How to run a Runnable thread in Android at defined

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?

Answer 1

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");
}

Answer 2

Handler handler=new Handler();
Runnable r = new Runnable(){
    public void run() {
        tv.append("Hello World");                       
        handler.postDelayed(r, 1000);
    }
}; 
handler.post(r);

Answer 3

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 

Answer 4

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.