Question

My activity have a ProgressBar. When start activity, I’ll check value get from another place and update to ProgressBar. Here’s my code:

final ProgressBar progressBar = (ProgressBar) findViewById(R.id.progressBar_detail);
final TextView progressText = (TextView) findViewById(R.id.progressText_detail);
final ImageView btnCancel = (ImageView) findViewById(R.id.imgCancel_detail);
progressBar.setVisibility(View.VISIBLE);
progressText.setVisibility(View.VISIBLE);
btnCancel.setVisibility(View.VISIBLE);
Thread t = new Thread() {
    public void run() {
        ((Activity) ctx).runOnUiThread(new Runnable() {
            public void run() {
                int oldProgress = 0;
                while (progressBar.getProgress() < 100) {
                    int value = Downloader.progress.get(gameId+ "");
                    if (value != oldProgress) {
                        oldProgress = value;
                        progressBar.setProgress(value);
                        progressText.setText(value + " %");
                    }
                }
            }
        });
    }
};
t.start();

Value of ProgressBar i get from int value = Downloader.progress.get(gameId) and it’s correct. But when I run this code, the activity is not responding and not showing anything (but app not crash). Seems like the thread to update ProgressBar running and block the UI thread so the activity layout is not showing.

What’s wrong with my code? What is the correct way to update ProgressBar in this situation?

Answer 1

You are running a while (progressBar.getProgress() < 100) in the UI thread (you use runOnUiThread) so UI thread will be blocked (and nothing painted) until this loop finish.

You can:

• Put the runOnUiThread inside the loop and, maybe, a sleep inside de runOnUiThread call. However, it is not the preferred kind of solution since you are using too much CPU to just look for a value change. The sleep approach it a bit ugly but solves the cpu problem. It would be something like::

  Thread t = new Thread() {
      public void run() {
      int oldProgress = 0;
  
      while (progressBar.getProgress() < 100) {
              ((Activity) ctx).runOnUiThread(new Runnable() {
                  public void run() {
                      int value = Downloader.progress.get(gameId+ "");
                      if (value != oldProgress) {
                          oldProgress = value;
                          progressBar.setProgress(value);
                          progressText.setText(value + " %");
                      }
                  }
              }
              Thread.sleep(500);
          }
      });
    }
  };
  

• Update the progress bar in an event way so you only call (in the UI thread) the update code when progress changes. It is the preferred way.