Develop Reference

ViewPager2 misses the tablayout indicator

The following problem occurred with me after migration from viewPager to viewPager2 - when I open my app, the tablyout indicator is missing by default. But if you make some swiping, the indicator will appears! Looks weird, because I made everything correct. There are my simplified Kotlin-code:
class ScheduleWeekFragment : ScheduleBaseFragment<ScheduleWeekViewModel>(ScheduleWeekViewModel::class) {
private val viewBinding by viewBinding(FragmentWeekBinding::bind)
private var titles: Array<String>? = null
// listeners
private val viewPagerListener = object : ViewPager2.OnPageChangeCallback() {
override fun onPageSelected(position: Int) {
viewModel.updateDayTitle(position)
}
}
// observers
private val selectedDayObserver = Observer<Int> {
viewBinding.viewPager2.currentItem = it
}
// lifecycle
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
titles = context?.resources?.getStringArray(R.array.schedule_fragment_day_abbreviations)
}
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? =
inflater.inflate(R.layout.fragment_week, container, false)
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
viewBinding.viewPager2.adapter = ScheduleViewPagerAdapter(this)
viewBinding.viewPager2.setPageTransformer(ZoomOutPageTransformer)
TabLayoutMediator(viewBinding.tabLayout, viewBinding.viewPager2) { tab, position ->
tab.text = titles?.getOrNull(position)
}.attach()
// observers
viewModel.viewPagerPosition.observe(viewLifecycleOwner, selectedDayObserver)
// listeners
viewBinding.viewPager2.registerOnPageChangeCallback(viewPagerListener)
}
override fun onDestroyView() {
viewBinding.viewPager2.unregisterOnPageChangeCallback(viewPagerListener)
super.onDestroyView()
}
}
And there is my simplified xml-code:
<?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:id="#+id/fragmentWeek"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#color/colorPrimary"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent">
<com.google.android.material.tabs.TabLayout
android:id="#+id/tabLayout"
style="#style/TabLayout1"
android:layout_width="match_parent"
android:layout_height="40dp"
android:verticalScrollbarPosition="left"
app:layout_constraintEnd_toEndOf="#+id/viewPager2"
app:layout_constraintStart_toStartOf="#+id/viewPager2"
app:layout_constraintTop_toBottomOf="#+id/scheduleToolbar"
app:tabGravity="start"
app:tabMode="scrollable"
android:background="#color/white"
tools:ignore="SpeakableTextPresentCheck" />
<androidx.viewpager2.widget.ViewPager2
android:id="#+id/viewPager2"
android:layout_width="0dp"
android:layout_height="0dp"
android:layout_alignParentStart="true"
android:layout_alignParentTop="true"
android:background="#color/white"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="#+id/tabLayout"
tools:ignore="SpeakableTextPresentCheck" />
</androidx.constraintlayout.widget.ConstraintLayout>

The problem was inside my observer:
private val selectedDayObserver = Observer<Int> {
// viewBinding.viewPager2.currentItem = it // wrong!
viewBinding.viewPager2.setCurrentItem(it, false) // correct!
}
I didn't find why in the official docs, but difference exists: the first variant works good with viewpager1, but for viewpager2, be careful and use the second complex variant.

ViewPager2 with Tablayout inside a fragment shows no swipe effect in kotlin

In my MainActivity I have a viewpager2 with Tablayout with 5 tabs. The swipe there is working fine. But in one of the 5 tabs I again have a viewpager2 with a tablayout of 3 tabs. In the inner viewpager2 (which is inside a fragment) the swipe isnt working at all and I don't understand why.
The outer viewpager2 is inside a activity while the inner viewpager2 is in the fragment
Viewpager2 inside fragment , swipe not working :
class FreelancerMyProjectsFragment : Fragment() {
lateinit var binding : FragmentFreelancerMyProjectsBinding
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
// Inflate the layout for this fragment
binding = DataBindingUtil.inflate(inflater,R.layout.fragment_freelancer_my_projects, container, false)
setUpViewPager()
addTabs()
return binding.root
}
private fun addTabs() {
TabLayoutMediator(binding.projectsTabLayout, binding.projectsViewPager) { tab, position ->
}.attach()
binding.projectsTabLayout.getTabAt(0)?.text =resources.getText(R.string.active)
binding.projectsTabLayout.getTabAt(1)?.text =resources.getText(R.string.bids)
binding.projectsTabLayout.getTabAt(2)?.text =resources.getText(R.string.past)
}
private fun setUpViewPager() {
val adapter = ScreenSlidePagerAdapterNewForFragment(this)
adapter.addFragment(ActiveProjectsFragment())
adapter.addFragment(BidsFragment())
adapter.addFragment(PastProjectFragment())
binding.projectsViewPager.offscreenPageLimit = 3
binding.projectsViewPager.adapter = adapter
}
}
class ScreenSlidePagerAdapterNewForFragment(fragment: Fragment) : FragmentStateAdapter(fragment) {
var fragmentList: ArrayList<Fragment> = ArrayList()
public fun addFragment(fragment: Fragment) {
fragmentList.add(fragment)
}
override fun getItemCount(): Int{ return fragmentList.size}
override fun createFragment(position: Int): Fragment {return fragmentList[position]}
}
And here is the layout:
<?xml version="1.0" encoding="utf-8"?>
<layout 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">
<androidx.constraintlayout.widget.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="match_parent">
<androidx.viewpager2.widget.ViewPager2
android:id="#+id/projectsViewPager"
android:layout_width="0dp"
android:layout_height="0dp"
app:layout_constraintTop_toBottomOf="#+id/projectsTabLayout"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent">
</androidx.viewpager2.widget.ViewPager2>
<com.google.android.material.tabs.TabLayout
android:id="#+id/projectsTabLayout"
android:layout_width="match_parent"
android:layout_height="60dp"
android:layout_marginHorizontal="40dp"
app:tabTextAppearance="#style/ProjectTabLayoutFreelancer"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent">
</com.google.android.material.tabs.TabLayout>
</androidx.constraintlayout.widget.ConstraintLayout>
</layout>
Please can someone tell me what I'm doing wrong?

The outer Viewpager is preventing the inner viewpager from receiving touch events. You need to intercept the event and stop the outer viewpager from swiping. See the link for implemented solution code

How to replace fragment inside ViewPager and change toolbar

I found an interesting feature in one of the applications, I want to repeat it. The application has ViewPager and TabLayout and a bunch of fragments inside.
On the first fragment there is a button img1
, by pressing it, the fragment is replaced by another img2
while ads_banner is removed and the toolbar is replaced,
and when swiping to the right and back, it shows fragment1, please tell me how this can be done. Here is what I already wrote:
MainActivity
class MainActivity : AppCompatActivity() {
private var mAdView: AdView? = null
#SuppressLint("ResourceType")
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
val adRequest = AdRequest.Builder().build()
mAdView = findViewById(R.id.adView)
mAdView!!.loadAd(adRequest)
initTab()
}
fun initTab() {
tab_layout.addTab(tab_layout.newTab().setIcon(R.drawable.image1)
tab_layout.addTab(tab_layout.newTab().setIcon(R.drawable.image2)
tab_layout.addTab(tab_layout.newTab().setIcon(R.drawable.image3)
tab_layout.tabGravity = TabLayout.GRAVITY_FILL
val adapter = MyPagerAdapter(supportFragmentManager, tab_layout.tabCount)
pager.adapter = adapter
pager.offscreenPageLimit = 2
pager.addOnPageChangeListener(TabLayout.TabLayoutOnPageChangeListener(tab_layout))
tab_layout.addOnTabSelectedListener(object : TabLayout.OnTabSelectedListener {
override fun onTabSelected(tab: TabLayout.Tab) {
pager.currentItem = tab.position
if (tab.position == 0) {
tab_layout.getTabAt(0)!!.setIcon(R.drawable.image1_focus)
}
if (tab.position == 1) {
tab_layout.getTabAt(1)!!.setIcon(R.drawable.image2_focus)
}
if (tab.position == 2) {
tab_layout.getTabAt(2)!!.setIcon(R.drawable.image3_focus)
}
}
override fun onTabUnselected(tab: TabLayout.Tab) {
if (tab.position == 0) tab_layout.getTabAt(0)!!.setIcon(R.drawable.image1)
if (tab.position == 1) tab_layout.getTabAt(1)!!.setIcon(R.drawable.image2)
if (tab.position == 2) tab_layout.getTabAt(2)!!.setIcon(R.drawable.image3)
}
override fun onTabReselected(tab: TabLayout.Tab) {
}
})
}
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"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/mainlayout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#color/white"
android:fitsSystemWindows="true"
android:orientation="vertical"
tools:context=".MainActivity">
<com.google.android.gms.ads.AdView
android:id="#+id/adView"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:background="#color/transparent"
app:adSize="SMART_BANNER"
app:adUnitId="#string/banner_key"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<androidx.appcompat.widget.Toolbar
android:id="#+id/toolbar"
style="#style/MyToolbar"
android:layout_width="match_parent"
android:layout_height="35dp"
android:layout_marginTop="2dp"
android:gravity="center"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="#id/adView"
app:popupTheme="#style/AppTheme.PopupOverlay">
<TextView
android:id="#+id/toolbar_txt"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:fontFamily="#font/sf_pro_display_regular"
android:textColor="#color/black"
android:textSize="24sp"
tools:layout_editor_absoluteX="206dp"
tools:layout_editor_absoluteY="7dp" />
</androidx.appcompat.widget.Toolbar>
<androidx.viewpager.widget.ViewPager
android:id="#+id/pager"
android:layout_width="match_parent"
android:layout_height="0dp"
app:layout_constraintBottom_toTopOf="#+id/tab_layout"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="#+id/toolbar" />
<com.google.android.material.tabs.TabLayout
android:id="#+id/tab_layout"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_gravity="bottom"
android:background="#fff"
android:elevation="6dp"
android:minHeight="?attr/actionBarSize"
android:theme="#style/ThemeOverlay.AppCompat.Dark.ActionBar"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:tabBackground="#drawable/tab_color_selector"
app:tabIndicatorColor="#2196F3"
app:tabIndicatorGravity="top"
app:tabIndicatorHeight="4dp" />
</androidx.constraintlayout.widget.ConstraintLayout>
MyPagerAdapter
class MyPagerAdapter(fm: FragmentManager, internal var mNumOfTabs: Int) : FragmentStatePagerAdapter(fm) {
override fun getItem(position: Int): Fragment {
when (position) {
0 -> {
return RootFragment()
// return Fragment1()
}
1 -> {
return Fragment2()
}
2 -> {
return Fragment3()
}
}
}
override fun getCount(): Int {
return mNumOfTabs
}
}
Fragment1
class Fragment1: Fragment() {
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
val view = inflater.inflate(R.layout.fragment_1, container, false)
return view
}
override fun onActivityCreated(savedInstanceState: Bundle?) {
super.onActivityCreated(savedInstanceState)
btnfr1.setOnClickListener {
val trans = fragmentManager!!.beginTransaction()
trans.replace(R.id.root_frame, Fragment4())
trans.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN)
trans.addToBackStack(null)
trans.commit()
}
}
RootFragment
class RootFragment : Fragment() {
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
val view = inflater.inflate(R.layout.root_fragment, container, false)
val transaction = fragmentManager!!.beginTransaction()
transaction.replace(R.id.root_frame, Fragment1())
transaction.commit()
return view
}
}
root_fragment.xml
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="#+id/root_frame" >
</FrameLayout>
In Fragment1, only the button for calling Fragment4. Tried to do as here https://www.codexpedia.com/android/android-viewpager-fragment-swap/
it turned out to replace Fragment1 with Fragment4, but I don’t know how to reset Fragment4 when swiping and don’t understand how to replace Toolbar and remove ads.

The trick is that as RootFragment is the fragment on the 0th index, what you need to do is show the original fragment as a child fragment of RootFragment using fragment transactions via childFragmentManager.
This way, you can replace the children of RootFragment, without actually having to replace RootFragment itself inside the ViewPager.

You need to implement createFragment and getItemCount methods in MyPagerAdapter to supply instances of fragments as pages to ViewPager.
Modify MyPagerAdapter class as shown below and test:
class MyPagerAdapter(fm: FragmentManager, internal var mNumOfTabs: Int) : FragmentStatePagerAdapter(fm) {
override fun getItemCount(): Int = mNumOfTabs
override fun createFragment(position: Int): Fragment {
when (position) {
0 -> {
return RootFragment()
}
1 -> {
return Fragment2()
}
2 -> {
return Fragment3()
}
}
}
}

Viewpager inside BottomsheetdialogFragment not showing Fragment

I have implemented BottomSheetDialogFragment into OptionsFragment.In which I have added viewpager so I can do swipe animation for SignInSignUpOptionsFragment which I want to add in viewpager and button to Swipe SignInSignUpOptionsFragment with different option. SignInSignUpOptionsFragment has options of Login(+ social accounts).
AccountFragment
login_btn.onClickListener( v -> {
OptionsFragment optionsFragment = new OptionsFragment(true);
optionsFragment.show(getChildFragmentManager(), "Login");
});
OptionsFragment
class OptionsFragment(private val isLogin: Boolean) : BottomSheetDialogFragment() {
private var fragmentView: View? = null
lateinit var viewPager: ViewPager
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
fragmentView = inflater.inflate(R.layout.signup_popover, container, false)
val pagerAdapter = MyPagerAdapter(childFragmentManager)
viewPager = fragmentView!!.findViewById(R.id.vpPager)
viewPager.adapter = pagerAdapter
viewPager.currentItem = 0
return fragmentView
}
}
class MyPagerAdapter(fragmentManager: FragmentManager?) : FragmentStatePagerAdapter(fragmentManager!!, BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT) {
// Returns total number of pages
override fun getCount(): Int {
return NUM_ITEMS
}
// Returns the fragment to display for that page
override fun getItem(position: Int): Fragment {
return when(position) {
0 -> SignInSignUpOptionsFragment.newInstance(true)
1 -> SignInSignUpOptionsFragment.newInstance(false)
else -> null!!
}
}
// Returns the page title for the top indicator
override fun getPageTitle(position: Int): CharSequence? {
return "Page $position"
}
companion object {
private const val NUM_ITEMS = 2
}
here's my layout file
<androidx.constraintlayout.widget.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#color/utilityGrey2">
<androidx.viewpager.widget.ViewPager
android:id="#+id/vpPager"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="parent" />
<LinearLayout
android:id="#+id/login_no_account_group"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginBottom="24dp"
android:layout_marginLeft="21dp"
android:layout_marginRight="21dp"
android:layout_marginTop="52dp"
android:orientation="vertical"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="#id/vpPager">
<androidx.appcompat.widget.AppCompatTextView
android:id="#+id/switch_sign_up_description"
style="#style/HelpText"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:text="#string/no_account" />
<androidx.appcompat.widget.AppCompatTextView
android:id="#+id/switch_sign_up"
style="#style/HelpText"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center_horizontal"
android:text="#string/sign_up_caps" />
</LinearLayout>
but I am not able to see any fragment inside ViewPager. Only bottom "login_no_account_group" is displaying as Bottomsheet. I don't want to use TabLayout, instead I want to change page on switch_sign_up click
viewPager.currentItem = 1
Is it possible ? any other alternative welcome as well

RecyclerView not showing in Layout

I want to achieve a layout as shown in the Android Studio preview (left). However if executed in the emulator, only the button is visible and the RecyclerView is not visible/populated (right).
The XML code:
<?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"
style="#style/AppTheme">
<androidx.recyclerview.widget.RecyclerView
android:id="#+id/list"
android:name="com.example.app.ItemFragment"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_marginLeft="16dp"
android:layout_marginRight="16dp"
app:layoutManager="LinearLayoutManager"
tools:context=".ItemFragment"
tools:listitem="#layout/fragment_item"
android:scrollbars="vertical"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<com.google.android.material.floatingactionbutton.FloatingActionButton
android:id="#+id/floatingActionButton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="bottom|center_horizontal"
android:layout_margin="#dimen/fab_margin"
android:clickable="true"
android:focusable="true"
android:src="#android:drawable/ic_input_add"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>
However if the RecyclerView is alone in the fragment the list is populated (but of course the action button is not showing). Code see below. And yes, my list which should be shown is not empty.
<?xml version="1.0" encoding="utf-8"?>
<androidx.recyclerview.widget.RecyclerView 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/list"
android:name="com.example.app.ItemFragment"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_marginLeft="16dp"
android:layout_marginRight="16dp"
app:layoutManager="LinearLayoutManager"
tools:context=".ItemFragment"
tools:listitem="#layout/fragment_item" >
</androidx.recyclerview.widget.RecyclerView>
I have already tried using RelativeLayout and FrameLayout, but I still get the same result. The same behavior occurs if I use e.g. a TextView instead of the action button.
--- Requested additional info ---
Adapter class (automatically generated by Android Studio, template):
class MyItemRecyclerViewAdapter(
private val mValues: List<DummyItem>,
private val mListener: OnListFragmentInteractionListener?
) : RecyclerView.Adapter<MyItemRecyclerViewAdapter.ViewHolder>() {
private val mOnClickListener: View.OnClickListener
init {
mOnClickListener = View.OnClickListener { v ->
val item = v.tag as DummyItem
// Notify the active callbacks interface (the activity, if the fragment is attached to
// one) that an item has been selected.
mListener?.onListFragmentInteraction(item)
}
}
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
val view = LayoutInflater.from(parent.context)
.inflate(R.layout.fragment_item, parent, false)
return ViewHolder(view)
}
override fun onBindViewHolder(holder: ViewHolder, position: Int) {
val item = mValues[position]
holder.mIdView.text = item.id
holder.mContentView.text = item.content
with(holder.mView) {
tag = item
setOnClickListener(mOnClickListener)
}
}
override fun getItemCount(): Int = mValues.size
inner class ViewHolder(val mView: View) : RecyclerView.ViewHolder(mView) {
val mIdView: TextView = mView.item_number
val mContentView: TextView = mView.content
override fun toString(): String {
return super.toString() + " '" + mContentView.text + "'"
}
}
}
List fragment (automatically generated by Android Studio, template):
class ItemFragment : Fragment() {
// TODO: Customize parameters
private var columnCount = 1
private var listener: OnListFragmentInteractionListener? = null
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
arguments?.let {
columnCount = it.getInt(ARG_COLUMN_COUNT)
}
}
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
val view = inflater.inflate(R.layout.fragment_item_list, container, false)
// Set the adapter
if (view is RecyclerView) {
with(view) {
layoutManager = when {
columnCount <= 1 -> LinearLayoutManager(context)
else -> GridLayoutManager(context, columnCount)
}
adapter = MyItemRecyclerViewAdapter(DummyContent.ITEMS, listener)
}
}
return view
}
override fun onAttach(context: Context) {
super.onAttach(context)
if (context is OnListFragmentInteractionListener) {
listener = context
} else {
throw RuntimeException(context.toString() + " must implement OnListFragmentInteractionListener")
}
}
override fun onDetach() {
super.onDetach()
listener = null
}
/**
* This interface must be implemented by activities that contain this
* fragment to allow an interaction in this fragment to be communicated
* to the activity and potentially other fragments contained in that
* activity.
*
*
* See the Android Training lesson
* [Communicating with Other Fragments](http://developer.android.com/training/basics/fragments/communicating.html)
* for more information.
*/
interface OnListFragmentInteractionListener {
// TODO: Update argument type and name
fun onListFragmentInteraction(item: DummyItem?)
}
companion object {
// TODO: Customize parameter argument names
const val ARG_COLUMN_COUNT = "column-count"
// TODO: Customize parameter initialization
#JvmStatic
fun newInstance(columnCount: Int) =
ItemFragment().apply {
arguments = Bundle().apply {
putInt(ARG_COLUMN_COUNT, columnCount)
}
}
}
}

Try this for your layout
<?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"
style="#style/AppTheme"
android:layout_width="match_parent"
android:layout_height="match_parent">
<androidx.recyclerview.widget.RecyclerView
android:id="#+id/list"
android:name="com.example.app.ItemFragment"
android:layout_width="0dp"
android:layout_height="0dp"
android:scrollbars="vertical"
app:layoutManager="LinearLayoutManager"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
tools:context=".ItemFragment"
tools:listitem="#layout/fragment_item" />
<com.google.android.material.floatingactionbutton.FloatingActionButton
android:id="#+id/floatingActionButton"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="bottom|center_horizontal"
android:layout_margin="#dimen/fab_margin"
android:clickable="true"
android:focusable="true"
android:src="#android:drawable/ic_input_add"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>
Inside ItemFragment.kt replace onCreateView with
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
return inflater.inflate(R.layout.fragment_item_list, container, false)
}
After that go ahead and implement onViewCreated as such
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
with(list) {
layoutManager = when {
columnCount <= 1 -> LinearLayoutManager(requireContext())
else -> GridLayoutManager(requireContext(), columnCount)
}
adapter = MyItemRecyclerViewAdapter(DummyContent.ITEMS)
}
}
This should fix your problem because the AS template is assuming that the rootview will be a RecyclerView and is treating the whole layout as such.