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copied!<p>What happens if the user presses BACK or HOME after entering in the "data of a 'problem'", before the "solution" is ready?</p> <p>If the answer is that you do not need to do anything, then get rid of the <code>Service</code>, and have the <code>Activity</code> do the work to compute the solution (perhaps using an <code>AsyncTask</code>). You are not gaining anything in this case by using a <code>Service</code>.</p> <p>If, however, the user will still want the "solution", then using a <code>Service</code> is fine, but you have to take into account that the <code>Activity</code> that started the service may no longer exist or may not be in the foreground.</p> <p>One way to handle this is to use an ordered broadcast. Have the <code>Activity</code> register a high-priority <code>BroadcastReceiver</code> for the broadcast when it is in the foreground (via <code>onResume()</code> and <code>onPause()</code>), and register a low-priority <code>BroadcastReceiver</code> for the same broadcast via the manifest. The <code>Service</code> would <code>sendOrderedBroadcast()</code> when its work is complete. The <code>Activity</code>-registered <code>BroadcastReceiver</code> would update its UI with the result and abort the broadcast. The manifest-registered <code>BroadcastReceiver</code> would raise a <code>Notification</code> to let the user know about the completed work. <a href="http://commonsware.com/blog/2010/08/11/activity-notification-ordered-broadcast.html" rel="nofollow">Here is a blog post</a> with more about this pattern, and <a href="https://github.com/commonsguy/cw-advandroid/tree/master/Broadcast/Ordered" rel="nofollow">here is a sample project</a> that demonstrates its use.</p>

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