Develop Reference

Thread is started twice

I have a problem with my onCreate method. I have identified that when I switch to this activity the onCreate method gets called twice and therefore starting 2 threads which I dont want. Because the thread sends coordinates to a RaspberryPi and the 2nd unwanted thread always sends 0 0 0 which I dont want. I cant seem to find a fix for this so . . . I'd appreciate help if someone could tell me a fix so the thread starts only once.
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE);
Joystick = (ImageView) findViewById(R.id.Joystick);
Regler = (ImageView) findViewById(R.id.Regler);
buttonFoto = (Button) findViewById(R.id.buttonFoto);
buttonVideo = (Button) findViewById(R.id.buttonVideo);
buttonNeu = (Button) findViewById(R.id.buttonNeu);
buttonSpeichern = (Button) findViewById(R.id.buttonSpeichern);
touchscreenJoystick = (TextView) findViewById(R.id.touchscreenJoystick);
touchscreenJoystick.setOnTouchListener(this);
touchscreenRegler = (TextView) findViewById(R.id.touchscreenRegler);
touchscreenRegler.setOnTouchListener(this);
RL = (RelativeLayout) findViewById(R.id.activity_main);
running = true;
firstTouch = true;
Bild = (WebView) findViewById(R.id.webView);
Bild.loadUrl("http://10.0.0.1:8080/stream");
thread = new Thread(new MainActivity.TransmitThread());
thread.start();
}
EDIT:
I tried something with SaveInstanceState
//Same onCreate-stuff as above
if(savedInstanceState == null)
{
thread = new Thread(new MainActivity.TransmitThread());
thread.start();
}
}
#Override
protected void onSaveInstanceState(Bundle outState) {
outState.putString("message","crashed");
super.onSaveInstanceState(outState);
}
what this does is weird. Now I only have one thread that crashes immediately after sending the coordinates once.
Logs:
Log.i that i put before sending:
I/sent: //X: 0 //Y: 0 //Z: 0
Log that comes right after
I/System: core_booster, getBoosterConfig = false
Edit 2:
I've also tried starting the thread at an other timing. In my onTouch like this:
public boolean onTouch(View v, MotionEvent me)
{
xt = me.getX();
yt = me.getY();
int Aktion = me.getAction();
if(firstTouch)
{
thread = new Thread(new MainActivity.TransmitThread());
thread.start();
firstTouch = false;
}
//other stuff that i need to do here
}
But this results into the same as my try with SaveInstanceState a thread that transmits once but doesnt loop.
Edit 3:
I should probably post my thread too
class TransmitThread implements Runnable
{
#Override
public void run()
{
while(running)
{
delay();
xss = xs;
yss = ys;
zss = zs;
Log.i("sent","//X: " + xss + " //Y: " + yss + " //Z: " + zss);
transmit();
}
}
public void transmit()
{
try{
socket = new Socket(ServerIP,ServerPort);
OutputStream outputStream = socket.getOutputStream();
PrintStream printStream = new PrintStream(outputStream);
BufferedReader input = new BufferedReader(new InputStreamReader(socket.getInputStream()));
printStream.print(xs + " " + ys + " " + zs);
Akkustand = input.readLine();
handler.sendEmptyMessage(0);
}catch(UnknownHostException e){
e.printStackTrace();
}catch(IOException e){
e.printStackTrace();
}
}
public void delay(){
try {
Thread.sleep(200);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
FINAL EDIT:
I managed to do a workaround. I check before sending if the value is 0 if it is then I change it to 200. On the other end I check if its 200 and change it to 0 and ignore any 0 that I get.

First of all OnCreate will only be called one time for each lifetime of the Activity. However, there are a number of situations that can cause your activity to be killed and brought back to life. Thus, OnCreate get called again.
First thing you can debug the code and find the place where it called repeatedly.
Note: To avoid this situation you can save state information in onSaveInstanceState and restore it back in the state bundle you get in on create.
Thanks

OnCreate() already creates a main thread, and then you call another instance of the main class by manually creating a thread of the main class.

According to this answer all you dont need boolean check, just check if savedInstance is null, and only then start the second thread.
More general solution would be to initialise and start the thread in onStart() but dont forget to stop it in onStop() . If you want this thread to be long running in the background- I suggest start using something else- Service docs

Any configuration change will cause Android to restart your Activity like screen rotation, keyboard availability etc. what the system is actually doing is calling onDestroy() and then immediately calling onCreate(), meaning that the original Activity object is replaced by a new one without any knowledge of the executing background thread, so only the Activity object that started the thread knows that the thread was started.
A better way of handling this is through retaining thread in Activity.
The Activity class contains two methods for handling thread retention:
public Object onRetainNonConfigurationInstance()
called before configuration change occurs
public Object getLastNonConfigurationInstance()
Called in the new Activity object to retrieve the retained object returned in onRetainNonConfigurationInstance()
So you can implement this in following way.
private static MyThread t;
#Override
public void onCreate(Bundle savedInstanceState) {
Object retainedObject = getLastNonConfigurationInstance();
if (retainedObject != null) {
t = (MyThread) retainedObject;
}
else{
t = new MyThread();
t.start();
}
}
#Override
public Object onRetainNonConfigurationInstance() {
if (t != null && t.isAlive()) {
return t;
}
return null;
}

what is a good way to stop a thread in android

I am trying to passthrough the input obtained from the microphone to the speaker (the goal is to be able to perform audio processing in real time in the future). This is the code:
public class MainActivity extends Activity {
AudioManager am = null;
AudioRecord record =null;
AudioTrack track =null;
final int SAMPLE_FREQUENCY = 44100;
final int SIZE_OF_RECORD_ARRAY = 1024; // 1024 ORIGINAL
final int WAV_SAMPLE_MULTIPLICATION_FACTOR = 1;
int i= 0;
boolean isPlaying = true;
class MyThread extends Thread{
#Override
public void run(){
recordAndPlay();
}
}
MyThread newThread;
private void init() {
int min = AudioRecord.getMinBufferSize(SAMPLE_FREQUENCY, AudioFormat.CHANNEL_IN_MONO, AudioFormat.ENCODING_PCM_16BIT);
record = new AudioRecord(MediaRecorder.AudioSource.VOICE_COMMUNICATION, SAMPLE_FREQUENCY, AudioFormat.CHANNEL_IN_MONO,
AudioFormat.ENCODING_PCM_16BIT, min);
int maxJitter = AudioTrack.getMinBufferSize(SAMPLE_FREQUENCY, AudioFormat.CHANNEL_OUT_MONO, AudioFormat.ENCODING_PCM_16BIT);
track = new AudioTrack(AudioManager.MODE_IN_COMMUNICATION, SAMPLE_FREQUENCY, AudioFormat.CHANNEL_OUT_MONO,
AudioFormat.ENCODING_PCM_16BIT, maxJitter, AudioTrack.MODE_STREAM);
}
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
setVolumeControlStream(AudioManager.MODE_IN_COMMUNICATION);
init();
newThread = new MyThread();
newThread.start();
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
private void recordAndPlay() {
short[] lin = new short[SIZE_OF_RECORD_ARRAY];
int num = 0;
am = (AudioManager) this.getSystemService(Context.AUDIO_SERVICE);
am.setMode(AudioManager.MODE_IN_COMMUNICATION);
record.startRecording();
track.play();
while (true) {
num = record.read(lin, 0, SIZE_OF_RECORD_ARRAY);
for(i=0;i<lin.length;i++)
lin[i] *= WAV_SAMPLE_MULTIPLICATION_FACTOR;
track.write(lin, 0, num);
}
}
public void passStop(View view){
Button playBtn = (Button) findViewById(R.id.playBtn);
// /*
if(!isPlaying){
record.startRecording();
track.play();
isPlaying = true;
playBtn.setText("Pause");
}
else{
record.stop();
track.pause();
isPlaying=false;
playBtn.setText("Pass through");
}
// */
}
/*
#SuppressWarnings("deprecation")
#Override
public void onDestroy(){
newThread.stop();
}
*/
#Override
protected void onDestroy() {
android.os.Process.killProcess(android.os.Process.myPid());
// killProcess(android.os.Process.myPid());
}
}
Brief overview:
The while(true) {} infinite loop in recordAndPlay() function continuously reads raw audio samples from the microphone and outputs the raw samples to the speaker. recordAndPlay() is called from a Thread started in the onCreate() function. So it starts sending the input on the microphone to the speaker as soon as the program starts (well actually after a few seconds lag but I think this latency in unavoidable). I also have a button that can pause and resume this pass through. Now if the Thread is not stopped, the pass through continues even when I exit the application or the application looses focus (so even when the phone is on the desktop it keeps doing the passthrough).
#SuppressWarnings("deprecation")
#Override
public void onDestroy(){
newThread.stop();
}
This code causes the app to crash on exit (Why?) so I used
#Override
protected void onDestroy() {
android.os.Process.killProcess(android.os.Process.myPid());
// killProcess(android.os.Process.myPid());
}
that I found somewhere in stackoverflow (I forgot where). It seems to do what I want for now, but I want know if this is the proper way to stop the Thread or not. It does what I need, that is, it stops the passthrough when I exit the application, but I am not sure what exactly the killProcess() function does to my application overall, and if it is the best way to stop a Thread that I started myself.
Also, I can get the same effect if I exit my application (or loose focus to it) while the passthrough is being paused. But I assume this means the Thread is still running which means the infinite loop is also continuously running as well. Is it a good idea to do this, that is, just leave the Thread running, as long as my overall program is behaving as I want it to? What if I have lots of Threads or other background processes running? Can this practice cause memory problems in the future if the app grows too big?

Threads should periodically check for some shouldTerminate flag in their loop, then just set this flag from UI thread and (optionally) wait until thread terminate gracefully. Don't forget volatile or proper field synchronization.

Please remember to call super.onDestroy after releasing your memory or finishing the thread. Otherwise it will throw Exception:
#Override
protected void onDestroy() {
// You code here to finish the thread
super.onDestroy(); // Please call THIS too
}
Hope this helps.

Change your Thread class to something like this:
class MyThread extends Thread {
private volatile boolean finished = false;
#Override
public void run() {
while (!finished) {
// do stuff on thread
}
}
public void stopThread() {
finished = true;
}
}
In your onDestroy method call stopThread().
#Override
protected void onDestroy() {
newThread.stopThread();
super.onDestroy();
}
If you wish, you can also wait for thread to stop, by using this method:
private void joinThread(Thread thread) {
boolean retry = true;
while (retry) {
try {
thread.join();
retry = false;
} catch (InterruptedException e) {
// to be handled as you wish
}
}
}
Put this method in your activity and call it after newThread.stopThread().

There is already a provided flag for interuption.
Correct your while loop to the following.
And just call interupt(); in onDestroy or wherever.
private class thrd extends Thread {
#Override
public void run() {
super.run();
while (!isInterrupted()) {
//TODO
}
}
}
#Override
protected void onDestroy() {
super.onDestroy();
thrd.interupt();
}

Android Java - Message at a random range of time, every second check

For a side project of mine, I'm devoloping an android app with java. I don't know java a lot but i'm trying ^^.
The project is to have an Alarm at a random time in a certain range. The problem is that my chronometer and button freeze, but everything still works! Does anyone has maybe another solution for the thread.sleep ??
public class MainActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
public void StartChrono(View view) {
final Chronometer chrono = (Chronometer)findViewById(R.id.chronometer1);
chrono.setBase(SystemClock.elapsedRealtime());
chrono.start();
//Tick();
}
public int RandomTime(int min, int max)
{
int random = max - min;
Random rand= new Random();
random = rand.nextInt(random)+min;
return random;
}
public boolean CheckUp(int randomtime,int chronotime)
{
boolean check = false;
if(randomtime== chronotime)
{
check = true;
}
return check;
}
public void Tick()
{
boolean check = false;
int randomtime = RandomTime(20,150);
int time=1;
do
{
check = CheckUp(randomtime,time);
time = time +1;
try {
Thread.sleep(1000);
}
catch (InterruptedException e) {
AlertDialog alertDialog;
alertDialog = new AlertDialog.Builder(this).create();
alertDialog.setTitle("Error - 000");
alertDialog.setMessage("Could not check!");
alertDialog.show();
}
}while(check == false);
if(check == true)
{
AlertDialog alertDialog;
alertDialog = new AlertDialog.Builder(this).create();
alertDialog.setTitle("Yuy");
alertDialog.setMessage("Switch!");
alertDialog.show();
}
}
}

I wouldn't use Thread.sleep(), I would use a Timer.
You can set a time and the Timer automatically calls the associated task.
In Android it would work something like this:
http://android.okhelp.cz/timer-simple-timertask-java-android-example/
I used it once myself, but that is some time ago.
Btw.:
You don't have to write a method to check for a boolean value.
This also works:
boolean check = 5>3;
System.out.println("check: " + check);//"check true"

I'd definately use a Handler for this task: http://developer.android.com/reference/android/os/Handler.html
A basic example would be this:
long timeDelay = 1000; // Set this to your random number.
Handler handler = new Handler();
handler.postDelayed(new Runnable() {
#Override
public void run() {
// Do whatever you need to do after a specified interval.
}
}, timeDelay);
Instantiate the Handler inside your onCreate and keep the reference around so you can call it inside your method.
Just to clarify, why you can't use Thread.sleep() for "sleeping" a specific amount of time, is this: when you call Thread.sleep() you call it on the UI thread, so every component running on the UI thread (buttons, textfields and so on) will "sleep" for the given amount of time and hence you basically halt the whole application.
Also see the documentation for Thread.sleep:
Causes the thread which sent this message to sleep for the given
interval of time (given in milliseconds).

Android: Updating gridview multiple times after x seconds

I am having a problem updating the view in android every x seconds.
To get to know how android works I am writing a small game.
It has a GameController which holds the game loop. Inside the loop, the logic is executed and afterwards the gui will be informed about the changes.
The problem is that the changes cannot be seen in the view. The view stays the same until the game loop finishes and updates then only once.
Here is my code (the important parts):
GameController.java:
IGui gui;
public void play() {
while (playing) {
getAndProcessInput();
updateGui();
try {
Thread.sleep(500);
} catch (InterruptedException ex) {
}
}
}
private void updateGui() {
gui.setPlayer(x, y);
// ...
}
GameActivity.java:
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
GridView gridview = (GridView) findViewById(R.id.GridView1);
TextAdapter = new TextAdapter(this);
gridview.setAdapter(textAdapter);
GameController c = new GameController();
// here, the game loop shoud start.
// what i tried:
// new Thread(c).start(); <-- causes crash
// c.play(); <-- causes view to frease until game loop is done
this.runOnUiThread(c); <-- causes view to frease until game loop is done
}
TextAdapter.java:
public class TextAdapter extends BaseAdapter implements IGui {
private final Context context;
private final String[] texts;
public TextAdapter(Context context) {
this.context = context;
texts = new String[height * width];
for (int i = 0; i < texts.length; i++) {
texts[i] = " ";
}
}
public int getCount() {
return height * width;
}
public Object getItem(int position) {
return null;
}
public long getItemId(int position) {
return position;
}
public View getView(int position, View convertView, ViewGroup parent) {
TextView tv;
if (convertView == null) {
tv = new TextView(context);
tv.setLayoutParams(new GridView.LayoutParams(25, 25));
} else {
tv = (TextView) convertView;
}
tv.setText(texts[position]);
return tv; // <-- this happens only when game loop is done, not everytime something changed
}
#Override
public void setPlayer(int x, int y) {
texts[width * y + x] = "X";
// this.notifyDataSetChanged(); <-- this does not help (view still freases)
// gridview.invalidateViews(); does not help either
}
}
I googled a lot and tried a lot as well (and I do know that similar questions where asked here already, but they did not help me either), but somehow it just does not work.
I cannot get it do work that the view and logic run on different theads in android, and if they run on the same thread the logic blocks the view.
Any help would be greatly appreciated.
// edit:
If I try new Thread(c).start(); LogCat sais:
java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
And if I add Looper.prepare(); :
java.lang.RuntimeException: Unable to start activity ComponentInfo{GameActivity}: java.lang.RuntimeException: Only one Looper may be created per thread
If I try this.runOnUiThread(c); there are no errors.

First, this doesn't seems like the way to crate a game, you will need to use SurfaceView, or GLSurfaceView to better do what you want.
You can also look for Cocos2d for android, it's a 2D platform (that was ported from iPhone) that makes you life easier:
http://code.google.com/p/cocos2d-android/
I muse warn you though, I tried it a couple months back, and it was not production grade yet, it did crash from time to time.
Anyway, if you still want to continue heading your way I'll try answering your question:
I think you are messing too much with the way these stuff should work. try understanding first how handlers work with threads.
Do anything you want on your thread:
new Thread(new Runnable()
{
#Override
public void run()
{
try
{
calculateGameChangesHere();
handler.sendEmptyMessage(SUCCESS);
}
catch (Exception e)
{
handler.sendEmptyMessage(FAILURE);
}
}
}).start();
When your data is ready, tell the handler to put it in a view and show it:
protected Handler handler = new Handler()
{
#Override
public void handleMessage(Message msg)
{
if (msg.what == SUCCESS)
{
setCalculatedDataToaView(); // the data you calculated from your thread can now be shown in one of your views.
}
else if (msg.what == FAILURE)
{
errorHandlerHere();//could be your toasts or any other error handling...
}
}
};
This goes to everything that requires heavy processing/networking that shouldn't block your UI thread.
Hope this helps.

Not sure what you are trying to achieve by refreshing a listView every few seconds. Anyways if you are writing some 2d games, you have to use SurfaceView , which is especially meant for continuous refreshing.

Had the same problem and solved it using a pretty simple code.
Tips:
GridView must be refreshed by the UI thread
To display every change you must keep the loop and the Sleep method away from the UI thread
Solution:
Method to update the grid (put on your Activity that you build your GridView at the first place or wherever)
public void UpdateGrid(){
//your logic
//your way to change grid values (there are tones of other ways)
CustomGridAdapter cga = new CustomGridAdapter(this, values);
gridView.setAdapter(cga);
gridView.invalidateViews();
}
Build the non UI Thread that does the work
public class DataReceiver implements Runnable {
private MainActivity mainActivity;
public DataReceiver(MainActivity ma) {
mainActivity = ma;
}
#Override
public void run() {
for (int i = 0; i < 100; i++) {
mainActivity.runOnUiThread(new Runnable() {
public void run() {
//update the grid here
mainActivity.UpdateGrid();
}
});
//sleep here
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}

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