[android] Android - running a method periodically using postDelayed() call

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).

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);

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);  

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

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);

You can simplify the code like this.

In Java:

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

In Kotlin:

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

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.

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