https://www.angroid.gr/android-tutorials/%ce%b1%ce%bd%ce%b1%ce%b2%ce%b1%ce%b8%ce%bc%ce%af%cf%83%cf%84%ce%b5-%cf%83%ce%b5-android-4-1-2-jelly-bean-%cf%84%ce%bf-motorola-droid-razr