How to run a Runnable thread in Android at defined intervals?

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?

Solution 1:

The simple fix to your example is :

handler = new Handler();

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

handler.postDelayed(r, 1000);

Or we can use normal thread for example (with original Runner) :

Thread thread = new Thread() {
    @Override
    public void run() {
        try {
            while(true) {
                sleep(1000);
                handler.post(this);
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
};

thread.start();

You may consider your runnable object just as a command that can be sent to the message queue for execution, and handler as just a helper object used to send that command.

More details are here http://developer.android.com/reference/android/os/Handler.html

Solution 2:

new Handler().postDelayed(new Runnable() {
    public void run() {
        // do something...              
    }
}, 100);

Solution 3:

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");
}

Solution 4:

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

new Thread(runnable).start();//to work in Background

Solution 5:

I believe for this typical case, i.e. to run something with a fixed interval, Timer is more appropriate. Here is a simple example:

myTimer = new Timer();
myTimer.schedule(new TimerTask() {          
@Override
public void run() {
    // If you want to modify a view in your Activity
    MyActivity.this.runOnUiThread(new Runnable()
        public void run(){
            tv.append("Hello World");
        });
    }
}, 1000, 1000); // initial delay 1 second, interval 1 second

Using Timer has few advantages:

Initial delay and the interval can be easily specified in the schedule function arguments
The timer can be stopped by simply calling myTimer.cancel()
If you want to have only one thread running, remember to call myTimer.cancel() before scheduling a new one (if myTimer is not null)