Repeat a task with a time delay

Question

I have a variable in my code say it is  status     I want to display some text in the application depending on this variable value  This has to be done with a specific time delay   It s like    Check status variable value Display some text Wait for 10 seconds Check status variable value Display some text Wait for 15 seconds   and so on  The time delay may vary and it is set once the text is displayed   I have tried Thread sleep time delay  and it failed  Any better way to get this done

User · Answer

Timer works fine  Here  I use Timer to search text after 1 5s and update UI  Hope that helps   private Timer  timer   new Timer      timer schedule new TimerTask          Override     public void run                use runOnUiThread Runnable action          runOnUiThread new Runnable                  Override             public void run                     search                                       timeInterval

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Based on the above post concerning the ScheduledThreadPoolExecutor  I came up with a utility that suited my needs  wanted to fire a method every 3 seconds    class MyActivity       private ScheduledThreadPoolExecutor mDialogDaemon       private void initDebugButtons             Button btnSpawnDialogs    Button findViewById R id btn spawn dialogs           btnSpawnDialogs setVisibility View VISIBLE           btnSpawnDialogs setOnClickListener new OnClickListener                  Override             public void onClick View view                    spawnDialogs                                         private void spawnDialogs             if  mDialogDaemon    null                mDialogDaemon shutdown                mDialogDaemon   null                    mDialogDaemon   new ScheduledThreadPoolExecutor 1              This process will execute immediately  then execute every 3 seconds          mDialogDaemon scheduleAtFixedRate new Runnable                  Override             public void run                     runOnUiThread new Runnable                          Override                     public void run                                Do something worthwhile                                                                    0L  3000L  TimeUnit MILLISECONDS

User · Answer

You should use Handler s postDelayed function for this purpose  It will run your code with specified delay on the main UI thread  so you will be able to update UI controls    private int mInterval   5000     5 seconds by default  can be changed later private Handler mHandler    Override protected void onCreate Bundle bundle            your code here      mHandler   new Handler        startRepeatingTask        Override public void onDestroy         super onDestroy        stopRepeatingTask       Runnable mStatusChecker   new Runnable          Override      public void run               try                  updateStatus      this function can change value of mInterval              finally                     100  guarantee that this always happens  even if                   your update method throws an exception                mHandler postDelayed mStatusChecker  mInterval                         void startRepeatingTask         mStatusChecker run        void stopRepeatingTask         mHandler removeCallbacks mStatusChecker

User · Answer

You can use a Handler to post runnable code   This technique is outlined very nicely here  https   guides codepath com android Repeating-Periodic-Tasks

User · Answer

For people using Kotlin  inazaruk s answer will not work  the IDE will require the variable to be initialized  so instead of using the postDelayed inside the Runnable  we ll use it in an separate method    Initialize your Runnable like this     private var myRunnable   Runnable         Do some work       Magic happens here       runDelayedHandler 1000       Initialize your runDelayedHandler method like this     private fun runDelayedHandler timeToWait   Long        if   keepRunning              Stop your handler         handler removeCallbacksAndMessages null            Do something here  this acts like onHandlerStop           else             Keep it running         handler postDelayed myRunnable  timeToWait           As you can see  this approach will make you able to control the lifetime of the task  keeping track of keepRunning and changing it during the lifetime of the application will do the job for you

User · Answer

There are 3 ways to do it  Use ScheduledThreadPoolExecutor A bit of overkill since you don t need a pool of Thread      ----------------------SCHEDULER-------------------------     private final ScheduledThreadPoolExecutor executor                new ScheduledThreadPoolExecutor 1        ScheduledFuture lt   gt  schedulerFuture     public void  startScheduler            schedulerFuture   executor  scheduleWithFixedDelay new Runnable                  Override             public void run                       DO YOUR THINGS                 pageIndexSwitcher setVisibility View GONE                            0L  5 MILLI SEC   TimeUnit MILLISECONDS               public void  stopScheduler             pageIndexSwitcher setVisibility View VISIBLE           schedulerFuture cancel false           startScheduler           Use Timer Task Old Android Style       ----------------------TIMER  TASK-------------------------      private Timer carousalTimer      private void startTimer             carousalTimer   new Timer       At this line a new Thread will be created         carousalTimer scheduleAtFixedRate new TimerTask                  Override             public void run                       DO YOUR THINGS                 pageIndexSwitcher setVisibility INVISIBLE                            0  5   MILLI SEC      delay            void stopTimer             carousalTimer cancel           Use Handler and Runnable Modern Android Style       ----------------------HANDLER-------------------------      private Handler taskHandler   new android os Handler         private Runnable repeatativeTaskRunnable   new Runnable             public void run                   DO YOUR THINGS                      void startHandler             taskHandler postDelayed repeatativeTaskRunnable  5   MILLI SEC              void stopHandler             taskHandler removeCallbacks repeatativeTaskRunnable          Non-Leaky Handler with Activity   Context Declare an inner Handler class which does not leak Memory in your Activity Fragment class            Instances of static inner classes do not hold an implicit        reference to their outer class              private static class NonLeakyHandler extends Handler           private final WeakReference lt FlashActivity gt  mActivity           public NonLeakyHandler FlashActivity activity                mActivity   new WeakReference lt FlashActivity gt  activity                       Override         public void handleMessage Message msg                FlashActivity activity   mActivity get                if  activity    null                                                          Declare a runnable which will perform your repetitive task in your Activity Fragment class    private Runnable repeatativeTaskRunnable   new Runnable             public void run                 new Handler getMainLooper    post new Runnable                      Override                 public void run                 DO YOUR THINGS                   Initialize Handler object in your Activity Fragment  here FlashActivity is my activity class    Task Handler private Handler taskHandler   new NonLeakyHandler FlashActivity this    To repeat a task after fix time interval  taskHandler postDelayed repeatativeTaskRunnable   DELAY MILLIS    To stop the repetition of task  taskHandler  removeCallbacks repeatativeTaskRunnable     UPDATE  In Kotlin        update interval for widget     override val UPDATE INTERVAL   1000L        Handler to repeat update     private val updateWidgetHandler   Handler          runnable to update widget     private var updateWidgetRunnable  Runnable   Runnable           run                 Update UI             updateWidget                  Re-run it after the update interval             updateWidgetHandler postDelayed updateWidgetRunnable  UPDATE INTERVAL                        SATART updating in foreground  override fun onResume             super onResume           updateWidgetHandler postDelayed updateWidgetRunnable  UPDATE INTERVAL                 REMOVE callback if app in background     override fun onPause             super onPause           updateWidgetHandler removeCallbacks updateWidgetRunnable

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In my case  I had to execute a process if one of these conditions were true  if a previous process was completed or if 5 seconds had already passed  So  I did the following and worked pretty well   private Runnable mStatusChecker  private Handler mHandler   class   method       mStatusChecker   new Runnable                 int times   0               Override             public void run                     if  times  lt  5                        if  process1 isRead                              executeProcess2                          else                           times                            mHandler postDelayed mStatusChecker  1000                                           else                       executeProcess2                                                        mHandler   new Handler            startRepeatingTask           void startRepeatingTask            mStatusChecker run               void stopRepeatingTask             mHandler removeCallbacks mStatusChecker               If process1 is read  it executes process2  If not  it increments the variable times  and make the Handler be executed after one second  It maintains a loop until process1 is read or times is 5  When times is 5  it means that 5 seconds passed and in each second  the if clause of process1 isRead   is executed

User · Answer

To anyone interested  here s a class I created using inazaruk s code that creates everything needed  I called it UIUpdater because I use it to periodically update the UI  but you can call it anything you like    import android os Handler         A class used to perform periodical updates     specified inside a runnable object  An update interval    may be specified  otherwise  the class will perform the     update every 2 seconds           author Carlos Sim  es     public class UIUpdater              Create a Handler that uses the Main Looper to run in         private Handler mHandler   new Handler Looper getMainLooper              private Runnable mStatusChecker          private int UPDATE INTERVAL   2000                          Creates an UIUpdater object  that can be used to            perform UIUpdates on a specified time interval                          param uiUpdater A runnable containing the update routine                      public UIUpdater final Runnable uiUpdater                mStatusChecker   new Runnable                      Override                 public void run                            Run the passed runnable                     uiUpdater run                           Re-run it after the update interval                     mHandler postDelayed this  UPDATE INTERVAL                                                                      The same as the default constructor  but specifying the            intended update interval                          param uiUpdater A runnable containing the update routine              param interval  The interval over which the routine                             should run  milliseconds                       public UIUpdater Runnable uiUpdater  int interval               UPDATE INTERVAL   interval              this uiUpdater                                     Starts the periodical update routine  mStatusChecker             adds the callback to the handler                       public synchronized void startUpdates                mStatusChecker run                                      Stops the periodical update routine from running             by removing the callback                      public synchronized void stopUpdates                mHandler removeCallbacks mStatusChecker                 You can then create a UIUpdater object inside your class and use it like so       mUIUpdater   new UIUpdater new Runnable               Override           public void run                    do stuff                            Start updates mUIUpdater startUpdates        Stop updates mUIUpdater stopUpdates          If you want to use this as an activity updater  put the start call inside the onResume   method and the stop call inside the onPause    so the updates start and stop according to the activity visibility

User · Answer

Using kotlin and its Coroutine its quite easy  first declare a job in your class  better in your viewModel  like this   private var repeatableJob  Job    null   then when you want to create and start it do this   repeatableJob   viewModelScope launch       while  isActive             delay 5 000           loadAlbums iImageAPI  titleHeader  true          repeatableJob  start     and if you want to finish it   repeatableJob  cancel     PS  viewModelScope is only available in view models  you can use other Coroutine scopes such as withContext Dispatchers IO   More information  Here

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I think the new hotness is to use a ScheduledThreadPoolExecutor  Like so   private final ScheduledThreadPoolExecutor executor             new ScheduledThreadPoolExecutor 1   this executor  scheduleWithFixedDelay new Runnable      Override public void run         update             0L  kPeriod  kTimeUnit

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Timer is another way to do your work but be quiet sure to add runOnUiThread if you are working with UI       import java text SimpleDateFormat  import java util Calendar  import java util Timer  import java util TimerTask   import android os Bundle  import android view View  import android view View OnClickListener  import android widget Button  import android widget CheckBox  import android widget TextView  import android app Activity   public class MainActivity extends Activity     CheckBox optSingleShot   Button btnStart  btnCancel   TextView textCounter    Timer timer   MyTimerTask myTimerTask     Override  protected void onCreate Bundle savedInstanceState      super onCreate savedInstanceState     setContentView R layout activity main     optSingleShot    CheckBox findViewById R id singleshot     btnStart    Button findViewById R id start     btnCancel    Button findViewById R id cancel     textCounter    TextView findViewById R id counter      btnStart setOnClickListener new OnClickListener         Override    public void onClick View arg0         if timer    null        timer cancel                 re-schedule timer here       otherwise  IllegalStateException of        TimerTask is scheduled already         will be thrown     timer   new Timer        myTimerTask   new MyTimerTask         if optSingleShot isChecked            singleshot delay 1000 ms      timer schedule myTimerTask  1000        else         delay 1000ms  repeat in 5000ms      timer schedule myTimerTask  1000  5000                    btnCancel setOnClickListener new OnClickListener         Override    public void onClick View v        if  timer  null        timer cancel         timer   null                         class MyTimerTask extends TimerTask       Override   public void run        Calendar calendar   Calendar getInstance       SimpleDateFormat simpleDateFormat         new SimpleDateFormat  dd MMMM yyyy HH mm ss a       final String strDate   simpleDateFormat format calendar getTime         runOnUiThread new Runnable          Override     public void run          textCounter setText strDate                         and xml is      lt LinearLayout xmlns android  http   schemas android com apk res android  xmlns tools  http   schemas android com tools  android layout width  match parent  android layout height  match parent  android paddingBottom   dimen activity vertical margin  android paddingLeft   dimen activity horizontal margin  android paddingRight   dimen activity horizontal margin  android paddingTop   dimen activity vertical margin  android orientation  vertical  tools context   MainActivity   gt    lt TextView     android layout width  wrap content      android layout height  wrap content      android layout gravity  center horizontal      android autoLink  web      android text  http   android-er blogspot com       android textStyle  bold    gt   lt CheckBox      android id    id singleshot      android layout width  wrap content      android layout height  wrap content      android text  Single Shot   gt                 Another Way to use CountDownTimer   new CountDownTimer 30000  1000          public void onTick long millisUntilFinished             mTextField setText  seconds remaining      millisUntilFinished   1000                public void onFinish              mTextField setText  done                start      Schedule a countdown until a time in the future  with regular notifications on intervals along the way  Example of showing a 30 second countdown in a text field   For Details

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Try following example it works      Use  Handler  in onCreate   method which makes use of postDelayed   method that Causes the Runnable to be added to the message queue  to be run after the specified amount of time elapses that is 0 in given example  1  Refer this code     public void onCreate Bundle savedInstanceState        super onCreate savedInstanceState          setContentView R layout main         ------------------       ------------------     android os Handler customHandler   new android os Handler                customHandler postDelayed updateTimerThread  0      private Runnable updateTimerThread   new Runnable             public void run                           write here whaterver you want to repeat             customHandler postDelayed this  1000

[android] Repeat a task with a time delay?

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