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Using timers - how to?

I got a problem with timer. After 2 sec instead of this action I am getting an error.
public class MainActivity extends AppCompatActivity {
private TextView tv;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
tv = (TextView)findViewById(R.id.tv);
Timer timer=new Timer();
TimerTask timerTask = new TimerTask() {
#Override
public void run() {
tv.setText("why?");
}
};
timer.schedule(timerTask,2000);
}
}
How to fix this?

You cannot run these from non main thread
#Override
public void run() {
tv.setText("why?");
}
You have to use runOnUiThread
#Override
public void run() {
runOnUiThread(new Runnable(){
#Override
public void run() {
tv.setText("why?");
}});
}
}
Or use post method of View like
#Override
public void run() {
tv.post(new Runnable(){
#Override
public void run() {
tv.setText("why?");
}});
}
}
I know it looks like weird, but if you write it using lambdas its much better and concise
timer.schedule(()->{tv.post(()->{setText("why?");}},2000);

You cannot update UI from inside a thread. Update UI from main thread.
Create a handler and send message to the handler after your work has been completed and update the UIthere.
Handler handler = new Handler()
{
#Override
public void handleMessage(Message msg) {
super.handleMessage(msg);
// Update UI
}
};
and send message to handler using handler.sendMessage()

CountdownTimer crashing app. Trying to update UI thread on tick

I want the countdowntimer to be on a separate thread and for it to update the UI on each tick. Every time I click start the app just closes and I get the 'app has stopped' error message.
public class Activity_MultiplayerGame extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity__multiplayer_game);
}
public void btnStart_onClick(View view){
CountDownTimer timer = new CountDownTimer(15000, 1000){
#Override
public void onTick(final long millisUntilFinished) {
runOnUiThread(new Runnable() {
#Override
public void run() {
TextView countdownText = (TextView) findViewById(R.id.countdown);
Integer timeUntilFinished = (int) millisUntilFinished/1000;
countdownText.setText(timeUntilFinished);
}
});
}
#Override
public void onFinish() {
TextView countdownText = (TextView) findViewById(R.id.countdown);
countdownText.setText("Finished");
}
};
timer.start();
}
}
I've made the assumption that creating a CountDownTimer gives it its own thread?

you can use Handler. I wrote a sample for you
this code increase a counter every one second and show and update counter value on a textView.
public class MainActivity extends Activity {
private Handler handler = new Handler();
private TextView textView;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
textView = (TextView) findViewById(R.id.text);
startTimer();
}
int i = 0;
Runnable runnable = new Runnable() {
#Override
public void run() {
i++;
textView.setText("counter:" + i);
startTimer();
}
};
public void startTimer() {
handler.postDelayed(runnable, 1000);
}
public void cancelTimer() {
handler.removeCallbacks(runnable);
}
#Override
protected void onStop() {
super.onStop();
cancelTimer();
}
}

You cannot update UI from other thread than main (ui) thread on android. There are many ways to approach the problem, but I suppose you should start with AsyncTask if you really need another thread. Check doInBackround and onProgressUpdate methods.
If you don't need other thread (and if this is only about the counter you dont') you can check Handler class and postAtTime(Runnable, long), postDelayed(Runnable, long) methods. Or you can make subclass of Handler class and use combination of sendMessageDelayed(android.os.Message, long) and overridden handleMessage().

Here's your problem:
countdownText.setText(timeUntilFinished);
You have passed integer to setText(int) method, which actually takes the string resource id rather than the integer to be displayed. You should use the method setText(String).
Try this:
countdownText.setText(String.valueOf(timeUntilFinished));

This code also work it decrease counter(or increase whatever you want) and show in text view you can also stop or reset counter via click the same button.
public class MainActivity extends AppCompatActivity {
TextView textView;
Button count;
boolean timelapseRunning = true;
int NUM_OF_COUNT=15;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
textView=(TextView)findViewById(R.id.textview);
count=(Button)findViewById(R.id.count);
runTimer();
}
public void onclick(View view){
if (!timelapseRunning) {
timelapseRunning=true;
} else {
timelapseRunning = false;
}
if(NUM_OF_COUNT==0){
NUM_OF_COUNT=15;
}
}
private void runTimer() {
final Handler handler = new Handler();
handler.post(new Runnable() {
#Override
public void run() {
textView.setText(""+NUM_OF_COUNT);
if (!timelapseRunning && NUM_OF_COUNT>0) {
NUM_OF_COUNT--;
}
handler.postDelayed(this, 1000);
}
});
}
}

The CountDownTimer gives out callbacks on the same thread, in which it was created. So the runOnUiThread in onTick is absolutely not required if the CountDownTimer constructor was called on UI thread.
Also,
TextView countdownText = (TextView) findViewById(R.id.countdown);
being called in onTick method is poor design, as findViewById method consumes considerable processing power.
Finally the actual problem as Nabin Bhandari pointed out is the integer value passed to setText method. You need to wrap it to string.
This code is enough
final TextView countdownText = (TextView) findViewById(R.id.countdown);
CountDownTimer timer = new CountDownTimer(15000, 1000) {
#Override
public void onTick(long millisUntilFinished) {
countdownText.setText(String.valueOf(millisUntilFinished/1000));
}
#Override
public void onFinish() {
countdownText.setText("Finished");
}
};
timer.start();

How to automatically Click a Button in Android Every Second

How to automatically Click a Button in Android after a 5 second delay
I tried with the codes that are entered in the link but my application has crashed
My codes;
public class MainActivity extends AppCompatActivity {
Button button;
TextView text;
#Override
protected void onCreate(Bundle savedInstanceState) {
try {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
buttonClick();
Thread timer = new Thread() {
public void run() {
try {
sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
button.performClick();
}
}
};
timer.start();
} catch (Resources.NotFoundException e) {
e.printStackTrace();
}
new Handler().postDelayed(new Runnable() {
#Override
public void run() {
button.performClick();
}
}, 1000);
}
public void buttonClick() {
button=(Button) findViewById(R.id.button);
text=(TextView) findViewById(R.id.text);
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Random s=new Random();
int number=s.nextInt(3);
switch (number)
{case 1:text.setText("1");
break;
case 2: text.setText("2");
break;
}
}
});
}
}
Logcat Error

You need to use
runOnUiThread(new Runnable() {
#Override
public void run() {
}
});
to avoid this error.
Please check Android "Only the original thread that created a view hierarchy can touch its views."
Also you can just use the Handler to perform the button click after a specified amount of time, no need to use the timer.

This is more simpler method to run every second. you dont need to trigger the button. just call the method you want to execute
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Handler handler = new Handler();
Runnable runnable = new Runnable(){
#Override
public void run() {
buttonClick();
if(handler!=null)
handler.postDelayed(runnable, 1000);
}
}
handler.postDelayed(runnable, 1000);
}

start an activity through a method of the class that will be responsible for the running starActivity

good afternoon I have two classes, one that implement one progressBar this class I intend to create a public method that will run startActivity(). the main class would have a button that would call the method. However this giving error null reference.
ProgressBarUtil:
public class ProgressBarUtil extends BaseActionBarActivity {
private ProgressBar progressBar;
private Handler handler;
private int progress;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.progress_bar_util);
inicializaComponentes();
}
public void inicializaComponentes() {
progressBar = (ProgressBar) findViewById(R.id.progressBar);
progressBar.setIndeterminate(true);
handler = new Handler();
executaProgressbar();
}
public void startProgressBar(){
startActivity(new Intent(getBaseContext(),ProgressBarUtil.class));
}
private void executaProgressbar() {
new Thread(new Runnable() {
#Override
public void run() {
try {
Thread.sleep(1000);
finish();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}).start();
}
}
class that will call the method starProgressBar
The other class
#Override
public void onClick(View view) {
int id = view.getId();
if (btnDownload.getId() == id){
new ProgressBarUtil().startProgressBar();
}
}

Where does handler really post its messages to?

I'd like to know the limits and how Handlers work in Android.
I can understand why this works exactly as expected:
public class MainActivity extends Activity {
TextView tv;
Handler mHandler;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mHandler = new Handler();
tv = new TextView(this);
tv.setText("original text");
setContentView(tv);
new Thread(new Runnable() {
#Override
public void run() {
mHandler.post(new Runnable() {
#Override
public void run() {
tv.setText("changing from instance member handler");
}
});
}
}).start();
}
that code, as expected, changes the TextView without complaining for being on wrong thread. i made my handler on UI thread.
however, what i don't understand is... why does THIS also work?
public class MainActivity extends Activity {
TextView tv;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
tv = new TextView(this);
tv.setText("original text");
setContentView(tv);
new Thread(new Runnable() {
Handler handler = new Handler();
#Override
public void run() {
handler.post(new Runnable() {
#Override
public void run() {
tv.setText("changing from different thread.");
}
});
}
}).start();
}
Two questions:
1) I've made my handler from a non-UI thread, but it still updates the textview without complaining about touching a view outside of UI thread. why is that? Where are my messages actually being posted to?
2) say i have 20 pieces of code like that, where i make a new Handler instance each time, will there ever be a problem with running off of UI thread, or a performance issue?
Note: if i made a thread inside of a thread, and instantiate the handler in that inner inner thread, THEN the TextView can't be touched there.

Only code inside run() is executed in another thread. All the initialization is done in the thread that creates the class. And the Runnable is created entirely inside the ui thread.
If you were to write it like
new Thread(new Runnable() {
#Override
public void run() {
Handler handler = new Handler();
handler.post(new Runnable() {
#Override
public void run() {
tv.setText("changing from different thread.");
}
});
}
}).start();
You would get a crash because there is no looper in the thread.