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

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

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