reiley reiley - 2 months ago 16
Android Question

When to use & when to new Thread()

I'm wondering when to use
& when to use
new Thread(runnable).start();

It is mentioned in developers doc:

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.

Does this mean if in the
class I write:

Handler handler = new Handler();

then, runnable will be called in a seperate thread or on the Activity's thread?

Thank You


You should use whenever you want to do operations in the UI thread.

So let's say in the callback (which is running in separate thread) you want to change a TextView's text, you should use

In Android, as in many other UI frameworks, UI elements (widgets) can be only modified from main thread.

Edit: the example of long-running tasks

mHandler = new Handler();

new Thread(new Runnable() {
  public void run () {
    // Perform long-running task here
    // (like audio buffering).
    // you may want to update some progress
    // bar every second, so use handler: Runnable() {
     public void run () {
       // make operation on UI - on example
       // on progress bar.

Of course, if the task you want to perform is really long and there is a risk that user might switch to some another app in the meantime, you should consider using a Service.