added a ViewPager2 to switch between page fragments

added a PagerAdapter (FragmentStateAdapter) to provide the fragments for the ViewPager2
added the necessary fragments
added the necessary listeners for the TabLayout and the ViewPager2

app/src/main/java/de/chrissthecoder/store/adapter/DashboardFragmentPagerAdapter.kt

@@ -0,0 +1,20 @@
+package de.chrissthecoder.store.adapter
+
+import androidx.fragment.app.Fragment
+import androidx.fragment.app.FragmentManager
+import androidx.lifecycle.Lifecycle
+import androidx.viewpager2.adapter.FragmentStateAdapter
+import de.chrissthecoder.store.ui.dashboard.tabfragment.ShoppinglistFragment
+import de.chrissthecoder.store.ui.dashboard.tabfragment.UnderstockFragment
+
+class DashboardFragmentPagerAdapter(manager: FragmentManager, lifecycle: Lifecycle) : FragmentStateAdapter(manager, lifecycle) {
+
+    override fun getItemCount() : Int {
+        return 2
+    }
+
+    override fun createFragment(position: Int) : Fragment {
+        return  if(position == 0)   { ShoppinglistFragment() }
+                else                { UnderstockFragment() }
+    }
+}

app/src/main/java/de/chrissthecoder/store/ui/dashboard/DashboardFragment.kt

@@ -6,26 +6,53 @@ import android.view.View
 import android.view.ViewGroup
 import androidx.fragment.app.Fragment
 import androidx.lifecycle.ViewModelProvider
+import androidx.viewpager2.widget.ViewPager2
+import androidx.viewpager2.widget.ViewPager2.OnPageChangeCallback
+import com.google.android.material.tabs.TabLayout
+import com.google.android.material.tabs.TabLayout.OnTabSelectedListener
+import de.chrissthecoder.store.adapter.DashboardFragmentPagerAdapter
 import de.chrissthecoder.store.databinding.FragmentDashboardBinding
 
 class DashboardFragment : Fragment() {
 
     private var _binding: FragmentDashboardBinding? = null
-
-    // This property is only valid between onCreateView and
-    // onDestroyView.
     private val binding get() = _binding!!
 
-    override fun onCreateView(
+    private lateinit var tabLayout: TabLayout
-        inflater: LayoutInflater,
+    private lateinit var viewPager: ViewPager2
-        container: ViewGroup?,
+    private lateinit var adapter: DashboardFragmentPagerAdapter
-        savedInstanceState: Bundle?
-    ): View {
-        val dashboardViewModel = ViewModelProvider(this).get(DashboardViewModel::class.java)
 
+    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?) : View {
         _binding = FragmentDashboardBinding.inflate(inflater, container, false)
         val root: View = binding.root
 
+        val dashboardViewModel = ViewModelProvider(this).get(DashboardViewModel::class.java)
+
+        tabLayout = binding.tabLayout
+        viewPager = binding.viewPager
+        adapter = DashboardFragmentPagerAdapter(parentFragmentManager, lifecycle)
+        viewPager.adapter = adapter
+
+        tabLayout.addOnTabSelectedListener(object : OnTabSelectedListener {
+            override fun onTabSelected(tab: TabLayout.Tab?) {
+                if (tab != null) {
+                    viewPager.currentItem = tab.position
+                }
+            }
+
+            override fun onTabUnselected(tab: TabLayout.Tab?) { }
+            override fun onTabReselected(tab: TabLayout.Tab?) { }
+        })
+
+        viewPager.registerOnPageChangeCallback(object : OnPageChangeCallback() {
+            override fun onPageSelected(position: Int) {
+                super.onPageSelected(position)
+                tabLayout.selectTab(tabLayout.getTabAt(position))
+            }
+        })
+
+
+
         return root
     }
 

app/src/main/java/de/chrissthecoder/store/ui/dashboard/tabfragment/ShoppinglistFragment.kt

@@ -0,0 +1,60 @@
+package de.chrissthecoder.store.ui.dashboard.tabfragment
+
+import android.os.Bundle
+import androidx.fragment.app.Fragment
+import android.view.LayoutInflater
+import android.view.View
+import android.view.ViewGroup
+import de.chrissthecoder.store.R
+
+// TODO: Rename parameter arguments, choose names that match
+// the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
+private const val ARG_PARAM1 = "param1"
+private const val ARG_PARAM2 = "param2"
+
+/**
+ * A simple [Fragment] subclass.
+ * Use the [ShoppinglistFragment.newInstance] factory method to
+ * create an instance of this fragment.
+ */
+class ShoppinglistFragment : Fragment() {
+    // TODO: Rename and change types of parameters
+    private var param1: String? = null
+    private var param2: String? = null
+
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+        arguments?.let {
+            param1 = it.getString(ARG_PARAM1)
+            param2 = it.getString(ARG_PARAM2)
+        }
+    }
+
+    override fun onCreateView(
+        inflater: LayoutInflater, container: ViewGroup?,
+        savedInstanceState: Bundle?
+    ): View? {
+        // Inflate the layout for this fragment
+        return inflater.inflate(R.layout.fragment_shoppinglist, container, false)
+    }
+
+    companion object {
+        /**
+         * Use this factory method to create a new instance of
+         * this fragment using the provided parameters.
+         *
+         * @param param1 Parameter 1.
+         * @param param2 Parameter 2.
+         * @return A new instance of fragment ShoppinglistFragment.
+         */
+        // TODO: Rename and change types and number of parameters
+        @JvmStatic
+        fun newInstance(param1: String, param2: String) =
+            ShoppinglistFragment().apply {
+                arguments = Bundle().apply {
+                    putString(ARG_PARAM1, param1)
+                    putString(ARG_PARAM2, param2)
+                }
+            }
+    }
+}

app/src/main/java/de/chrissthecoder/store/ui/dashboard/tabfragment/UnderstockFragment.kt

@@ -0,0 +1,60 @@
+package de.chrissthecoder.store.ui.dashboard.tabfragment
+
+import android.os.Bundle
+import androidx.fragment.app.Fragment
+import android.view.LayoutInflater
+import android.view.View
+import android.view.ViewGroup
+import de.chrissthecoder.store.R
+
+// TODO: Rename parameter arguments, choose names that match
+// the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
+private const val ARG_PARAM1 = "param1"
+private const val ARG_PARAM2 = "param2"
+
+/**
+ * A simple [Fragment] subclass.
+ * Use the [UnderstockFragment.newInstance] factory method to
+ * create an instance of this fragment.
+ */
+class UnderstockFragment : Fragment() {
+    // TODO: Rename and change types of parameters
+    private var param1: String? = null
+    private var param2: String? = null
+
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+        arguments?.let {
+            param1 = it.getString(ARG_PARAM1)
+            param2 = it.getString(ARG_PARAM2)
+        }
+    }
+
+    override fun onCreateView(
+        inflater: LayoutInflater, container: ViewGroup?,
+        savedInstanceState: Bundle?
+    ): View? {
+        // Inflate the layout for this fragment
+        return inflater.inflate(R.layout.fragment_understock, container, false)
+    }
+
+    companion object {
+        /**
+         * Use this factory method to create a new instance of
+         * this fragment using the provided parameters.
+         *
+         * @param param1 Parameter 1.
+         * @param param2 Parameter 2.
+         * @return A new instance of fragment UnderstockFragment.
+         */
+        // TODO: Rename and change types and number of parameters
+        @JvmStatic
+        fun newInstance(param1: String, param2: String) =
+            UnderstockFragment().apply {
+                arguments = Bundle().apply {
+                    putString(ARG_PARAM1, param1)
+                    putString(ARG_PARAM2, param2)
+                }
+            }
+    }
+}

app/src/main/res/layout/fragment_dashboard.xml

@@ -7,6 +7,7 @@
     tools:context=".ui.dashboard.DashboardFragment">
 
     <com.google.android.material.tabs.TabLayout
+        android:id="@+id/tabLayout"
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         app:layout_constraintBottom_toBottomOf="parent"
@@ -24,4 +25,15 @@
             android:text="@string/tab_understock" />
 
     </com.google.android.material.tabs.TabLayout>
+
+    <androidx.viewpager2.widget.ViewPager2
+        android:id="@+id/viewPager"
+        android:layout_width="0dp"
+        android:layout_height="0dp"
+        app:layout_constraintBottom_toBottomOf="parent"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintHorizontal_bias="0.5"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toBottomOf="@+id/tabLayout" />
+
 </androidx.constraintlayout.widget.ConstraintLayout>

app/src/main/res/layout/fragment_shoppinglist.xml

@@ -0,0 +1,19 @@
+<?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=".ui.dashboard.tabfragment.ShoppinglistFragment">
+
+    <TextView
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:text="Einkaufszettel"
+        android:textAlignment="center"
+        android:textSize="32sp"
+        app:layout_constraintBottom_toBottomOf="parent"
+        app:layout_constraintTop_toTopOf="parent"
+        app:layout_constraintVertical_bias="0.5" />
+
+</androidx.constraintlayout.widget.ConstraintLayout>

app/src/main/res/layout/fragment_understock.xml

@@ -0,0 +1,19 @@
+<?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=".ui.dashboard.tabfragment.UnderstockFragment">
+
+    <TextView
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:text="Minderbestand"
+        android:textAlignment="center"
+        android:textSize="32sp"
+        app:layout_constraintBottom_toBottomOf="parent"
+        app:layout_constraintTop_toTopOf="parent"
+        app:layout_constraintVertical_bias="0.5" />
+
+</androidx.constraintlayout.widget.ConstraintLayout>