Develop Reference

How can you change ViewPager2 position inside the ViewPager2Adapter?

I programmed a Vocabulary Trainer with Vocabulary Cards. The Vocabulary Cards are Entries in a Room Database created from an asset. I am displaying these Vocabulary Cards with ViewPager2 in an Activity. I have a 'correct' and a 'false' button and when the user clicks on either, I want to update the Vocabulary Card (-> The entry in the sqlite database) and automatically swipe to the next item of the ViewPager2.
If I implement the buttons in the ViewPager2Adapter, I can't find a way to change the position of the ViewPager2. If I implement the buttons in the activity the sqlite entry does not update properly (After it updates the entry, the activity is constantly refreshed, it seems like it never the leaves the OnClick methode of the button).
So is it possible to change the position of ViewPager2 from inside the ViewPager2Adpater?
Thanks for your help!
That is the relevant code if I have the buttons in my ViewPager2Adapter. Here I don't know how to change the position of the ViewPager2
public void onBindViewHolder(#NonNull #NotNull ViewHolder holder, int position) {
VocabularyCard vocabularyCard = currentCards.get(position);
holder.btn_correct.setOnClickListener(view -> {
vocabularyViewModel.updateSingleVocabularyCard(vocabularyCard);
});
holder.btn_false.setOnClickListener(v15 -> {
vocabularyViewModel.updateSingleVocabularyCard(vocabularyCard);
});
That is the relevant code if I have the buttons in the Activity. Here the update function triggers an infinite updating of the Activity:
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_test);
initAll();
btn_correct_2.setOnClickListener(view -> {
int currentPos = viewpager2.getCurrentItem();
vocabularyViewModel.getCurrentCards().observe(this, vocabularyCards -> {
if (vocabularyCards.size() == currentPos){
Intent intent = new Intent(TestActivity.this, MainActivity.class);
startActivity(intent);
}else {
viewpager2.setCurrentItem(currentPos + 1);
}
VocabularyCard vocabularyCard = vocabularyCards.get(currentPos);
vocabularyViewModel.updateSingleVocabularyCard(vocabularyCard);
});
});
btn_false_2.setOnClickListener(view -> {
int currentPos = viewpager2.getCurrentItem();
vocabularyViewModel.getCurrentCards().observe(this, vocabularyCards -> {
if (vocabularyCards.size() == currentPos){
Intent intent = new Intent(TestActivity.this, MainActivity.class);
startActivity(intent);
}else {
viewpager2.setCurrentItem(currentPos + 1);
}
VocabularyCard vocabularyCard = vocabularyCards.get(currentPos);
vocabularyViewModel.updateSingleVocabularyCard(vocabularyCard);
});
});
Objects.requireNonNull(getSupportActionBar()).setTitle(getResources().getString(R.string.learn_new_words));
LiveData<List<VocabularyCard>> allNewCards = vocabularyViewModel.getAllNewCards(goal);
allNewCards.observe(this, vocabularyCards -> vocabularyViewModel.setCurrentCards(vocabularyCards));
vocabularyViewModel.getCurrentCards().observe(this, vocabularyCards -> {
viewPager2Adapter.setCurrentCards(vocabularyCards);
viewpager2.setAdapter(viewPager2Adapter);
viewpager2.registerOnPageChangeCallback(new ViewPager2.OnPageChangeCallback() {
#Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
super.onPageScrolled(position, positionOffset, positionOffsetPixels);
}
#Override
public void onPageSelected(int position) {
super.onPageSelected(position);
}
#Override
public void onPageScrollStateChanged(int state) {
super.onPageScrollStateChanged(state);
}
});
});
The update function in the Room DAO is straightforward:
#Update
void updateSingleVocabularyCard(VocabularyCard vocabularyCard);
I left out all the code that is not relevant.

There are several ways to propagate an event from the adapter to the activity where you manage your cards using ViewPager2. Let's have a look how it can be done either using an interface or using the same view model. But in any case I strongly recommend you to update your database in a background thread to prevent any possible UI lags.
1. Using an interface
This option is more flexible since you can propagate events as well as pass data as parameters. You can also reuse this interface for other cases. As far as I See you have a holder that has 2 buttons for the users to make choices. So our event here would be something like ChoiceEventListener, let's call this interface like so. Then you'd have to add a method to handle this event from within anywhere you wanna hear this event, and let's call its handle method onChoice(). Finally we would need a variable to indicate what the choice is. Now that ready to implement, let's write the new interface...
ChoiceEventListener.java
public interface ChoiceEventListener {
void onChoice(VocabularyCard vocabularyCard, boolean choice);
}
The next thing to do is to implement this interface where you want to listen to this event. In this case it is in your activity. There are 2 ways to do this:
You make your activity to inherit its methods using the implements keyword
YourActivity.java
public class YourActivity extends AppCompatActivity implements ChoiceEventListener {
// Use a background thread for database operations
private Executor executor = Executors.newSingleThreadExecutor();
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_test);
initAll();
// You must construct your adapter class with the listener
ViewPager2Adapter adapter = new ViewPager2Adapter(/* Other params... */, this);
}
#Override
public void onChoice(VocabularyCard vocabularyCard, boolean choice) {
if(choice) {
// User pressed the correct button
}
else {
// User pressed the false button
}
// Update card in the background
executor.execute(()-> vocabularyViewModel.updateSingleVocabularyCard(vocabularyCard));
}
}
You can implement it as an anonymous function
YourActivity.java
public class YourActivity extends AppCompatActivity {
// Use a background thread for database operations
private Executor executor = Executors.newSingleThreadExecutor();
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_test);
initAll();
// You must construct your adapter class with the listener
ViewPager2Adapter adapter = new ViewPager2Adapter(/* Other params... */, (vocabularyCard, choice) -> {
if(choice) {
// User pressed the correct button
}
else {
// User pressed the false button
}
// Update card in the background
executor.execute(()-> vocabularyViewModel.updateSingleVocabularyCard(vocabularyCard));
});
}
}
Finally the ViewPager2Adapter class implementation would be something like this:
ViewPager2Adapter.java
public class ViewPager2Adapter extends RecyclerView.Adapter<ViewPager2ViewHolder> {
// Here is your listener to deliver the choice event to it
private final ChoiceEventListener listener;
// Constructor
public ViewPager2Adapter(/* Other params... */, ChoiceEventListener listener) {
/* Other inits */
this.listener = listener;
}
public void onBindViewHolder(#NonNull #NotNull ViewHolder holder, int position) {
VocabularyCard vocabularyCard = currentCards.get(position);
holder.btn_correct.setOnClickListener(view -> {
listener.onChoice(vocabularyCard, true); // true for correct
});
holder.btn_false.setOnClickListener(v15 -> {
listener.onChoice(vocabularyCard, false); // false for false :)
});
}
}
2. Use the ViewModel for inter-communication
In this option we use a LiveData object to make page switching. The only thing you need to know in your activity is the current position which you get it from the adapter class. Once you update it in the adapter, set the current position value in live data so that you can switch the page in your activity.
VocabularyViewModel.java
public class VocabularyViewModel extends ViewModel {
public MutableLiveData<Integer> mldCurrentPosition = new MutableLiveData<>(0);
}
YourActivity.java
public class YourActivity extends AppCompatActivity {
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_test);
initAll();
vocabularyViewModel.mldCurrentPosition().observe(this, currentPosition -> {
if(currenPosition == null) return; // ignore when null
viewpager2.setCurrentItem(currentPosition + 1);
}
}
}
Finally the ViewPager2Adapter class implementation would be something like this:
ViewPager2Adapter.java
public class ViewPager2Adapter extends RecyclerView.Adapter<ViewPager2ViewHolder> {
// Use a background thread for database operations
private Executor executor = Executors.newSingleThreadExecutor();
public void onBindViewHolder(#NonNull #NotNull ViewHolder holder, int position) {
VocabularyCard vocabularyCard = currentCards.get(position);
holder.btn_correct.setOnClickListener(view -> {
// Update card in the background
executor.execute(()-> vocabularyViewModel.updateSingleVocabularyCard(vocabularyCard));
// Then invoke switching to the next card
vocabularyViewModel.mldCurrentPosition.setValue(position + 1);
});
holder.btn_false.setOnClickListener(v15 -> {
// Update card in the background
executor.execute(()-> vocabularyViewModel.updateSingleVocabularyCard(vocabularyCard));
// Then invoke switching to the next card
vocabularyViewModel.mldCurrentPosition.setValue(position + 1);
});
}
}

Dynamic UI Progress Updates using Interface + ExecutorService Issue

So I have a music application. I am trying to update the UI with the progress of the media player (like current time, current song, album cover) everytime the song changes. I found that using interfaces was a awesome magical way of communication between activity and fragments so I implemented an interface in my MusicManger class. My code will show what and how did it.
Two problems
1) Commented look below, ExecutorService seems to stop after one loop. No Errors in catch block (this is why I tagged with java)
2) Commented please look, All the System.out methods print but the UI doesn't update. I do believe I called the method from mainThread so it should update.
I'll show code in logical order will add titles in bold before code segment to tell you basic idea of code.
Passing UI references from fragment to MusicManager class, code below in Fragment class
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_item_songlist, container, false);
// Set the adapter
TextView musicManagerSongName, musicManagerCurrent, musicManagerTotal;
ProgressBar musicManagerProgress;
ImageView musicManagerImageView;
mListView = (AbsListView) view.findViewById(R.id.slist);
musicManagerSongName = (TextView)view.findViewById(R.id.textView12);
musicManagerCurrent = (TextView)view.findViewById(R.id.textView10);
musicManagerTotal = (TextView)view.findViewById(R.id.textView11);
musicManagerProgress = (ProgressBar)view.findViewById(R.id.progressBar);
musicManagerImageView = (ImageView)view.findViewById(R.id.imageView2);
MainActivity.mediaPlayer.passUIReferences(musicManagerSongName, musicManagerCurrent, musicManagerTotal, musicManagerProgress, musicManagerImageView, view);
// line above is a method within MusicManager that takes the references will show code next!
ImageButton playbutton = (ImageButton)view.findViewById(R.id.playbuttonbar);
ImageButton nextButton = (ImageButton)view.findViewById(R.id.nextbuttonbar);
ImageButton backButton = (ImageButton)view.findViewById(R.id.backbuttonbar);
ImageButton toggleButton = (ImageButton)view.findViewById(R.id.shufflebuttonbar);
ImageButton pausebutton = (ImageButton)view.findViewById(R.id.pausebuttonbar);
playbutton.setBackgroundResource(R.drawable.playbuttonbar);
playbutton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
try {
MainActivity.mediaPlayer.stateChange(1);
}catch(Exception e) {
}
}
});
backButton.setBackgroundResource(R.drawable.backbutton1);
nextButton.setBackgroundResource(R.drawable.nextbutton1);
toggleButton.setBackgroundResource(R.drawable.shufflebuttonselected);
pausebutton.setBackgroundResource(R.drawable.pausebutton1);
pausebutton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
try {
MainActivity.mediaPlayer.stateChange(0);
} catch (Exception e){
}
}
});
mListView.setAdapter(mAdapter);
((MainActivity) mListener).restoreActionBar();
return view;
}
As Commended above the code that is located in MusicManager class that takes references and stores them. Also shows interface implementation with MusicManager class. And the Executor service
public void passUIReferences(View... views) {
this.uiElements = views;
}
private ExecutorService executorService = Executors.newSingleThreadExecutor();
private MediaplayerUpdateInterface uiUpdateInterface;
public MediaPlayerManager(MediaplayerUpdateInterface inter) {
this.player = new MediaPlayer();
this.uiUpdateInterface = inter;
// The below line starts the single thread while loop for excutorservice and only loops and prints "this" once after I start one song then it never loops again
executorService.submit(new Runnable() {
#Override
public void run() {
while(true) {
if (player.isPlaying() && uiElements != null) {
System.out.println("this");
uiUpdateInterface.updateUI(uiElements, 0);
}
try {
Thread.sleep(500);
} catch (Exception e) {
e.printStackTrace();
}
}
}
});
}
public interface MediaplayerUpdateInterface {
public void updateUI(View[] views, int type);
}
Finally some code from MainActivity class that actually is suppose to update the UI note that both println's work as expected but only once as stated above because of the executorservice issue
public static MediaPlayerManager mediaPlayer = new MediaPlayerManager(new MediaPlayerManager.MediaplayerUpdateInterface() {
#Override
public void updateUI(View[] views, int type) {
System.out.println("check1 " + type);
updateMediaplayerViews(views, type);
}
});
private static void updateMediaplayerViews(View[] views, int type)
{
switch(type) {
case 0:
System.out.println("that?");
((TextView)views[0]).setText(mediaPlayer.getCurrentSongInfo().getName().length() > 22? mediaPlayer.getCurrentSongInfo().getName().substring(0, 19)+"..." : mediaPlayer.getCurrentSongInfo().getName());
break;
}
views[views.length - 1].invalidate();
}
The view array is shown perviously! Also the last view in the array is shown as the main view for songlist fragment.
I am sorry for all the code I've tried to debug it as you can see from my println's there is just something I am unaware of going on here.

Ok so there was an error that I needed to catch to see within the following code:
private static void updateMediaplayerViews(View[] views, int type)
{
switch(type) {
case 0:
System.out.println("that?");
((TextView)views[0]).setText(mediaPlayer.getCurrentSongInfo().getName().length() > 22? mediaPlayer.getCurrentSongInfo().getName().substring(0, 19)+"..." : mediaPlayer.getCurrentSongInfo().getName());
break;
}
views[views.length - 1].invalidate();
}
The issue is I was trying to change the view from a different thread then the one which created it. Solving it was pretty long and painful but basically I made it nonstactic used more interfaces then used the famous
Mainactivity.runOnUiThread(new Runnable(....));

Android communication between main thread and other thread

I want to change dynamically the text of a textview, but I will need the same logic if I want to make a game thread, so I need to make the communication between the main one and the second one.
I have the files :
MainActivity
public class MainActivity extends ActionBarActivity {
public static Handler mHandler;
Runnable thread = new SampleThread();
TextView txt1 = (TextView) findViewById(R.id.txt1);
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
ActionBar actionBar = getSupportActionBar();
actionBar.hide();
//hiding status bar
if (Build.VERSION.SDK_INT < 16) {
getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
WindowManager.LayoutParams.FLAG_FULLSCREEN);
} else {
View decorView = getWindow().getDecorView();
int uiOptions = View.SYSTEM_UI_FLAG_FULLSCREEN;
decorView.setSystemUiVisibility(uiOptions);
}
setContentView(R.layout.activity_main);
mHandler = new Handler() {
public void handleMessage(Message msg) {
// process incoming messages here
// i want to change the text of txt1 here
}
};
new Thread(thread).start();
}
}
SampleThread
package com.example.katsar0v.myapplication;
import android.util.Log;
/**
* Created by Katsar0v on 1/21/2015.
*/
public class SampleThread implements Runnable {
#Override
public void run() {
int two = 0;
while(two<10) {
two++;
try {
Thread.sleep(1000);
//instead of logging, i want to send the text to main UI
Log.d("MSG", String.valueOf(two + "sec"));
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
The problem I see is, how do I change the text with the handler, when my thread is in another file? Or should I make the second class static within the first one (and what should I do when the code gets really long, it can't be all in one file)?

You could implement a custom Interface in order to handle it from your main activity.
On your SampleThread:
public interface TextViewChangeListener
{
public void onTextViewChanged(String newName);
}
TextViewChangeListener mListener;
Then call mListener.onTextViewChanged(String newName) wherever you want to have the new name in your TextView. Remember to initialize mListener with an instance of your MainActivity first, otherwise you will get a null pointer exception. You can do that either in the constructor of SampleThread or by creating a method for the purpose.
In your activity you should implement SampleThread.TextViewChangeListener and override the onTextViewChanged.
#Override
public void onTextViewChanged(String newName)
{
//MyTextView.setText(newName);
}
Edit: untested code:
MainActivity:
public class MainActivity extends ActionBarActivity implements SampleThread.TextViewChangeListener {
#Override
public void onTextViewChanged(Message msg)
{
// process incoming messages here
// i want to change the text of txt1 here
}
public static Handler mHandler;
Runnable thread = new SampleThread(this);
TextView txt1 = (TextView) findViewById(R.id.txt1);
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
ActionBar actionBar = getSupportActionBar();
actionBar.hide();
//hiding status bar
if (Build.VERSION.SDK_INT < 16) {
getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
WindowManager.LayoutParams.FLAG_FULLSCREEN);
} else {
View decorView = getWindow().getDecorView();
int uiOptions = View.SYSTEM_UI_FLAG_FULLSCREEN;
decorView.setSystemUiVisibility(uiOptions);
}
setContentView(R.layout.activity_main);
new Thread(thread).start();
}
}
SampleThread:
package com.example.katsar0v.myapplication;
import android.util.Log;
/**
* Created by Katsar0v on 1/21/2015.
*/
public class SampleThread implements Runnable
{
public interface TextViewChangeListener
{
public void onTextViewChanged(Message msg);
}
public SampleThread(TextViewChangeListener mListener)
{
this.mListener = mListener;
}
TextViewChangeListener mListener;
#Override
public void run() {
int two = 0;
while(two<10) {
two++;
try {
Thread.sleep(1000);
mListener.onTextViewChanged(String.valueOf(two + "sec"));
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
Let me know if that helped.

You can find some examples in Grafika, which does a lot of work off the UI thread. For example, TextureFromCameraActivity has a pair of handlers, one for the UI thread, one for the renderer thread. In onResume() you can see the main thread passing its handler to the renderer through a constructor, then retrieving the renderer thread's handler with a method call.
ContinuousCaptureActivity has a slightly different approach, using a Handler that also implements a callback interface. The handler object is passed to the CircularEncoder constructor as an interface instance. The public callback methods use the Handler internally.
The only tricky bit is if you're passing a Handler out of the non-UI thread. You either need to do it before the thread starts, or use appropriate thread synchronization operations to avoid data races.
You don't need to have your classes in the same file (and you really shouldn't unless one is nested inside the other). If they're in the same package then the default (package) scope will let them see each other. The first example from Grafika uses nested / private classes, the second example is more spread out.
Of course, if all you're trying to do is submit UI events from a non-UI thread, you can just use Activity.runOnUiThread().

setContentView() inside of a thread

I'm making a simple Android game written in Java.
I have my activity...
public class GameName extends Activity{
...
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
}
Inside the "main" layout I have a button that calls a method called "startTheGame":
public void startTheGame(View v) {
theGame = new Panel(this);
setContentView(theGame);
}
Here is the panel code (simplified)
class Panel extends SurfaceView implements SurfaceHolder.Callback {
public GameThread _thread;
public Panel(Context context) {
super(context);
getHolder().addCallback(this);
setFocusable(true);
}
...
#Override
public void surfaceCreated(SurfaceHolder holder) {
_thread = new GameThread(getHolder(), this);
_thread.setRunning(true);
_thread.start();
}
...
}
So as you can see I have a "GameThread" class that is started... here it is below:
class GameThread extends Thread {
private SurfaceHolder _surfaceHolder;
private Panel _panel;
private boolean _run = false;
public GameThread(SurfaceHolder surfaceHolder, Panel panel) {
_surfaceHolder = surfaceHolder;
_panel = panel;
}
public void setRunning(boolean run) {
_run = run;
}
#Override
public void run() {
Canvas c;
while (_run) {
c = null;
try {
...
if (health <= 0) {
_run = false;
//change views?
setContentView(R.layout.over);
}
c = _surfaceHolder.lockCanvas(null);
synchronized (_surfaceHolder) {
_panel.onDraw(c);
}
...
} finally {
// do this in a finally so that if an exception is
// thrown
// during the above, we don't leave the Surface in an
// inconsistent state
if (c != null) {
_surfaceHolder.unlockCanvasAndPost(c);
}
try {
Thread.sleep(60);
} catch (Exception e) {
}
}
}
}
Hopefully you can see that if the health is <= 0 it stops the thread and I am trying to change to another layout I created called "over".
It just stops the screen from updating (drawing) but I never see the new panel.
I've tried:
GameName cs = ((GameName)getApplicationContext())
cs.setContentView(R.layout.over);
But I'm getting a ClassCastException...
Please Help!

You cannot cast your ApplicationContext to your main Activity (GameName) because this is not the same object. In a certain way, getApplicationContext() does not correspond to the first lauched Activity but to the app itself.
To me you should try to have distinct activities instead of trying to change the layout and the behaviour of a single Activity. It would be more simple for you and it would avoid the kind of issues you are facing.
Actually, each setContentView() I see in the code should correspond to a switch.
This way, you would have something like:
WelcomeActivity (probably GameName here): select the options of the game and start
PlayingActivity: the game itself. This is where the actual gameplay is.
GameOverActivity: displays the score, or anything you would like to show once the game ended
This without knowing which kind of game you are doing, but this skeleton should work well with arcade/action, roleplay/adventure or even maze/god-games.

I'd recommend looking into using Handlers. It allows you to safely communicate with the UI thread without worrying which thread you're currently on.

Why does my app force close when I setText in an update method?

I have an android app I am just experimenting things on and I cannot seem to figure out why my app force closes when I update a TextView via a while loop. When I comment out the updateText method it runs fine.
public class GameThread extends Thread {
Thread t;
private int i;
private boolean running;
private long sleepTime;
GameView gv;
public GameThread() {
t = new Thread(this);
t.start();
i = 0;
sleepTime = 1000;
}
public void initView(GameView v) {
this.gv = v;
}
public void setRunning(boolean b) {
this.running = b;
}
public boolean getRunning() {
return running;
}
public void run() {
while(running) {
i++;
update();
try {
t.sleep(sleepTime);
} catch(InterruptedException e) {
}
}
}
public void update() {
gv.setText(i); // when this is uncommented, it causes force close
Log.v("Semajhan", "i = " + i);
}
public class GameView extends LinearLayout {
public TextView tv;
public GameView(Context c) {
super(c);
this.setBackgroundColor(Color.WHITE);
tv = new TextView(c);
tv.setTextColor(Color.BLACK);
tv.setTextSize(20);
this.addView(tv);
}
public void setText(int i) {
tv.setText("i count: " + i);
}
public class Exp extends Activity {
GameThread t;
GameView v;
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
requestWindowFeature(Window.FEATURE_NO_TITLE);
getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
v = new GameView(this);
setContentView(v);
t = new GameThread();
t.setRunning(true);
t.initView(v);
}
public boolean onTouchEvent(MotionEvent event) {
if (event.getAction() == MotionEvent.ACTION_DOWN) {
if (t.getRunning() == true) {
t.setRunning(false);
Log.v("Semajhan", "STOPPED");
} else {
t.setRunning(true);
Log.v("Semajhan", "RESTART");
}
}
return true;
}
protected void onDestroy() {
Log.v("Semajhan", "DESTROYING");
super.onDestroy();
}
protected void onStop() {
Log.v("Semajhan", "Stopping");
super.onStop();
}
I though i'd post the whole app since it is relatively small and so that I could get some help without confusion.

First, when you get a Force Close dialog, use adb logcat, DDMS, or the DDMS perspective in Eclipse to examine LogCat and look at the stack trace associated with your crash.
In this case, your exception will be something to the effect of "Cannot modify the user interface from a non-UI thread". You are attempting to call setText() from a background thread, which is not supported.
Using a GameThread makes sense if you are using 2D/3D graphics. It is not an appropriate pattern for widget-based applications. There are many, many, many, many examples that demonstrate how to create widget-based applications without the use of a GameThread.

You have to call it from the UI thread.
For more info check: Painless Threading .
If you decide to use a Handler, the easiest solution for you will be to:
Extend a View, override it's onDraw , in it draw the game objects, after you have calculated the game data for them first of course
The Handler: (in your Activity)
private Handler playHandler = new Handler() {
public void handleMessage(Message msg) {
gameView.postInvalidate(); // gameView is the View that you extended
}
};
The game thread has a simple
Message.obtain(playHandler).sendToTarget();
In 2 words, the View is responsible for the drawing (you can move the calculations in a separate class, and call it before the onDraw), the thread is responsible only for scheduled calls to the Handler, and the Handler is responsible only to tell the View to redraw itself.

You cannot update the UI of your app outside of the UI Thread, which is the 'main' thread you start in. In onCreate(Context) of you app, you are creating the game thread object, which is what is doing the updating of your UI.
You should use a Handler:
http://developer.android.com/reference/android/os/Handler.html