https://stackoverflow.com/questions/53864534/how-to-combine-bottomappbar-fab-with-bottomnavigationview

https://www.geeksforgeeks.org/how-to-add-a-floating-action-button-to-bottom-navigation-bar-in-android/

cradle margin 과 cradle radius

https://www.geeksforgeeks.org/theming-floating-action-button-with-bottom-navigation-bar-in-android/

<Constraint>

<FragmentContainer> </>

<Coordinate>

<Bottom Bar> </>

<FAB/>

<Constratin>

1안

<?xml version="1.0"encoding="utf-8"?>
<layoutxmlns:android="<http://schemas.android.com/apk/res/android>"
xmlns:app="<http://schemas.android.com/apk/res-auto>"
xmlns:tools="<http://schemas.android.com/tools>">

    <data>

    </data>

    <androidx.constraintlayout.widget.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="match_parent">

        <androidx.fragment.app.FragmentContainerView
android:id="@+id/nav_container"
android:name="androidx.navigation.fragment.NavHostFragment"
android:layout_width="match_parent"
android:layout_height="0dp"
app:defaultNavHost="true"
android:layout_marginBottom="50dp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
app:navGraph="@navigation/bottom_nav_graph" />
<!--여기 MarginBottom같은 경우에는 추후 결정된 BottomAppbar height 만큼 적용해줄것-->

<androidx.coordinatorlayout.widget.CoordinatorLayout
android:id="@+id/cd_home"
android:layout_width="match_parent"
android:layout_height="90dp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent">

            <com.google.android.material.bottomappbar.BottomAppBar
android:id="@+id/bottom_bar_home"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_gravity="bottom"
app:backgroundTint="?attr/colorPrimary"
app:fabCradleMargin="10dp"
app:fabCradleRoundedCornerRadius="10dp"
app:fabCradleVerticalOffset="10dp"
app:contentInsetEnd="0dp"
app:contentInsetStart="0dp"
app:fabAlignmentMode="center"
app:fabAnchorMode="cradle">

                <com.google.android.material.bottomnavigation.BottomNavigationView
android:id="@+id/bottom_nav_home"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:backgroundTint="@android:color/transparent"
app:elevation="0dp"
app:itemIconTint="@android:color/white"
app:itemRippleColor="@android:color/white"
app:itemTextColor="@android:color/white"
app:menu="@menu/bottom_nav_menu" />
            </com.google.android.material.bottomappbar.BottomAppBar>

            <com.google.android.material.floatingactionbutton.FloatingActionButton
android:id="@+id/fab_home"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:src="@drawable/ic_add"
app:layout_anchor="@id/bottom_bar_home" />

        </androidx.coordinatorlayout.widget.CoordinatorLayout>

    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>