I'm wondering when should I use handler.post(runnable);
and when should I use
new Thread(runnable).start();
It is mentioned in developers documentation for Handler:
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 I write in the onCreate()
of Activity
class:
Handler handler = new Handler();
handler.post(runnable);
then runnable will be called in a separate thread or in the Activity's thread?
You should use Handler.post()
whenever you want to do operations on the UI thread.
So let's say you want to change a TextView
's text in the callback. Because the callback is not running on the UI thread, you should use Handler.post()
.
In Android, as in many other UI frameworks, UI elements (widgets) can be only modified from UI thread.
Also note that the terms "UI thread" and "main thread" are often used interchangeably.
Edit: an example of the long-running task:
mHandler = new Handler();
new Thread(new Runnable() {
@Override
public void run () {
// Perform long-running task here
// (like audio buffering).
// You may want to update a progress
// bar every second, so use a handler:
mHandler.post(new Runnable() {
@Override
public void run () {
// make operation on the UI - for example
// on a progress bar.
}
});
}
}).start();
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.