ViewPager2を利用したサンプルコードを書いた

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AndroidStudioのNew ProjectでTabbed Activityを選択したら
ViewPager2でなくViewPagerのサンプルが出来上がった

いや、いや、ViewPager2にしてくださいよ
と思いサンプルコードを書いてみた

・MainActivity

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        val sectionsPagerAdapter = SectionsPagerAdapter(this)
        view_pager.adapter = sectionsPagerAdapter

        TabLayoutMediator(tabs, view_pager) { tab, position ->
            tab.text = "TAB ${(position + 1)}"
        }.attach()
    }
}

・activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.coordinatorlayout.widget.CoordinatorLayout 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:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <androidx.viewpager2.widget.ViewPager2
        android:id="@+id/view_pager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_behavior="@string/appbar_scrolling_view_behavior" />

    <com.google.android.material.appbar.AppBarLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:theme="@style/AppTheme.AppBarOverlay">

        <androidx.appcompat.widget.Toolbar
            android:layout_width="match_parent"
            android:layout_height="?actionBarSize"
            app:title="@string/app_name" />

        <com.google.android.material.tabs.TabLayout
            android:id="@+id/tabs"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:background="?attr/colorPrimary" />
    </com.google.android.material.appbar.AppBarLayout>


</androidx.coordinatorlayout.widget.CoordinatorLayout>

・SectionsPagerAdapter

class SectionsPagerAdapter(fm: FragmentActivity)
    : FragmentStateAdapter(fm) {

    override fun createFragment(position: Int): Fragment = PlaceholderFragment.newInstance(position + 1)

    override fun getItemCount(): Int {
        return 2
    }
}

・PlaceholderFragment

class PlaceholderFragment : Fragment() {

    override fun onCreateView(
            inflater: LayoutInflater, container: ViewGroup?,
            savedInstanceState: Bundle?
    ): View? {
        val root = inflater.inflate(R.layout.fragment_main, container, false)
        val textView: TextView = root.findViewById(R.id.section_label)
        textView.text = arguments?.getInt(ARG_SECTION_NUMBER, 0).toString()
        return root
    }

    companion object {
        private const val ARG_SECTION_NUMBER = "section_number"

        fun newInstance(sectionNumber: Int): PlaceholderFragment {
            return PlaceholderFragment().apply {
                arguments = Bundle().apply {
                    putInt(ARG_SECTION_NUMBER, sectionNumber)
                }
            }
        }
    }
}

・fragment_main.xml

<androidx.constraintlayout.widget.ConstraintLayout 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/constraintLayout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".ui.main.PlaceholderFragment">

    <TextView
        android:id="@+id/section_label"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:gravity="center"
        android:textSize="36sp"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:text="1" />

</androidx.constraintlayout.widget.ConstraintLayout>

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