I have moved BottomNavigation codes from MainActivity to A class I have created for the BottomNaviction to make the code more organizing. When I moved the codes I got this error java.lang.RuntimeException: Unable to start activity ComponentInfo{com.moataz.mox/com.moataz.mox.ui.view.activity.MainActivity}: java.lang.IllegalStateException: FragmentManager has not been attached to a host. Short error message FragmentManager has not been attached to a host. And The error