Chap. 4: Why is handler needed with progress bar?

mprogers · December 21st, 2012, 01:46 PM

Hi, All:

In the code in chapter 4, on p. 175, the author keeps instantiating a new Runnable, everytime through the loop, to set the progress of the progress bar. Isn't that inefficient? i.e., why can't he just write:

progressStatus = doSomeWork();
progressBar.setProgress(progressStatus);

Instead of having to wrap the second line in a handler:

Code:

progressStatus = doSomeWork();
handler.post(new Runnable()
{     
     public void run(){
          progressBar.setProgress(progressStatus);
     }
});

Any insights would be appreciated.

Thanks,

Michael

BjÃ¶rnWagner · January 1st, 2013, 07:18 PM

The handler function is used for the android system to communicate between threads. Since the code starts the code in a second parallell executed thread it use the handler to transfer information back to the UI-thread.
The reason to have it in a second thread is that if an activity takes more than 5 seconds to execute in the main UI thread the Android system will stop the your activity will be killed and an error message will apair in the device window