There are a few times when the user presses the back button on my app, and unfortunately he doesn't get out; the activity slides, but behind it there is exactly the same one...How is that possible? How could I avoid it? should I implementate something for the onBackPressed() method? Thanks for your advices.
You don't have to do implement onBackPressed. This sounds like multiple instances of the activity are being created/started, which is expected default behaviour when calling .startActivity() Check out the docs Tasks and Back Stack.
You could use singleTop as the launchmode or set the Intent.FLAG_ACTIVITY_SINGLE_TOP
on the intent that launches the activity.
Intent detailsIntent = new Intent(mContext, DetailsActivity.class);
detailsIntent.setFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP)
startActivity(detailsIntent);