it is to make use of runOnUiThread