【Android】BottomNavigationViewの使い方

BottomNavigationViewの使い方まとめ。

・参考動画

https://www.youtube.com/watch?v=JjfSjMs0ImQ

・公式ドキュメント

https://developer.android.com/reference/com/google/android/material/bottomnavigation/BottomNavigationView

・MainActivity

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        // 以下BottomNavigationViewの設定
        val navVie: BottomNavigationView = findViewById(R.id.bottom_navigation)
        val navController = findNavController(R.id.nav_host_fragment)
        val appBarConfiguration = AppBarConfiguration(setOf(
            R.id.navigation_first_fragment, R.id.navigation_second_fragment, R.id.navigation_third_fragment))
        setupActionBarWithNavController(navController, appBarConfiguration)
        navView.setupWithNavController(navController)
    }

}

・activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <com.google.android.material.bottomnavigation.BottomNavigationView
        android:id="@+id/bottom_navigation"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginStart="0dp"
        android:layout_marginEnd="0dp"
        android:background="?android:attr/windowBackground"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:menu="@menu_bottom_menu" />

    <fragment
        android:id="@+id/nav_host_fragment"
        android:name="androidx.navigation.fragment.NavHostFragment"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:defaultNavHost="true"
        app:layout_constraintBottom_toBottomOf="@id/nav_host_fragment"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:navGraph="@navigation/nav_graph" />

</androidx.constraintlayout.widget.ConstraintLayout>

※注意点 

<BottomNavigationView />

↓

<fragment />

の順にタグを書く

 ・nav_greph.xml(res/navigation/nav_graph.xml)

<?xml version="1.0" encoding="utf-8"?>
<navigation
    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/nav_graph"
    app:startDestination="@id/navigation_first_fragment">

    <fragment
        android:id="@+id/navigation_first_fragment"
        android:name="com.example.myapplicatoin.FirstFragment"
        android:label="first fragment"
        tools:layout="@layout/fragment_first" />

    <fragment
        android:id="@+id/navigation_second_fragment"
        android:name="com.example.myapplication.SecondFragment"
        android:label="second fragment"
        tools:layout="@layout/fragment_second" />

    <fragment
        android:id="@+id/navigation_third_fragment"
        android:name="com.example.myapplication.ThridFragment"
        android:label="thrid fragment"
        tools:layout="@layout/fragment_third" />

</navigation>

※注意点

<fragment>タグのidとbottom_menu.xmlで作成した<item>タグのを合わせる。

・bottom_menu.xml

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">
    <item
        android:id="@+id/navigation_first_fragment"
        android:icon="@drawable/ic_icon1"
        android:title="first fragment" />

    <item
        android:id="@+id/navigation_second_fragment"
        android:icon="@drawable/ic_icon2"
        android:title="second_fragment" />

    <item
        android:id="@+id/navigation_third_fragment"
        android:icon="@drawable/ic_icon3"
        android:title="third fragment" />

</menu>

 ※注意点

上記にも書いたが、<fragment>タグのidと<item>タグのを合わせる。

合わせることで、MainActivity.ktの設定で、画面遷移を行うことが出来る。