使用ViewPager FragmentTransaction进行表格布局

我有一张带寻呼机的表格。我的ViewPager中的片段包含一个RecyclerView,我试图在进行选择时显示一个新片段。它似乎正在创建新的片段,但我没有看到它。我做错了什么?

activity_tabs.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"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@drawable/background_gradient">

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <androidx.appcompat.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="@color/transparent"
            app:popupTheme="@style/AppTheme.PopupOverlay" />

        <com.google.android.material.tabs.TabLayout
            android:id="@+id/tabLayout"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_below="@id/toolbar"
            android:elevation="6dp"
            android:foregroundTint="@color/white"
            app:tabTextColor="@color/white"
            app:tabIconTint="@color/white"
            app:tabIndicatorColor="@color/white">
        </com.google.android.material.tabs.TabLayout>

        <androidx.viewpager.widget.ViewPager
            android:id="@+id/viewPager"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_below="@id/tabLayout">
        </androidx.viewpager.widget.ViewPager>

    </RelativeLayout>

</androidx.constraintlayout.widget.ConstraintLayout>

class TabActivity: AppCompatActivity() {

    lateinit var tabLayout: TabLayout
    private var tabIcons = intArrayOf(
            R.drawable.collections_icon,
            R.drawable.user_icon,
            R.drawable.settings_icon
        )

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_tabs)
        setSupportActionBar(findViewById(R.id.toolbar))
        supportActionBar?.title = null
        supportActionBar?.setDisplayHomeAsUpEnabled(false)

        tabLayout = findViewById<TabLayout>(R.id.tabLayout)
        tabLayout.addTab(tabLayout.newTab().setText(""))
        tabLayout.addTab(tabLayout.newTab().setText(""))
        tabLayout.addTab(tabLayout.newTab().setText(""))
        tabLayout.tabGravity = TabLayout.GRAVITY_FILL

        var viewPager = findViewById<ViewPager>(R.id.viewPager)
        var pagerAdapter = PagerAdapter(supportFragmentManager, tabLayout.tabCount)
        viewPager.adapter = pagerAdapter

        tabLayout.setupWithViewPager(viewPager)
        setupTabs()
    }

    private fun setupTabs() {
        tabLayout.getTabAt(0)?.setIcon(tabIcons[0])?.setText("Collections")
        tabLayout.getTabAt(1)?.setIcon(tabIcons[1])?.setText("Account")
        tabLayout.getTabAt(2)?.setIcon(tabIcons[2])?.setText("Settings")
    }
}

PagerAdapter.kt

class PagerAdapter(fragmentManager: FragmentManager, private val numOfTabs: Int): FragmentStatePagerAdapter(fragmentManager) {
    override fun getItem(position: Int): Fragment {
        if (position == 0) {
            println("TAB 1")
            var tabOne = CollectionsFragment()
            return tabOne
        } else if (position == 1) {
            println("TAB 2")
            var tabTwo = CollectionsFragment()
            return tabTwo
        } else {
            println("TAB 3")
            var tabThree = CollectionsFragment()
            return tabThree
        }
    }

    override fun getCount(): Int {
        return numOfTabs
    }
}

CollectionsFragment.kt

class CollectionsFragment: Fragment() {
    private lateinit var recylclerView: RecyclerView
    private lateinit var viewAdapter: RecyclerView.Adapter<*>
    private lateinit var viewManager: RecyclerView.LayoutManager
    private lateinit var progressBar: ProgressBar
    private lateinit var auth: FirebaseAuth
    private var collections = ArrayList<Collection>()

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
        super.onCreateView(inflater, container, savedInstanceState)
        val rootView = inflater.inflate(R.layout.fragment_collections, container, false)

        auth = FirebaseAuth.getInstance()

        progressBar = rootView.findViewById(R.id.progressBar)
        progressBar.isVisible = true

        viewManager = LinearLayoutManager(rootView.context)
        viewAdapter = CollectionAdapter(collections)

        recylclerView = rootView.findViewById<RecyclerView>(R.id.recycler_view).apply{
            setHasFixedSize(true)
            layoutManager = viewManager
            adapter = viewAdapter
        }

        getCollections()

        return rootView
    }

    fun getCollections() {
        var userId = auth.currentUser?.uid
        FirebaseFirestore.getInstance().collection("collections").whereEqualTo("user_id", userId).orderBy("name")
            .addSnapshotListener { value, e ->
                if (e != null) {
                    Log.w("ERROR", "Listen failed.", e)
                    return@addSnapshotListener
                }

                for (doc in value!!) {
                    var collection = Collection(doc.id, doc.getString("name")!!)
                    collections.add(collection)
                }

                // Reload recyclerview data
                recylclerView.adapter?.notifyDataSetChanged()
                progressBar.isVisible = false
            }
    }

    
    inner class CollectionAdapter(private val dataset: ArrayList<Collection>): RecyclerView.Adapter<CollectionAdapter.CollectionViewHolder>() {
        inner class CollectionViewHolder(val view: View): RecyclerView.ViewHolder(view), View.OnClickListener {

            init {
                view.setOnClickListener(this)
            }

            override fun onClick(p0: View?) {
                println("TAPPED")
                var itemsFragment = ItemsFragment()
                itemsFragment.selectedCollection = dataset[layoutPosition]
                val fragmentTransaction = activity?.supportFragmentManager?.beginTransaction()
                println(fragmentTransaction)
                fragmentTransaction?.add(R.id.viewPager, itemsFragment)
                
                fragmentTransaction?.addToBackStack(null)
                fragmentTransaction?.commit()
            }

        }

        override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): CollectionAdapter.CollectionViewHolder {
            val view = LayoutInflater.from(parent.context).inflate(R.layout.collection_item, parent, false)
            return CollectionViewHolder(view)
        }

        override fun onBindViewHolder(holder: CollectionViewHolder, position: Int) {
            var name = dataset[position].name
          
            val textView = holder.view.findViewById<TextView>(R.id.collectionName)
            textView.text = name
        }

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