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Tuesday, 17 December 2013

Handler vs Timer : fixed-period execution and fixed-rate execution android development

In Android Timer and Handler are both can be used for repetitive call. We can do same piece of task using either Timer or Handler (With runnable). First going to pros and cos of each we should look what documentation says about both. Its very important to avoid memory leak in android application

Timer Recurring tasks are scheduled with either a fixed period or a fixed rate:
  • With the default fixed-period execution, each successive run of a task is scheduled relative to the start time of the previous run, so two runs are never fired closer together in time than the specified period.
   • With fixed-rate execution, the start time of each successive run of a task is scheduled without regard for when the previous run took place. This may result in a series of bunched-up runs (one launched immediately after another) if delays prevent the timer from starting tasks on time.

Handler  

  • to schedule messages and runnables to be executed as some point in the future; and 
  • to enqueue an action to be performed on a different thread than your own.


Handler Implementation


  • How to create repetitive task using Handler

  Handler mHandler;
  public void useHandler() {
    mHandler = new Handler();
    mHandler.postDelayed(mRunnable, 1000);
  }

  private Runnable mRunnable = new Runnable() {

    @Override
    public void run() {
      Log.e("Handlers", "Calls");
      /** Do something **/
      mHandler.postDelayed(mRunnable, 1000);
    }
  };

  • How to remove pending execution from Handler

       mHandler.removeCallbacks(mRunnable);

  • How to schedule it again

      mHandler.postDelayed(mRunnable, 1000);


  • Where to perform Task

      Runnable works under UI thread so you can update UserInterface in Handler respective Runnable


Timer Implementation


  • How to create repetitive task using Timer

  public void useTimer() {
    Timer mTimer = new Timer();
    mTimer.cancel();
    mTimer.schedule(new TimerTask() {

      @Override
      public void run() {
        Log.e("Timer", "Calls");
      }
    }, 1000, 1000);
  }


  • How to remove pending execution from Timer

      mTimer.cancel(); will cancel all the schedule task.

  • How to schedule it again

        You can not reschedule Timer again. So you to create object of timer again if you are trying to reschedule its task.


Comparison Handler VS Timer


  • While rescheduling Handler is very easy, you can not reschedule Timer


  • In Handler you can attach to any Runnable but Timer schedule for only one TimerTask


  • TimerTask is purely background task so you can not update UserInterface, but that's not true for Handler's Runnables
Timer Cause Execption


  • Timer tends to leak more memory compare to Handler see the graph of object retains by timer and Handler. It will increase rapidly for Timer if you are creating and scheduling new task.

Handler Memory Graph

Timer Memory Graph
Which one to use Obviously i will recommend to use Handler with Runnable
Android News and source code