Use Looper.getMainLooper().getThread() to get the UI thread. You can check if it is the current thread using the following expression:

    Looper.getMainLooper().getThread() == Thread.currentThread()

It is UI thread if:

    Looper.myLooper() == Looper.getMainLooper()

Source AOSP source code: [`ManagedEGLContext.java#L100`][1], [`SharedPreferencesImpl.java#L470`][2], [`Instrumentation.java#L1650`][3] [and so on][4].


  [1]: https://github.com/android/platform_frameworks_base/blob/dbc51de44fe4f9a7f81528204250de32ec405d39/opengl/java/android/opengl/ManagedEGLContext.java#L100
  [2]: https://github.com/android/platform_frameworks_base/blob/dbc51de44fe4f9a7f81528204250de32ec405d39/core/java/android/app/SharedPreferencesImpl.java#L470
  [3]: https://github.com/android/platform_frameworks_base/blob/dbc51de44fe4f9a7f81528204250de32ec405d39/core/java/android/app/Instrumentation.java#L1650
  [4]: https://github.com/android/platform_frameworks_base/search?q=Looper.myLooper%28%29%20==%20Looper.getMainLooper%28%29&amp;ref=cmdform

Doesn&#39;t look like there is a method for that in the SDK. The check is in the [`ViewRoot`][1] class and is done by comparing `Thread.currentThread()` to a class member which is assigned in the constructor but never exposed.

If you really need this check you have several options to implement it:

 1. catch the android.view.ViewRoot$CalledFromWrongThreadException
 2. [`post`][2] a `Runnable` to a view and check `Thread.currentThread()`
 3. use a [`Handler`][3] to do the same

In general I think instead of *checking* whether you&#39;re on the correct thread, you should just *make sure* the code is always executed on the UI thread (using 2. or 3.).

  [1]: http://android.git.kernel.org/?p=platform/frameworks/base.git;a=blob;f=core/java/android/view/ViewRoot.java;h=bef3e580a0c5ad037a0b495979ecf567c5a80995;hb=HEAD#l2681
  [2]: http://developer.android.com/reference/android/view/View.html#post(java.lang.Runnable)
  [3]: http://developer.android.com/reference/android/os/Handler.html

If you want to know if you are in the main thread, you could maybe try:

    Context c = **Get a Context**;
    Thread.currentThread() == c.getMainLooper().getThread();

Of course, I could be wrong, and this could totally blow your app up.

I have spent the whole day trying to make my application use threads but with no luck. I have read much documentation about it and I still get lots of errors, so I hope you can help me.

I have one big time consuming method which calls the database and updates the GUI. This has to happen all the time(or about every 30 seconds).

    public class UpdateController
    {
        private UserController _userController;

        public UpdateController(LoginController loginController, UserController userController)
        {
            _userController = userController;
            loginController.LoginEvent += Update;
        }

        public void Update()
        {
            BackgroundWorker backgroundWorker = new BackgroundWorker();
            while(true)
            {
                backgroundWorker.DoWork += new DoWorkEventHandler(backgroundWorker_DoWork);
                backgroundWorker.RunWorkerAsync();
            }     
        }

        public void backgroundWorker_DoWork(object sender, DoWorkEventArgs e)
        {
            _userController.UpdateUsersOnMap();
        }
    }

With this approach I get an exception because the backgroundworker is not and STA thread(but from what I can understand this is what I should use). I have tried with a STA thread and that gave other errors.

I think the problem is because I try to update the GUI while doing the database call(in the background thread). I should only be doing the database call and then somehow it should switch back to the main thread. After the main thread has executed it should go back to the background thread and so on. But I can&#39;t see how to do that.

The application should update the GUI right after the database call. Firering events don&#39;t seem to work. The backgroundthread just enters them. 


**EDIT:**

Some really great answers :) This is the new code:

    public class UpdateController{
    private UserController _userController;
    private BackgroundWorker _backgroundWorker;

    public UpdateController(LoginController loginController, UserController userController)
    {
        _userController = userController;
        loginController.LoginEvent += Update;
        _backgroundWorker = new BackgroundWorker();
        _backgroundWorker.DoWork += backgroundWorker_DoWork;
        _backgroundWorker.RunWorkerCompleted += backgroundWorker_RunWorkerCompleted;
    }

    public void _backgroundWorker_ProgressChanged(object sender, ProgressChangedEventArgs e)
    {
        _userController.UpdateUsersOnMap();
    }

    public void Update()
    {   
        _backgroundWorker.RunWorkerAsync();
    }

    void backgroundWorker_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
    {
        //UI update
        System.Threading.Thread.Sleep(10000);
        Update();
    }

    public void backgroundWorker_DoWork(object sender, DoWorkEventArgs e)
    {
        // Big database task
    }
}


But how can I make this run every 10 second? System.Threading.Thread.Sleep(10000) will just make my GUI freeze and while(true) loop in Update() as suggested gives an exception(Thread too busy).

How to update GUI with backgroundworker?

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**Is there a way to have the latest JDK automatically when it&#39;s available?**

Of course, the update shouldn&#39;t get rid of old versions. That should be done manually since Eclipse is still using the old version. Once I&#39;ve updated my settings I would delete the old JDK manually.

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<p>How can I know if the running code is executed on the main thread (UI thread)?<br>
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http://docs.oracle.com/javase/1.5.0/docs/api/java/util/Timer.html

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My app shows a signup activity the first time the user runs the app, looks like:

 1. ActivitySplashScreen (welcome to game, sign up for an account?)
 2. ActivitySplashScreenSignUp (great, fill in this info)
 3. ActivityGameMain (main game screen)

so the activities launch each other in exactly that order, when the user clicks through a button on each screen.

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I think I can accomplish this with tasks (ie. start a new task on #3) but wanted to see if there was simpler method,

Thanks


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We are trying to use the native camera app to let the user take a new picture. It works just fine if we leave out the `EXTRA_OUTPUT extra` and returns the small Bitmap image. However, if we `putExtra(EXTRA_OUTPUT,...)` on the intent before starting it, everything works until you try to hit the &quot;Ok&quot; button in the camera app. The &quot;Ok&quot; button just does nothing. The camera app stays open and nothing locks up. We can cancel out of it, but the file never gets written. What exactly do we have to do to get `ACTION_IMAGE_CAPTURE` to write the picture taken to a file?

Edit: This is done via the `MediaStore.ACTION_IMAGE_CAPTURE` intent, just to be clear

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    &lt;property name=&quot;maxPoolSize&quot; value=&quot;1000&quot; /&gt;

What is the difference between the two and will it scale. Currently I have approx. 10000 users.

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I am having a real hard time finding a way to start, stop, and restart a thread in Java.

Specifically, I have a class `Task` (currently implements `Runnable`) in a file `Task.java`. My main application needs to be able to START this task on a thread, STOP (kill) the thread when it needs to, and sometimes KILL &amp; RESTART the thread...

My first attempt was with `ExecutorService` but I can&#39;t seem to find a way for it restart a task. When I use `.shutdownnow()` any future call to `.execute()` fails because the `ExecutorService` is &quot;shutdown&quot;...

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Content Type	Original Author	Original Content on Stackoverflow
Question	Arutha	View Question on Stackoverflow
Solution 1 - Android	Dan Syrstad	View Answer on Stackoverflow
Solution 2 - Android	balazsbalazs	View Answer on Stackoverflow
Solution 3 - Android	Josef Pfleger	View Answer on Stackoverflow
Solution 4 - Android	cesar	View Answer on Stackoverflow

How to check if running on UI thread in Android?

Android Problem Overview

Android Solutions

Solution 1 - Android

Solution 2 - Android

Solution 3 - Android

Solution 4 - Android

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Attributions