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У меня есть MainActivity с FragmentContainerView, BottomNavigationView и FAB.

activity_main.xml:

 <?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.motion.widget.MotionLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@ id/motionLayoutActivityMain"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    app:layoutDescription="@xml/activity_main_scene"
    tools:context=".ui.MainActivity">


    <androidx.fragment.app.FragmentContainerView
        android:id="@ id/fragmentContainer"
        android:layout_width="0dp"
        android:layout_height="0dp"
        app:layout_constraintBottom_toTopOf="@ id/bottomNavigation"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent">

    </androidx.fragment.app.FragmentContainerView>

    <com.google.android.material.bottomnavigation.BottomNavigationView
        android:id="@ id/bottomNavigation"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:labelVisibilityMode="selected"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:menu="@menu/bottom_navigation_menu" />

    <androidx.constraintlayout.widget.Guideline
        android:id="@ id/verticalGuidelineActivityMain"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintGuide_percent="0.8" />

    <com.google.android.material.floatingactionbutton.FloatingActionButton
        android:id="@ id/filterFabActivityMain"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="16dp"
        android:layout_marginBottom="72dp"
        android:contentDescription="fab"
        android:src="@android:drawable/ic_menu_add"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toRightOf="@id/verticalGuidelineActivityMain" />

    <androidx.constraintlayout.widget.Guideline
        android:id="@ id/horizontalGuidelineActivityMain"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        app:layout_constraintGuide_percent="1"
        app:layout_constraintStart_toStartOf="parent" />

</androidx.constraintlayout.motion.widget.MotionLayout>
 

Когда я нажимаю на item1 или item2 BottomNavifationView, вызываемый fab.show(), если я нажимаю на item3, вызываемый fab.hide() .

MainActivity.kt:

 //SOME CODE BEFORE

binding.bottomNavigation.setOnNavigationItemSelectedListener { item ->
            when (item.itemId) {
                R.id.membersFragment -> {
                    fragmentManager.beginTransaction().hide(activeFragment).show(membersFragment).commit()
                    activeFragment = membersFragment

                    // Show fab when select membersFragment
                    binding.filterFabActivityMain.show()

                    true
                }
                R.id.teamsFragment -> {
                    fragmentManager.beginTransaction().hide(activeFragment).show(teamsFragment).commit()
                    activeFragment = teamsFragment

                    // Show fab when select teamsFragment
                    binding.filterFabActivityMain.show()

                    true
                }
                R.id.aboutFragment -> {
                    fragmentManager.beginTransaction().hide(activeFragment).show(aboutFragment).commit()
                    activeFragment = aboutFragment

                    // Hide fab when select aboutFragment
                    binding.filterFabActivityMain.hide()

                    true
                }
                else -> false
            }
        }

//SOME CODE AFTER
 

fab.hide() скрывает FAB, но если я нажму на позицию FAB, будет вызван fab.ClickListener.

fab.show() не будет показывать FAB.

MotionLayout управляет сценой, поэтому необходимо использовать app:visibilityMode="ignore" для ограничения FAB в сцене движения.

 <Constraint
android:id="@ id/filterFabActivityMain"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="16dp"
android:layout_marginBottom="72dp"
android:contentDescription="fab"
android:src="@android:drawable/ic_menu_add"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toRightOf="@id/verticalGuidelineActivityMain"
app:visibilityMode="ignore" />