Android - running a method periodically using postDelayed() call

Question

I have a situation in an Android app where I want to start a network activity (sending out some data) which should run every second. I achieve this as follows:

In the onCreate() I have the code:

tv = new TextView(this);
tv.postDelayed(sendData, 1000);

The sendData() function:

   Handler handler = new Handler();
   private Runnable sendData=new Runnable(){
    public void run(){
        try {
            //prepare and send the data here..
            handler.removeCallbacks(sendData);
            handler.postDelayed(sendData, 1000);    
        }
        catch (Exception e) {
            e.printStackTrace();
        }   
    }
};

The problem come in like this: When user presses the back buttons and app comes out (UI disappears) the sendData() function still gets executed which is what I want. Now when user re-starts the app, my onCreate() gets called again and I get sendData() invoked twice a second. It goes on like that. Every time user comes out and starts again, one more sendData() per second happens.

What am I doing wrong? Is it my new Handler() creating problem? What is the best way to handle this? I want one sendData() call per second until user quits the app (form application manager).

score 105 · Answer 1 · answered Dec 26 '13 at 11:51

final Handler handler = new Handler();
    handler.postDelayed(new Runnable() {
      @Override
      public void run() {
        //Do something after 100ms
        Toast.makeText(c, "check", Toast.LENGTH_SHORT).show();  
        handler.postDelayed(this, 2000);
      }
    }, 1500);

score 31 · Answer 2 · answered Jun 01 '12 at 06:12

Perhaps involve the activity's life-cycle methods to achieve this:

Handler handler = new Handler();

@Override
protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      handler.post(sendData);
}

@Override
protected void onDestroy() {
      super.onDestroy();
      handler.removeCallbacks(sendData);
}


private final Runnable sendData = new Runnable(){
    public void run(){
        try {
            //prepare and send the data here..


            handler.postDelayed(this, 1000);    
        }
        catch (Exception e) {
            e.printStackTrace();
        }   
    }
};

In this approach, if you press back-key on your activity or call finish();, it will also stop the postDelayed callings.

Thank you for the point. In fact I wanted the postDelayed task to continue even when the user press back. Tried this code and it works as expected: postDelayed call stops when the user presses the back button. — zolio, Jun 29 '12 at 12:54

score 28 · Accepted Answer · edited May 29 '14 at 07:31

28

Why don't you create service and put logic in onCreate(). In this case even if you press back button service will keep on executing. and once you enter into application it will not call onCreate() again. Rather it will call onStart()

edited May 29 '14 at 07:31

naXa stands with Ukraine

35,493
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answered Jun 01 '12 at 06:11

Vipul

27,808
7
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Thank you. I created a service activity and it works well. I wanted the service task to continue running even when the back button is pressed. – zolio Jun 29 '12 at 12:52

Varun Chandran · Answer 4 · 2019-05-07T10:33:23.877

16

You can simplify the code like this.

In Java:

new Handler().postDelayed (() -> {
    //your code here
}, 1000);

In Kotlin:

Handler().postDelayed({
   //your code here
}, 1000)

edited May 07 '19 at 10:33

answered Sep 25 '17 at 08:47

Varun Chandran

647
9
23

score 2 · Answer 5 · answered Feb 11 '15 at 22:37

Please check the below its working on my side in below code your handler will run after every 1 Second when you are on same activity

 HandlerThread handlerThread = new HandlerThread("HandlerThread");
                handlerThread.start();
                handler = new Handler(handlerThread.getLooper());
                runnable = new Runnable()
                {
                    @Override
                    public void run()
                    {

                            handler.postDelayed(this, 1000);
                        }
                };
                handler.postDelayed(runnable, 1000);

score 1 · Answer 6 · answered Oct 26 '17 at 17:36

Handler h = new Handler() {
    @Override
    public void handleMessage(Message msg) {
        super.handleMessage(msg);
        if (msg.what==0){
            // do stuff
            h.removeMessages(0);  // clear the handler for those messages with what = 0
            h.sendEmptyMessageDelayed(0, 2000); 
        }
    }
};


 h.sendEmptyMessage(0);

score 0 · Answer 7 · answered Jun 01 '12 at 06:13

I think you could experiment with different activity flags, as it sounds like multiple instances.

"singleTop" "singleTask" "singleInstance"

Are the ones I would try, they can be defined inside the manifest.

http://developer.android.com/guide/topics/manifest/activity-element.html

score 0 · Answer 8 · answered Jun 01 '12 at 06:17

0

You should set andrid:allowRetainTaskState="true" to Launch Activity in Manifest.xml. If this Activty is not Launch Activity. you should set android:launchMode="singleTask" at this activity

answered Jun 01 '12 at 06:17

Folee

179
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Android - running a method periodically using postDelayed() call

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