activity_main.xml

<FrameLayout                                                                                        
    xmlns:android="http://schemas.android.com/apk/res/android"                                       
    xmlns:tools="http://schemas.android.com/tools"                                                   
    android:id="@+id/fragment"                                                                       
    android:name="whatever.here.MainFragment"                                          
    android:layout_width="match_parent"                                                             
    android:layout_height="match_parent"                                                            
    tools:layout="@layout/fragment_main"                                                            
    />