How to run a Runnable thread in Android at defined intervals

Question

I developed an application to display some text at defined intervals in the Android emulator screen  I am using the Handler class  Here is a snippet from my code   handler   new Handler    Runnable r   new Runnable         public void run             tv append  Hello World                            handler postDelayed r  1000     When I run this application the text is displayed only once  Why

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now in Kotlin you can run threads this way   class SimpleRunnable  Runnable       public override fun run             println    Thread currentThread    has run            fun main args  Array lt String gt         val thread   SimpleThread       thread start      Will output  Thread Thread-0 5 main  has run      val runnable   SimpleRunnable       val thread1   Thread runnable      thread1 start      Will output  Thread Thread-1 5 main  has run

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I believe for this typical case  i e  to run something with a fixed interval  Timer is more appropriate  Here is a simple example   myTimer   new Timer    myTimer schedule new TimerTask                Override public void run            If you want to modify a view in your Activity     MyActivity this runOnUiThread new Runnable           public void run                tv append  Hello World                         1000  1000      initial delay 1 second  interval 1 second   Using Timer has few advantages    Initial delay and the interval can be easily specified in the schedule function arguments The timer can be stopped by simply calling myTimer cancel   If you want to have only one thread running  remember to call myTimer cancel   before scheduling a new one  if myTimer is not null

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I think can improve first solution of Alex2k8 for update correct each second  1 Original code   public void run         tv append  Hello World        handler postDelayed this  1000       2 Analysis   In above cost  assume tv append  Hello Word   cost T milliseconds  after display 500 times delayed time is 500 T milliseconds It will increase delayed when run long time   3  Solution  To avoid that Just change order of postDelayed    to avoid delayed   public void run         handler postDelayed this  1000       tv append  Hello World

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Handler handler new Handler    Runnable r   new Runnable        public void run             tv append  Hello World                                   handler postDelayed r  1000             handler post r

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The simple fix to your example is    handler   new Handler     final Runnable r   new Runnable         public void run             tv append  Hello World            handler postDelayed this  1000             handler postDelayed r  1000     Or we can use normal thread for example  with original Runner     Thread thread   new Thread          Override     public void run             try               while true                    sleep 1000                   handler post this                           catch  InterruptedException e                e printStackTrace                        thread start      You may consider your runnable object just as a command that can be sent to the message queue for execution  and handler as just a helper object used to send that command   More details are here http   developer android com reference android os Handler html

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Kotlin  private lateinit var runnable  Runnable override fun onCreate savedInstanceState  Bundle         val handler   Handler       runnable   Runnable              do your work         handler postDelayed runnable  2000            handler postDelayed runnable  2000      Java  Runnable runnable  Handler handler    Override protected void onCreate  Nullable Bundle savedInstanceState        handler   new Handler        runnable   new Runnable              Override         public void run                    do your work             handler postDelayed this  1000                        handler postDelayed runnable  1000

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An interesting example is you can continuously see a counter stop-watch running in separate thread  Also showing GPS-Location  While main activity User Interface Thread is already there   Excerpt   try           cnt    scnt        now System currentTimeMillis        r rand nextInt 6   r            loc lm getLastKnownLocation best            if loc  null             lat loc getLatitude            lng loc getLongitude                    Thread sleep 100        handler sendMessage handler obtainMessage       catch  InterruptedException e           Toast makeText this   Error   e toString    Toast LENGTH LONG  show        To look at code see here   Thread example displaying GPS Location and Current Time runnable alongside main-activity s User Interface Thread

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For repeating task you can use  new Timer   scheduleAtFixedRate task  runAfterADelayForFirstTime  repeaingTimeInterval     call it like   new Timer   scheduleAtFixedRate new TimerTask                  Override             public void run                              500 1000        The above code will run first time after half second 500  and repeat itself after each second 1000    Where   task being the method to be executed  after the time to initial execution      interval the time for repeating the execution   Secondly  And you can also use CountDownTimer if you want to execute a Task number of times       new CountDownTimer 40000  1000      40000 milli seconds is total time  1000 milli seconds is time interval       public void onTick long millisUntilFinished                  public void onFinish                  start       Above codes run 40 times after each second   And you can also do it with runnable  create a runnable method like   Runnable runnable   new Runnable                  Override         public void run                                 And call it in both these ways  new Handler   postDelayed runnable  500     where 500 is delayMillis     to work on mainThread   OR  new Thread runnable  start     to work in Background

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If I understand correctly the documentation of Handler post   method      Causes the Runnable r to be added to the message queue  The runnable will be run on the thread to which this handler is attached    So examples provided by  alex2k8  even though are working correctly  are not the same  In case  where Handler post   is used  no new threads are created  You just post Runnable to the thread with Handler to be executed by EDT  After that  EDT only executes Runnable run    nothing else   Remember  Runnable    Thread

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Kotlin with Coroutines  In Kotlin  using coroutines you can do the following   CoroutineScope Dispatchers Main  launch      Main  because UI is changed     ticker delayMillis   1000  initialDelayMillis   1000  consumeEach           tv append  Hello World             Try it out here

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new Handler   postDelayed new Runnable         public void run                do something                           100

[android] How to run a Runnable thread in Android at defined intervals?

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