Android actionbar not visible

Principale extends ActionBarActivity should take care of the issue

Have you tried to set the app theme to a theme that supports the ActionBar, like Theme.Holo.Light?

Also, in your Activity you can try getActionBar().show();.

You have extended Activity. Try extending ActionBarActivity in java code

In my case, what fixed the issue, was the answer of this question; to remove

android:theme="@style/AppTheme"

from the tag in the Manifest.