TabLayout MVVM Kotlin

FirstFragment.kt

class FirstFragment : Fragment() {

    private var _binding: FragmentFirstBinding? = null
    private val binding get() = _binding!!

    val viewModel by activityViewModels<MyViewModel>()


    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View {

        _binding = FragmentFirstBinding.inflate(inflater, container, false)
        return binding.root

    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)

        initViewPager()


        viewModel.getCountList.observe(viewLifecycleOwner, Observer { sparseArray ->

            val size: Int = sparseArray.size()
            for (i in 0 until size) {
                val key: Int = sparseArray.keyAt(i)
                val value: Int = sparseArray.valueAt(i)
                Log.i("TAG", "key: $key value: $value")

                val title = when (key) {
                    0 -> "In: $value"
                    1 -> "Out: $value"
                    else -> "?"
                }
                changeTabTitle(key, title)

            }

        })

    }

    override fun onDestroyView() {
        super.onDestroyView()
        _binding = null
    }


    private fun initViewPager() {

        val pagerAdapter = CustomPagerAdapter(requireActivity())
        val oneFragment = ListOneFragment().apply {
            arguments = Bundle().apply {
                putInt(MyConstants.ARG_POSITION, 0)
            }
        }
        val twoFragment = ListTwoFragment().apply {
            arguments = Bundle().apply {
                putInt(MyConstants.ARG_POSITION, 1)
            }
        }

        pagerAdapter.addFragment(oneFragment, "In: 0")
        pagerAdapter.addFragment(twoFragment, "Out: 0")

        binding.viewPager.adapter = pagerAdapter

        TabLayoutMediator(binding.tabLayout, binding.viewPager) { tab, position ->
            tab.text = pagerAdapter.getPageTitle(position) //"${position + 1}"
        }.attach()

    }


    private fun changeTabTitle(position: Int, title: String) {
        val tabLayout = binding.tabLayout
        val tab0 = tabLayout.getTabAt(position)
        tab0?.text = title
    }

    private inner class CustomPagerAdapter(fa: FragmentActivity) : FragmentStateAdapter(fa) {
        private val mFragmentList = ArrayList<Fragment>()
        private val mFragmentTitleList = ArrayList<String>()

        override fun getItemCount(): Int {
            return mFragmentList.size
        }

        override fun createFragment(position: Int): Fragment {
            return mFragmentList[position]
        }

        fun getPageTitle(position: Int): CharSequence {
            return mFragmentTitleList[position]
        }

        fun addFragment(fragment: Fragment, title: String) {
            mFragmentList.add(fragment)
            mFragmentTitleList.add(title)
        }

    }
}

FragmentFirst.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:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".FirstFragment">

    <com.google.android.material.tabs.TabLayout
        android:id="@+id/tab_layout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:contentDescription="@string/second_fragment_label"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <androidx.viewpager2.widget.ViewPager2
        android:id="@+id/view_pager"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/tab_layout" />


</androidx.constraintlayout.widget.ConstraintLayout>

FragmentSecond.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:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".ListOneFragment">

    <TextView
        android:id="@+id/textview_second"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintBottom_toTopOf="@id/button_second"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/button_second"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/previous"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@id/textview_second" />
</androidx.constraintlayout.widget.ConstraintLayout>

ListOneFragment.kt

class ListOneFragment : Fragment() {

    companion object {
        private const val TAG = "ListOneFragment"
    }

    private var _binding: FragmentSecondBinding? = null
    private val binding get() = _binding!!

    val viewModel by activityViewModels<MyViewModel>()


    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View {
        _binding = FragmentSecondBinding.inflate(inflater, container, false)
        return binding.root
    }

    override fun onDestroyView() {
        super.onDestroyView()
        _binding = null
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)

        arguments?.takeIf { it.containsKey(MyConstants.ARG_POSITION) }?.apply {
            binding.textviewSecond.text = getInt(MyConstants.ARG_POSITION).toString()
        }


        viewModel.getListOne.observe(viewLifecycleOwner, Observer { data ->
            binding.textviewSecond.text = data.toString()

        })

        binding.buttonSecond.setOnClickListener {
            viewModel.fetchListOne()
        }
    }


}

ListTwoFragment.kt

class ListTwoFragment : Fragment() {

    companion object {
        private const val TAG = "ListTwoFragment"
    }

    private var _binding: FragmentSecondBinding? = null
    private val binding get() = _binding!!

    private val viewModel by activityViewModels<MyViewModel>()


    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View {
        _binding = FragmentSecondBinding.inflate(inflater, container, false)
        return binding.root
    }

    override fun onDestroyView() {
        super.onDestroyView()
        _binding = null
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)

        arguments?.takeIf { it.containsKey(MyConstants.ARG_POSITION) }?.apply {
            binding.textviewSecond.text = getInt(MyConstants.ARG_POSITION).toString()
        }


        viewModel.getListTwo.observe(viewLifecycleOwner, Observer { data ->
            binding.textviewSecond.text = data.toString()

        })

        binding.buttonSecond.setOnClickListener {
            viewModel.fetchListTwo()
        }
    }


}

MyViewModel.kt

class MyViewModel : ViewModel() {
    companion object {
        private const val TAG = "MyViewModel"
    }

    private val _mListOne: MutableLiveData<List<String>> = MutableLiveData()
    val getListOne: LiveData<List<String>>
        get() = _mListOne

    private val _mListTwo: MutableLiveData<List<String>> = MutableLiveData()
    val getListTwo: LiveData<List<String>>
        get() = _mListTwo



    private val _mCountList: SparseArray<Int> = SparseArray()
    private val _countList: MutableLiveData<SparseArray<Int>> = MutableLiveData()
    val getCountList: LiveData<SparseArray<Int>>
        get() = _countList


    fun fetchListOne() {
        Log.d(TAG, "fetchListOne: ")

        val mList: MutableList<String> = arrayListOf()
        for (i in 1..15) {
            mList.add("In $i")
        }
        _mListOne.value = mList

        _mCountList.put(0, mList.count())
        _countList.value = _mCountList
    }


    fun fetchListTwo() {
        Log.d(TAG, "fetchListTwo: ")
        val mList: MutableList<String> = arrayListOf()
        for (i in 1..25) {
            mList.add("Out $i")
        }
        _mListTwo.value = mList

        _mCountList.put(1, mList.count())
        _countList.value = _mCountList
    }


}