Develop Reference

How to add a timer/clock in android studio [duplicate]

I want to be able to call the following method after a specified delay.
In objective c there was something like:
[self performSelector:#selector(DoSomething) withObject:nil afterDelay:5];
Is there an equivalent of this method in android with java?
For example I need to be able to call a method after 5 seconds.
public void DoSomething()
{
//do something here
}

Kotlin
Handler(Looper.getMainLooper()).postDelayed({
//Do something after 100ms
}, 100)
Java
final Handler handler = new Handler(Looper.getMainLooper());
handler.postDelayed(new Runnable() {
#Override
public void run() {
//Do something after 100ms
}
}, 100);
The class to import is android.os.handler.

I couldn't use any of the other answers in my case.
I used the native java Timer instead.
new Timer().schedule(new TimerTask() {
#Override
public void run() {
// this code will be executed after 2 seconds
}
}, 2000);

Note: This answer was given when the question didn't specify Android as the context. For an answer specific to the Android UI thread look here.
It looks like the Mac OS API lets the current thread continue, and schedules the task to run asynchronously. In the Java, the equivalent function is provided by the java.util.concurrent package. I'm not sure what limitations Android might impose.
private static final ScheduledExecutorService worker =
Executors.newSingleThreadScheduledExecutor();
void someMethod() {
⋮
Runnable task = new Runnable() {
public void run() {
/* Do something… */
}
};
worker.schedule(task, 5, TimeUnit.SECONDS);
⋮
}

For executing something in the UI Thread after 5 seconds:
new Handler(Looper.getMainLooper()).postDelayed(new Runnable() {
#Override
public void run() {
//Do something here
}
}, 5000);

Kotlin & Java Many Ways
1. Using Handler
Handler().postDelayed({
TODO("Do something")
}, 2000)
2. Using TimerTask
Timer().schedule(object : TimerTask() {
override fun run() {
TODO("Do something")
}
}, 2000)
Or even shorter
Timer().schedule(timerTask {
TODO("Do something")
}, 2000)
Or shortest would be
Timer().schedule(2000) {
TODO("Do something")
}
3. Using Executors
Executors.newSingleThreadScheduledExecutor().schedule({
TODO("Do something")
}, 2, TimeUnit.SECONDS)
In Java
1. Using Handler
new Handler().postDelayed(new Runnable() {
#Override
public void run() {
//Do something
}
}, 2000);
2. Using Timer
new Timer().schedule(new TimerTask() {
#Override
public void run() {
// Do something
}
}, 2000);
3. Using ScheduledExecutorService
private static final ScheduledExecutorService worker = Executors.newSingleThreadScheduledExecutor();
Runnable runnable = new Runnable() {
public void run() {
// Do something
}
};
worker.schedule(runnable, 2, TimeUnit.SECONDS);

you can use Handler inside UIThread:
runOnUiThread(new Runnable() {
#Override
public void run() {
new Handler().postDelayed(new Runnable() {
#Override
public void run() {
//add your code here
}
}, 1000);
}
});

Thanks for all the great answers, I found a solution that best suits my needs.
Handler myHandler = new DoSomething();
Message m = new Message();
m.obj = c;//passing a parameter here
myHandler.sendMessageDelayed(m, 1000);
class DoSomething extends Handler {
#Override
public void handleMessage(Message msg) {
MyObject o = (MyObject) msg.obj;
//do something here
}
}

See this demo:
import java.util.Timer;
import java.util.TimerTask;
class Test {
public static void main( String [] args ) {
int delay = 5000;// in ms
Timer timer = new Timer();
timer.schedule( new TimerTask(){
public void run() {
System.out.println("Wait, what..:");
}
}, delay);
System.out.println("Would it run?");
}
}

More Safety - With Kotlin Coroutine
Most of the answers use Handler but I give a different solution to delay in activity, fragment, view model with Android Lifecycle ext. This way will auto cancel when the lifecycle begins destroyed - avoid leaking the memory or crashed app
In Activity or Fragment:
lifecycleScope.launch {
delay(DELAY_MS)
doSomething()
}
In ViewModel:
viewModelScope.lanch {
delay(DELAY_MS)
doSomething()
}
In suspend function: (Kotlin Coroutine)
suspend fun doSomethingAfter(){
delay(DELAY_MS)
doSomething()
}
If you get an error with the lifecycleScope not found! - import this dependency to the app gradle file:
implementation "androidx.lifecycle:lifecycle-runtime-ktx:2.4.0"

If you have to use the Handler, but you are into another thread, you can use runonuithread to run the handler in UI thread. This will save you from Exceptions thrown asking to call Looper.Prepare()
runOnUiThread(new Runnable() {
#Override
public void run() {
new Handler().postDelayed(new Runnable() {
#Override
public void run() {
//Do something after 1 second
}
}, 1000);
}
});
Looks quite messy, but this is one of the way.

I prefer to use View.postDelayed() method, simple code below:
mView.postDelayed(new Runnable() {
#Override
public void run() {
// Do something after 1000 ms
}
}, 1000);

Here is my shortest solution:
new Handler().postDelayed(new Runnable() {
#Override
public void run() {
//Do something after 100ms
}
}, 100);

If you are using Android Studio 3.0 and above you can use lambda expressions. The method callMyMethod() is called after 2 seconds:
new Handler().postDelayed(() -> callMyMethod(), 2000);
In case you need to cancel the delayed runnable use this:
Handler handler = new Handler();
handler.postDelayed(() -> callMyMethod(), 2000);
// When you need to cancel all your posted runnables just use:
handler.removeCallbacksAndMessages(null);

final Handler handler = new Handler();
Timer t = new Timer();
t.schedule(new TimerTask() {
public void run() {
handler.post(new Runnable() {
public void run() {
//DO SOME ACTIONS HERE , THIS ACTIONS WILL WILL EXECUTE AFTER 5 SECONDS...
}
});
}
}, 5000);

I suggest the Timer, it allows you to schedule a method to be called on a very specific interval. This will not block your UI, and keep your app resonsive while the method is being executed.
The other option, is the wait(); method, this will block the current thread for the specified length of time. This will cause your UI to stop responding if you do this on the UI thread.

So there are a few things to consider here as there are so many ways to skin this cat. Although answers have all already been given selected and chosen. I think it's important that this gets revisited with proper coding guidelines to avoid anyone going the wrong direction just because of "majority selected simple answer".
So first let's discuss the simple Post Delayed answer that is the winner selected answer overall in this thread.
A couple of things to consider. After the post delay, you can encounter memory leaks, dead objects, life cycles that have gone away, and more. So handling it properly is important as well. You can do this in a couple of ways.
For sake of modern development, I'll supply in KOTLIN
Here is a simple example of using the UI thread on a callback and confirming that your activity is still alive and well when you hit your callback.
Handler(Looper.getMainLooper()).postDelayed({
if(activity != null && activity?.isFinishing == false){
txtNewInfo.visibility = View.GONE
}
}, NEW_INFO_SHOW_TIMEOUT_MS)
However, this is still not perfect as there is no reason to hit your callback if the activity has gone away. so a better way would be to keep a reference to it and remove it's callbacks like this.
private fun showFacebookStylePlus1NewsFeedOnPushReceived(){
A35Log.v(TAG, "showFacebookStylePlus1NewsFeedOnPushReceived")
if(activity != null && activity?.isFinishing == false){
txtNewInfo.visibility = View.VISIBLE
mHandler.postDelayed({
if(activity != null && activity?.isFinishing == false){
txtNewInfo.visibility = View.GONE
}
}, NEW_INFO_SHOW_TIMEOUT_MS)
}
}
and of course handle cleanup on the onPause so it doesn't hit the callback.
override fun onPause() {
super.onPause()
mHandler.removeCallbacks(null)
}
Now that we have talked through the obvious, let's talk about a cleaner option with modern day coroutines and kotlin :). If you aren't using these yet, you are really missing out.
fun doActionAfterDelay()
launch(UI) {
delay(MS_TO_DELAY)
actionToTake()
}
}
or if you want to always do a UI launch on that method you can simply do:
fun doActionAfterDelay() = launch(UI){
delay(MS_TO_DELAY)
actionToTake()
}
Of course just like the PostDelayed you have to make sure you handle canceling so you can either do the activity checks after the delay call or you can cancel it in the onPause just like the other route.
var mDelayedJob: Job? = null
fun doActionAfterDelay()
mDelayedJob = launch(UI) {
try {
delay(MS_TO_DELAY)
actionToTake()
}catch(ex: JobCancellationException){
showFancyToast("Delayed Job canceled", true, FancyToast.ERROR, "Delayed Job canceled: ${ex.message}")
}
}
}
}
//handle cleanup
override fun onPause() {
super.onPause()
if(mDelayedJob != null && mDelayedJob!!.isActive) {
A35Log.v(mClassTag, "canceling delayed job")
mDelayedJob?.cancel() //this should throw CancelationException in coroutine, you can catch and handle appropriately
}
}
If you put the launch(UI) into the method signature the job can be assigned in the calling line of code.
so moral of the story is to be safe with your delayed actions, make sure you remove your callbacks, or cancel your jobs and of course confirm you have the right life cycle to touch items on your delay callback complete. The Coroutines also offers cancelable actions.
Also worth noting that you should typically handle the various exceptions that can come with coroutines. For example, a cancelation, an exception, a timeout, whatever you decide to use. Here is a more advanced example if you decide to really start utilizing coroutines.
mLoadJob = launch(UI){
try {
//Applies timeout
withTimeout(4000) {
//Moves to background thread
withContext(DefaultDispatcher) {
mDeviceModelList.addArrayList(SSDBHelper.getAllDevices())
}
}
//Continues after async with context above
showFancyToast("Loading complete", true, FancyToast.SUCCESS)
}catch(ex: JobCancellationException){
showFancyToast("Save canceled", true, FancyToast.ERROR, "Save canceled: ${ex.message}")
}catch (ex: TimeoutCancellationException) {
showFancyToast("Timed out saving, please try again or press back", true, FancyToast.ERROR, "Timed out saving to database: ${ex.message}")
}catch(ex: Exception){
showFancyToast("Error saving to database, please try again or press back", true, FancyToast.ERROR, "Error saving to database: ${ex.message}")
}
}

For a Simple line Handle Post delay, you can do as following :
new Handler().postDelayed(new Runnable() {
#Override
public void run() {
// Do someting
}
}, 3000);
I hope this helps

You can use this for Simplest Solution:
new Handler().postDelayed(new Runnable() {
#Override
public void run() {
//Write your code here
}
}, 5000); //Timer is in ms here.
Else, Below can be another clean useful solution:
new Handler().postDelayed(() ->
{/*Do something here*/},
5000); //time in ms

You can make it much cleaner by using the newly introduced lambda expressions:
new Handler().postDelayed(() -> {/*your code here*/}, time);

Using Kotlin, we can achieve by doing the following
Handler().postDelayed({
// do something after 1000ms
}, 1000)

If you use RxAndroid then thread and error handling becomes much easier. Following code executes after a delay
Observable.timer(delay, TimeUnit.SECONDS)
.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(aLong -> {
// Execute code here
}, Throwable::printStackTrace);

I created simpler method to call this.
public static void CallWithDelay(long miliseconds, final Activity activity, final String methodName)
{
new Handler().postDelayed(new Runnable() {
#Override
public void run() {
try {
Method method = activity.getClass().getMethod(methodName);
method.invoke(activity);
} catch (NoSuchMethodException e) {
e.printStackTrace();
} catch (InvocationTargetException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
}
}
}, miliseconds);
}
To use it, just call : .CallWithDelay(5000, this, "DoSomething");

Below one works when you get,
java.lang.RuntimeException: Can't create handler inside thread that
has not called Looper.prepare()
final Handler handler = new Handler(Looper.getMainLooper());
handler.postDelayed(new Runnable() {
#Override
public void run() {
//Do something after 100ms
}
}, 100);

It's very easy using the CountDownTimer.
For more details https://developer.android.com/reference/android/os/CountDownTimer.html
import android.os.CountDownTimer;
// calls onTick every second, finishes after 3 seconds
new CountDownTimer(3000, 1000) {
public void onTick(long millisUntilFinished) {
Log.d("log", millisUntilFinished / 1000);
}
public void onFinish() {
// called after count down is finished
}
}.start();

I like things cleaner:
Here is my implementation, inline code to use inside your method
new Handler().postDelayed(new Runnable() {
#Override
public void run() {
//Do something after 100ms
}
}, 100);

everybody seems to forget to clean the Handler before posting a new runnable or message on it. Otherway they could potentially accumulate and cause bad behaviour.
handler.removeMessages(int what);
// Remove any pending posts of messages with code 'what' that are in the message queue.
handler.removeCallbacks(Runnable r)
// Remove any pending posts of Runnable r that are in the message queue.

Here is another tricky way: it won't throw exception when the runnable change UI elements.
public class SimpleDelayAnimation extends Animation implements Animation.AnimationListener {
Runnable callBack;
public SimpleDelayAnimation(Runnable runnable, int delayTimeMilli) {
setDuration(delayTimeMilli);
callBack = runnable;
setAnimationListener(this);
}
#Override
public void onAnimationStart(Animation animation) {
}
#Override
public void onAnimationEnd(Animation animation) {
callBack.run();
}
#Override
public void onAnimationRepeat(Animation animation) {
}
}
You can call the animation like this:
view.startAnimation(new SimpleDelayAnimation(delayRunnable, 500));
Animation can attach to any view.

Here is the answer in Kotlin you lazy, lazy people:
Handler().postDelayed({
//doSomethingHere()
}, 1000)

Kotlin
runOnUiThread from a Fragment
Timer
example:
Timer().schedule(500) {
activity?.runOnUiThread {
// code
}
}

A suitable solution in android:
private static long SLEEP_TIME = 2 // for 2 second
.
.
MyLauncher launcher = new MyLauncher();
launcher.start();
.
.
private class MyLauncher extends Thread {
#Override
/**
* Sleep for 2 seconds as you can also change SLEEP_TIME 2 to any.
*/
public void run() {
try {
// Sleeping
Thread.sleep(SLEEP_TIME * 1000);
} catch (Exception e) {
Log.e(TAG, e.getMessage());
}
//do something you want to do
//And your code will be executed after 2 second
}
}

How to sleep only after executing a command?

I have a DialogFragment, with a public interface and a method to save the callback:
public class ChooseExportTypeDialogFragment extends DialogFragment{
public interface ExportTypeClickListener{
public void doPositiveClick(ExportTypeEnum exportType);
}
public void setOnConfirmClickListener( ExportTypeClickListener callback ){
this.callback = callback;
}
//...
}
I declare a DialogFragment like this:
final ChooseExportTypeDialogFragment chooseExportTypeDialogFragment = new ChooseExportTypeDialogFragment();
chooseExportTypeDialogFragment.setOnConfirmClickListener( new ExportTypeClickListener() {
#Override
public void doPositiveClick( ExportTypeEnum exportType ) {
toast.setText("Preparing Export...");
toast.show();
controller.onExport( adapter.getSelected() , exportType);
chooseExportTypeDialogFragment.dismiss();
}
} );
chooseExportTypeDialogFragment.show( controller.getSupportFragmentManager(), "notification" );
In the method onExport(), I perform a Thread.sleep(3000) (among other things).
It seems that when doPositiveClick() is invoked, the sleeping (which is in onExport()) occurs before toast.show(). I tried to put both operations (toast.show() and .onExport()) in synchronized blocks, hoping the sleep will start only after finishing toast.show(), but the same problem happens.
I also tried putting toast.show() in a thread, then .start() it and .join() it. And only then call onExport(). Same problem
How can I show the toast and only then let onExport() start?

Thread.sleep is rather problematic in Android espessially when performed in the UI thread because it can cause other elements (in your case Toast) to stop responding. An alternative to your problem is to execute your controller.onExport() logic inside a handler.
#Override
public void doPositiveClick( ExportTypeEnum exportType ){
toast.setText("Preparing Export...");
toast.show();
final Handler handler = new Handler();
handler.postDelayed(new Runnable() {
#Override
public void run() {
controller.onExport( adapter.getSelected() , exportType);
}
}, 3500);
chooseExportTypeDialogFragment.dismiss();
}
You might also need to disable clickability of your Dialog buttons while waiting for the toast text to finish.

Android thread error - Can't create handler inside thread that has not called Looper.prepare()

I am trying to get a timer to run in a separate thread.
I have the following declaration before my onCreate function:
TimerTask scanTask;
Timer t = new Timer();
Then the following code within onCreate:
Runnable runnable = new Runnable() {
#Override
public void run() {
scanTask = new TimerTask() {
#Override
public void run() {
System.out.println("timer test");
}
};
t.schedule(scanTask, 0, 5000);
CountDownTimer waitTimer;
waitTimer = new CountDownTimer(20000,300) {
#Override
public void onTick(long l) {
}
#Override
public void onFinish() {
t.cancel();
System.out.println("Timer stopped");
}
}.start();
}
};
Thread periodic_scan = new Thread(runnable);
periodic_scan.start();
However, when I run the app, it crashes and gives me the error:
java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
I'm not sure I completely understand why this error is occurring. Is it something to do with the UI thread? Also, I'm not sure whether the way I've tried to implement this is correct. This is my first time trying to deal with threads in Android.

you can use HandlerThread like
HandlerThread handlerThread = new HandlerThread("name");
handlerThread.start();
Handler threadHandler = new Handler(handlerThread.getLooper(),new Callback() {
public boolean handleMessage(Message msg) {
return true;
}
});

I ended up changing the code a bit and decided to use a Thread class:
class TimerThread extends Thread {
TimerTask scanTask;
Timer t = new Timer();
#Override
public void run() {
Looper.prepare();
scanTask = new TimerTask() {
public void run() {
System.out.println("timer test");
}
};
t.schedule(scanTask, 0, 5000);
CountDownTimer waitTimer;
waitTimer = new CountDownTimer(20000,300) {
#Override
public void onTick(long l) {
}
#Override
public void onFinish() {
t.cancel();
System.out.println("Timer stopped");
}
}.start();
Looper.loop();
}
}
In onCreate I used the following:
new TimerThread().start();
The program now works without any errors, however the only problem now is that there is a noticeable 2-3 second lag when the program loads up before the UI renders to the screen.
I'm not sure why this is happening if the timer function I am using is running on a separate thread, unless I've missed something here...

If you create a handler (or any class you call creates a handler) it needs to be in a Thread that has a Looper on it, and has called Looper.prepare(). Either TimerTask or CountDownTimer is doing that. How to fix it depends on where you want the events to be posted to. If you want them on the UI thread, you'll have to create the handler on the UI thread. If you want them on this thread, then you need to call Looper.prepare and Looper.loop at some point.
The UI thread already has a looper (the framework starts it for you) so its always ok to make handlers there.

Java Timer equivalent in Android

I recently began working with Java and am exploring Android development. I was trying to port over one of the Java programs I made, but I am having some difficulty with getting the java Timer to function the same way in Android. I read through a number of posts and they, for the most part, indicated that it would be better to use the Handler class in android as opposed to Timer.
This was my timer in Java:
playTimer = new Timer(1000/model.getFPS(), new ActionListener() {
public void actionPerformed(ActionEvent evt) {
// do something
...
if( finished everything ) playTimer.stop();
}
});
And once a certain button was clicked, I would simply run "playTimer.start()" to start it.
As you can see, I had it set up so that the user could set the FPS they wanted (by simply setting the first parameter of the Timer class to 1000/model.getFPS()).
Now I've tried to do something similar in Android using handlers, but I am having some difficulty. It appears that the Handler ticks are not firing at the proper intervals. It seems that they are quite slow compared to what I need it to be. This is what I did in android so far:
public void startTimer() {
playHandler = new Handler();
startTime = System.currentTimeMillis();
playHandler.removeCallbacks(updateTimeTask);
playHandler.postDelayed(updateTimeTask, 0);
}
private Runnable updateTimeTask = new Runnable() {
public void run() {
// do something
...
if( finished everything ) playHander.cancel();
else {
playHandler.postDelayed(updateTimeTask, 1000/model.getFPS());
}
}
};
Excuse the semi-pseudocode. Can anyone shed any light? Thanks guys.

You can use a timer as below. The timer runs every second incrementing the counter. Displs the counter value in textview.
Timer runs on a different thread. SO you should set the text on the UI Thread.
The counter runs from 0 to 99. After 99 the timer is cancelled. Also cancel the timer when not required like in onPause().
public class MainActivity extends Activity {
TextView _tv,tv2;
Timer _t;
int _count=0;
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
_tv = (TextView) findViewById( R.id.textView1 );
_t = new Timer();
_tv.setText(R.string.app_name);
_t.scheduleAtFixedRate( new TimerTask() {
#Override
public void run() {
_count++;
runOnUiThread(new Runnable() //run on ui thread
{
public void run()
{
_tv.setText(""+_count);
if(_count==99)
{
_t.cancel();
}
}
});
}
}, 1000, 1000 ); //change this value of 1000 to whatever you need.
}
#Override
protected void onPause() {
// TODO Auto-generated method stub
super.onPause();
_t.cancel();
}
}

If you decide not to use Timer (for whatever reason) you can just write a separate Thread that sleeps for x milliseconds and then wakes up and calls whatever Runnable you want it to call. That's going to be pretty precise. I have it working at the 10 millisecond level and it works quite nicely.
Just remember that it HAS to call a Runnable because a separate Thread can't have direct effect on anything on the main display thread.
public boolean keepPlayingAnimation = true
Handler h = new Handler()
Runnable updateDisplay = new Runnable(){
public void run(){
//do something in my display;
}
}
new Thread(){
public void run(){
while(keepPlayingAnimation){
try{
sleep(10);
}catch(Exception e){
}
h.post(updateDisplay);
}
}
}.start();
Just don't forget to set keepPlayingAnimation to false when you're done with this cause otherwise it will sit there running in the background for ever (or just about).

Take a look at Android Timer
It already has everything you need i guess. From ticking every 1 second to finish handly and so on.
Here is an example how to setup an TimerTask: setup
Not sure if you need such but i just remembered that i made this.

Can't create handler inside threads that has not called looper?

I want to send a notification after 5 seconds.
I found this code example to do something after 5 seconds, but I just can set a Log.e().
The Notification method is also working. But if I want to call the method setNotification(), I get a RuntimeError after 5 seconds:
Can't create Handler inside Thread that has not called looper.prepare().
I found very much help, but nothing works. So I hope you can help me.
public class Reminder {
Timer timer;
public Reminder(int seconds) {
timer = new Timer();
timer.schedule(new RemindTask(), seconds * 1000);
}
}
class RemindTask extends TimerTask {
public void run() {
todo_list rem = new todo_list();
rem.setNotification("Todo!", false, 1);
}
}
public class todo_list extends ListActivity {
public void onCreate(Bundle savedInstanceState) {
new Reminder(5);
}
public void setNotification(String text, boolean ongoing, int id) {}
}

You need to call rem.setNotification from a thread which will keep running always. One way is to use runonuithread
runonUithread(new Runnable(){
run(){
rem.setNotification("Todo!",false,1);
}
});

You'll get this error when you execute some code that shouldn't be done in another thread than the UI thread. So simple get an activity object and call runOnUiThread(Runnable action) {} on it. Place that code that generates the error in the Runnable.
I hope this helps.