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Fragments ❤ ViewPager2


The ViewPager2 is a pretty nice rework of the ViewPager API. Some new features you may find with the ViewPager2 are:

1- Vertical scrolling. You can simply enable it by adding: android:orientation="vertical" in the <ViewPager2> tag in your xml file.
2- Right to left support: you can set the android:layoutDirection="rtl" to enable this.
3- Support for DiffUtil, because it is based on RecyclerView.
4 - Fragments improved support, which we will talk about below.

So, let's suppose that we have 2 Fragments: HomeFragment and SchoolFragment. In the Activity/Fragment xml file, which is going to hold these two sliding by switching with each-other, place the ViewPager2 tag:

<androidx.viewpager2.widget.ViewPager2
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/my_view_pager"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >"
Now, let's set up code in the MainActivity (in my case this is the name of the Activity):

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.my_view_pager)
        val tabLayout = findViewById(R.id.tabs)
        val pagerAdapter = ScreenSlidePagerAdapter(this)
        viewPager.adapter = pagerAdapter
        TabLayoutMediator(tabLayout, viewPager) { tab, position ->
            when (position) {
                0 -> tab.text = "Home"
                1 -> tab.text = "School"
            }
        }.attach() //this replaces the tabLayout.setupWithViewPager() from ViewPager API
    }

    override fun onBackPressed() {
        if (viewPager.currentItem == 0) {
            super.onBackPressed() //if I'm in the first Fragment just go back
        } else {
            viewPager.currentItem = viewPager.currentItem - 1 //just slide to the first Fragment
        }
    }

    private inner class ScreenSlidePagerAdapter(fragmentActivity: FragmentActivity) : FragmentStateAdapter(fragmentActivity) {
        override fun getItemCount(): Int = 2 //because I have two Fragments

        override fun createFragment(position: Int): Fragment = if (position == 0) {
            HomeFragment()
        } else {
            SchoolFragment()
        }
    }
}
Some things to spot here though.

1- Notice that you have the FragmentStateAdapter instead of FragmentStatePagerAdapter.

2- To associate TabLayout with the ViewPager there is no more tabLayout.setupWithViewPager(). Instead you should import com.google.android.material:material:1.1.0-beta01 or later version of the dependency. And than you can do:

TabLayoutMediator(tabLayout, viewPager) { tab, position ->
            when (position) {
                0 -> tab.text = "Home"
                1 -> tab.text = "School"
            }
        }.attach()

And that's it, now you have your shiny new ViewPager2 set up with Fragments.

Helpful resources:
Slide between Fragments using Viewpager2.
Turning the Page: Migrating to ViewPager2 (Android Dev Summit '19).

Stavro Xhardha

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