Update UI from running thread

Question

I want to write a download manager app, in the activity I add a progress bar which show the current progress to the user, now if user touch the back button and re-open the activity again this ProgressBar won't be updated.

To avoid from this problem I create a single thread with unique name for each download that keep progress runnable and check if that thread is running in onResume function, if it is then clone it to the current thread and re-run the new thread again but it won't update my UI either, Any ideas !?

@Override
public void onResume() 
{
    super.onResume();
    Set<Thread> threadSet = Thread.getAllStackTraces().keySet();
    Thread[] threadArray = threadSet.toArray(new Thread[threadSet.size()]);
    for (int i = 0; i < threadArray.length; i++)
        if (threadArray[i].getName().equals(APPLICATION_ID))
        {
            mBackground = new Thread(threadArray[i]);
            mBackground.start();
            downloadProgressBar.setVisibility(View.VISIBLE);
            Toast.makeText(showcaseActivity.this
                    , "Find that thread - okay", Toast.LENGTH_LONG).show();
        }
}

private void updateProgressBar()
{
    Runnable runnable = new updateProgress();
    mBackground  = new Thread(runnable);
    mBackground.setName(APPLICATION_ID);
    mBackground.start();
}

private class updateProgress implements Runnable
{
    public void run() 
    {
        while (Thread.currentThread() == mBackground)
            try 
            {
                Thread.sleep(1000); 
                Message setMessage = new Message();
                setMessage.what = mDownloadReceiver.getProgressPercentage();        
                mHandler.sendMessage(setMessage);
            }
            catch (InterruptedException e) 
            {
                Thread.currentThread().interrupt();
            } 
            catch (Exception e) 
            {/* Do Nothing */}
    }
}

private Handler mHandler = new Handler()
{
    @Override
    public void handleMessage(Message getMessage) 
    {
        downloadProgressBar.setIndeterminate(false);
        downloadProgressBar.setProgress(getMessage.what);
        if (getMessage.what == 100)
            downloadProgressBar.setVisibility(View.GONE);
    }
};

Download button code:

downloadBtn.setOnClickListener(new View.OnClickListener()
{
    @Override
    public void onClick(View arg0) 
    {
        downloadProgressBar.setVisibility(View.VISIBLE);
        downloadProgressBar.setIndeterminate(true);
        downloadProgressBar.setMax(100);    
        Intent intent = new Intent(showcaseActivity.this, downloadManagers.class);
        intent.putExtra("url", "http://test.com/t.zip");
        intent.putExtra("receiver", mDownloadReceiver);
        startService(intent);
        updateProgressBar();
    }
});

Answer 1

I'd strongly recommend reading the Android Developer blog post on Painless Threading. As it states, the easiest way to update your UI from another thread is using Activity.runOnUiThread.