スライドするフラグメント

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アクティビティにページャーを作成する。

<?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"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <androidx.viewpager2.widget.ViewPager2
        xmlns:android="http://schemas.android.com/apk/res/android"
        android:id="@+id/pager"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

フラグメントを二つ作って、activityを次のように書き換える。

package com.konishisoft.pagertest

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.transition.Slide
import android.util.Log
import android.view.Gravity
import android.widget.Button
import androidx.fragment.app.Fragment
import androidx.fragment.app.FragmentActivity
import androidx.fragment.app.FragmentManager
import androidx.viewpager2.adapter.FragmentStateAdapter
import androidx.viewpager2.widget.ViewPager2

private const val NUM_PAGES = 2

class MainActivity : AppCompatActivity() {
    private lateinit var viewPager: ViewPager2

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

        viewPager = findViewById(R.id.pager)

        val pagerAdapter = ScreenSlidePagerAdapter(this)
        viewPager.adapter = pagerAdapter
    }

    override fun onBackPressed() {
        if (viewPager.currentItem == 0) {
            // If the user is currently looking at the first step, allow the system to handle the
            // Back button. This calls finish() on this activity and pops the back stack.
            super.onBackPressed()
        } else {
            // Otherwise, select the previous step.
            viewPager.currentItem = viewPager.currentItem - 1
        }
    }

    private inner class ScreenSlidePagerAdapter(fa: FragmentActivity) : FragmentStateAdapter(fa) {
        override fun getItemCount(): Int = NUM_PAGES

        override fun createFragment(position: Int): Fragment {
            if(position == 0) {
                return BlankFragment()
            }
            else {
                return BlankFragment2()
            }
        }
    }
}

かなり簡単。