Updated EventPageFragment.kt to have access to its own ViewModel and, by extension, its own reference to the database, which forgoes the need to transport data from EventFragment.kt through StudIPEventPageAdapter.kt to EventPageFragment.kt and allows for filtering for a specific day's items through the database rather than needing to iterate through the list via an extension function manually. Also implemented DiffUtil to perform individual updates rather than calling notifyDataSetChanged() every time a single item has been changed.

app/src/main/java/com/denizk0461/studip/adapter/CanteenOfferPageAdapter.kt

@@ -20,7 +20,7 @@ import com.denizk0461.studip.model.CanteenOfferGroup
  * @param displayAllergens  whether the user wants allergens to be marked
  */
 class CanteenOfferPageAdapter(
-    val fragmentActivity: FragmentActivity,
+    fragmentActivity: FragmentActivity,
     private var offers: List<CanteenOfferGroup>,
     private var daysCovered: Int,
     private val onClickListener: CanteenOfferItemAdapter.OnClickListener,

app/src/main/java/com/denizk0461/studip/adapter/StudIPEventItemAdapter.kt

@@ -3,7 +3,9 @@ package com.denizk0461.studip.adapter
 import android.content.res.ColorStateList
 import android.view.LayoutInflater
 import android.view.ViewGroup
+import androidx.recyclerview.widget.DiffUtil
 import androidx.recyclerview.widget.RecyclerView
+import com.denizk0461.studip.data.AppDiffUtilCallback
 import com.google.android.material.R
 import com.denizk0461.studip.data.getThemedColor
 import com.denizk0461.studip.data.parseToMinutes
@@ -12,29 +14,30 @@ import com.denizk0461.studip.databinding.ItemEventBinding
 import java.util.*
 
 /**
- * Custom RecyclerView adapter that lays out the Stud.IP events of a given day.
+ * Custom RecyclerView adapter that lays out the Stud.IP events for a given day.
  *
- * @param events            list of all events (still not filtered by day at this point)
+
- * @param currentDay        current day that is used to show only events of a given day (0 = Monday,
+ * @param currentDay        current day that is used to show only a given day's events (0 = Monday,
  *                          4 = Friday)
  * @param onClickListener   used for listening to clicks and long presses
  */
 class StudIPEventItemAdapter(
-    events: List<StudIPEvent>,
     private val currentDay: Int,
     private val onClickListener: OnClickListener,
 ) : RecyclerView.Adapter<StudIPEventItemAdapter.EventViewHolder>() {
 
-    // Filter events to only show those of a given day
+    /**
-    private val filteredEvents: List<StudIPEvent> = events.filter { it.day == currentDay }
+     * List of all events (still not filtered by day at this point)
+     */
+    private var events: MutableList<StudIPEvent> = mutableListOf()
 
-    /*
+    /**
      * Retrieve an instance of Calendar to check whether the adapter's day matches the current day.
-     * TODO this can be optimised by checking in StudIPEventPageAdapter.kt and delivering a boolean
+     * TODO this can be optimised by checking in EventPageFragment.kt and delivering a boolean
      */
     private val currentCalendar = Calendar.getInstance()
 
-    /*
+    /**
      * Used to disallow highlighting more than one course at a time, since only a single course
      * could be coming up at a given time.
      */
@@ -58,12 +61,11 @@ class StudIPEventItemAdapter(
     }
 
     // Set the amount of items to the size of the filtered list, so only events of the current day
-    override fun getItemCount(): Int = filteredEvents.size
+    override fun getItemCount(): Int = events.size
 
-    // TODO inflate a view saying "no events" if none are available for a given day
     override fun onBindViewHolder(holder: EventViewHolder, position: Int) {
         // Retrieve item for current position
-        val currentItem = filteredEvents[position]
+        val currentItem = events[position]
 
         // Set up text fields with corresponding values
         holder.binding.textTitle.text = currentItem.title
@@ -117,6 +119,26 @@ class StudIPEventItemAdapter(
         }
     }
 
+    /**
+     * Updates the data and calculates the difference between the old dataset and the newly provided
+     * dataset.
+     *
+     * @param newData   new dataset to be displayed
+     */
+    fun setNewData(newData: List<StudIPEvent>) {
+        // Calculate the difference between the old list and the new list
+        val diffResult = DiffUtil.calculateDiff(AppDiffUtilCallback(events, newData))
+
+        // Remove all items from the list
+        events.clear()
+
+        // Add all items from the new list
+        events.addAll(newData)
+
+        // Tell the DiffUtil which items have changed between the two lists
+        diffResult.dispatchUpdatesTo(this)
+    }
+
     /**
      * Checks if a given course is the next course coming up. This is done by checking whether the
      * day of the course matches the current real world day, as well as by evaluating if the end
@@ -131,7 +153,6 @@ class StudIPEventItemAdapter(
         (calendar.get(Calendar.DAY_OF_WEEK) == this.day.toCalendarDay()) &&
                 ((calendar.get(Calendar.MINUTE) + calendar.get(Calendar.HOUR_OF_DAY) * 60) < this.timeslotEnd.parseToMinutes())
 
-    // Converts day as defined in StudIPEvent.kt to day from Calendar
     /**
      * Converts a numeric value as defined in StudIPEvent.kt to a calendar day. Used to convert from
      * American convention (where Sunday is the first day, 1 = Sunday, 2 = Monday, 7 = Saturday) to

app/src/main/java/com/denizk0461/studip/adapter/StudIPEventPageAdapter.kt

@@ -3,20 +3,15 @@ package com.denizk0461.studip.adapter
 import androidx.fragment.app.Fragment
 import androidx.fragment.app.FragmentActivity
 import androidx.viewpager2.adapter.FragmentStateAdapter
-import com.denizk0461.studip.model.StudIPEvent
 import com.denizk0461.studip.fragment.EventPageFragment
 
 /**
  * Custom ViewPager adapter for managing multiple pages of Stud.IP events.
  *
  * @param fragmentActivity  parent fragment activity
- * @param events            all events (not filtered by day at this point)
- * @param onClickListener   for managing click and long press events
  */
 class StudIPEventPageAdapter(
     fragmentActivity: FragmentActivity,
-    private var events: List<StudIPEvent>,
-    private val onClickListener: StudIPEventItemAdapter.OnClickListener,
 ) : FragmentStateAdapter(fragmentActivity) {
 
     /*
@@ -25,18 +20,5 @@ class StudIPEventPageAdapter(
     override fun getItemCount(): Int = 7
 
     override fun createFragment(position: Int): Fragment =
-        EventPageFragment(events, position, onClickListener)
+        EventPageFragment(position)
-
-    /**
-     * Update the entire list of items
-     *
-     * @param items the new set of items
-     */
-    fun setNewItems(items: List<StudIPEvent>) {
-        // Update items
-        events = items
-
-        // Force an update of the view. TODO replace with individual updates, as this is inefficient
-        notifyDataSetChanged()
-    }
 }

app/src/main/java/com/denizk0461/studip/data/AppDiffUtilCallback.kt

@@ -0,0 +1,50 @@
+package com.denizk0461.studip.data
+
+import androidx.recyclerview.widget.DiffUtil
+
+/**
+ * Utility class used to calculate the difference between two lists to provide the adapter with
+ * means to perform operations only on items that have been newly added/modified/deleted.
+ *
+ * @param oldList   old list
+ * @param newList   new list
+ */
+class AppDiffUtilCallback(
+    private val oldList: List<Any>,
+    private val newList: List<Any>,
+) : DiffUtil.Callback() {
+
+    /**
+     * Get the old list's size count.
+     *
+     * @return  size of the old list
+     */
+    override fun getOldListSize(): Int = oldList.size
+
+    /**
+     * Get the new list's size count.
+     *
+     * @return  size of the new list
+     */
+    override fun getNewListSize(): Int = newList.size
+
+    /**
+     * Check whether two items in the lists contain items of the same class.
+     *
+     * @param oldItemPosition   position of the item in the old list to be checked
+     * @param newItemPosition   position of the item in the new list to be checked
+     * @return                  whether the two items are of the same class
+     */
+    override fun areItemsTheSame(oldItemPosition: Int, newItemPosition: Int): Boolean =
+        oldList[oldItemPosition].javaClass == newList[newItemPosition].javaClass
+
+    /**
+     * Check whether two items in the lists have the same contents.
+     *
+     * @param oldItemPosition   position of the item in the old list to be checked
+     * @param newItemPosition   position of the item in the new list to be checked
+     * @return                  whether the two items are the same (content is equal)
+     */
+    override fun areContentsTheSame(oldItemPosition: Int, newItemPosition: Int): Boolean =
+        oldList[oldItemPosition].hashCode() == newList[newItemPosition].hashCode()
+}

app/src/main/java/com/denizk0461/studip/db/AppDAO.kt

@@ -21,6 +21,14 @@ interface AppDAO {
     @get:Query("SELECT * FROM studipevents ORDER BY timeslotId, id")
     val allEvents: LiveData<List<StudIPEvent>>
 
+    /**
+     * Retrieves Stud.IP events for a specific day, ordered by their timeslots, then their IDs.
+     *
+     * @return  Stud.IP events for a certain day exposed through a LiveData object
+     */
+    @Query("SELECT * FROM studipevents WHERE day = :day ORDER BY timeslotId, id")
+    fun getEventsForDay(day: Int): LiveData<List<StudIPEvent>>
+
     /**
      * Updates a given Stud.IP element.
      *

app/src/main/java/com/denizk0461/studip/db/AppRepository.kt

@@ -26,11 +26,11 @@ class AppRepository(app: Application) {
     private val blankDietaryPrefs: String = DietaryPreferences.C_FALSE.toString().repeat(10)
 
     /**
-     * Retrieves all Stud.IP events.
+     * Retrieves Stud.IP events for a specific day, ordered by their timeslots, then their IDs.
      *
-     * @return all Stud.IP events exposed through a LiveData object
+     * @return  Stud.IP events for a certain day exposed through a LiveData object
      */
-    val allEvents: LiveData<List<StudIPEvent>> = dao.allEvents
+    fun getEventsForDay(day: Int): LiveData<List<StudIPEvent>> = dao.getEventsForDay(day)
 
     /**
      * Inserts a list of Stud.IP events into the database.
@@ -166,13 +166,6 @@ class AppRepository(app: Application) {
      */
     fun nukeOfferDates() { dao.nukeOfferDates() }
 
-    /**
-     * Inserts a date into the database.
-     *
-     * @param date object to be saved to the database
-     */
-    fun insert(date: OfferDate) { dao.insert(date) }
-
     /**
      * Inserts a list of dates into the database.
      *
@@ -180,13 +173,6 @@ class AppRepository(app: Application) {
      */
     fun insertDates(dates: List<OfferDate>) { dao.insertDates(dates) }
 
-    /**
-     * Inserts a canteen into the database.
-     *
-     * @param canteen   object to be saved to the database
-     */
-    fun insert(canteen: OfferCanteen) { dao.insert(canteen) }
-
     /**
      * Inserts a list of canteens into the database.
      *
@@ -194,13 +180,6 @@ class AppRepository(app: Application) {
      */
     fun insertCanteens(canteens: List<OfferCanteen>) { dao.insertCanteens(canteens) }
 
-    /**
-     * Inserts a canteen offer category into the database.
-     *
-     * @param category object to be saved to the database
-     */
-    fun insert(category: OfferCategory) { dao.insert(category) }
-
     /**
      * Inserts a list of categories into the database.
      *
@@ -208,13 +187,6 @@ class AppRepository(app: Application) {
      */
     fun insertCategories(categories: List<OfferCategory>) { dao.insertCategories(categories) }
 
-    /**
-     * Inserts a canteen offer item into the database.
-     *
-     * @param item object to be saved to the database
-     */
-    fun insert(item: OfferItem) { dao.insert(item) }
-
     /**
      * Inserts a list of items into the database.
      *

app/src/main/java/com/denizk0461/studip/fragment/EventFragment.kt

@@ -1,7 +1,6 @@
 package com.denizk0461.studip.fragment
 
 import android.os.Bundle
-import android.os.Parcelable
 import android.util.Log
 import android.view.LayoutInflater
 import android.view.View
@@ -9,11 +8,8 @@ import android.view.ViewGroup
 import androidx.fragment.app.FragmentActivity
 import androidx.fragment.app.viewModels
 import com.denizk0461.studip.R
-import com.denizk0461.studip.adapter.StudIPEventItemAdapter
 import com.denizk0461.studip.adapter.StudIPEventPageAdapter
 import com.denizk0461.studip.databinding.FragmentEventBinding
-import com.denizk0461.studip.model.StudIPEvent
-import com.denizk0461.studip.sheet.ScheduleUpdateSheet
 import com.denizk0461.studip.viewmodel.EventViewModel
 import com.google.android.material.tabs.TabLayoutMediator
 import java.util.*
@@ -73,24 +69,7 @@ class EventFragment : AppFragment() {
         }
 
         // Set up the view pager's adapter
-        viewPagerAdapter =
+        viewPagerAdapter = StudIPEventPageAdapter(activity as FragmentActivity)
-            StudIPEventPageAdapter(activity as FragmentActivity, listOf(), object : StudIPEventItemAdapter.OnClickListener {
-                override fun onClick(event: StudIPEvent) {
-                    // TODO implement functionality or delete
-                }
-                override fun onLongClick(event: StudIPEvent): Boolean {
-                    // Save the current page of the ViewPager
-                    viewPagerPosition = binding.viewPager.currentItem
-
-                    // Open a bottom sheet to edit the event
-                    openBottomSheet(ScheduleUpdateSheet(event, onUpdate = { eventToUpdate ->
-                        viewModel.update(eventToUpdate)
-                    }, onDelete = { eventToDelete ->
-                        viewModel.delete(eventToDelete)
-                    }))
-                    return true
-                }
-            })
 
         // Assign the adapter to the view pager
         binding.viewPager.adapter = viewPagerAdapter
@@ -101,25 +80,25 @@ class EventFragment : AppFragment() {
         }.attach()
 
         // Set up LiveData observer to refresh the view on update
-        viewModel.allEvents.observe(viewLifecycleOwner) { events ->
+//        viewModel.allEvents.observe(viewLifecycleOwner) { events ->
-
+//
-            Log.d("AAAbA?", events.toString())
+//            Log.d("AAAbA?", events.toString())
-
+//
-            // Update the item list in the view pager's adapter
+//            // Update the item list in the view pager's adapter
-            viewPagerAdapter.setNewItems(events)
+//            viewPagerAdapter.setNewItems(events)
-
+//
-            if (!hasFragmentStarted) {
+//            if (!hasFragmentStarted) {
-                // Scroll to the current day, if no page has been stored to be scrolled to
+//                // Scroll to the current day, if no page has been stored to be scrolled to
-                switchToCurrentDayView()
+//                switchToCurrentDayView()
-                hasFragmentStarted = true
+//                hasFragmentStarted = true
-//            } else {
+////            } else {
-//                /*
+////                /*
-//                 * If a page was previously saved, scroll to that one instead. This is meant to
+////                 * If a page was previously saved, scroll to that one instead. This is meant to
-//                 * prevent jumping from
+////                 * prevent jumping from
-//                 */
+////                 */
-//                binding.viewPager.currentItem = viewPagerPosition
+////                binding.viewPager.currentItem = viewPagerPosition
-            }
+//            }
-        }
+//        }
     }
 
     override fun onPause() {

app/src/main/java/com/denizk0461/studip/fragment/EventPageFragment.kt

@@ -4,26 +4,25 @@ import android.os.Bundle
 import android.view.LayoutInflater
 import android.view.View
 import android.view.ViewGroup
+import androidx.fragment.app.viewModels
 import androidx.recyclerview.widget.LinearLayoutManager
 import com.denizk0461.studip.adapter.StudIPEventPageAdapter
 import com.denizk0461.studip.adapter.StudIPEventItemAdapter
 import com.denizk0461.studip.databinding.RecyclerViewBinding
 import com.denizk0461.studip.model.StudIPEvent
+import com.denizk0461.studip.sheet.ScheduleUpdateSheet
+import com.denizk0461.studip.viewmodel.EventPageViewModel
 
 /**
  * Fragment that is instantiated by [StudIPEventPageAdapter] to display individual days' pages and
  * their events.
  *
- * @param events            list of all events (still not filtered by day at this point)
  * @param currentDay    current day that is used to show only events of a given day (0 = Monday,
  *                      4 = Friday)
- * @param onClickListener   used for listening to clicks and long presses
  */
 class EventPageFragment(
-    private val events: List<StudIPEvent>,
     private val currentDay: Int,
-    private val onClickListener: StudIPEventItemAdapter.OnClickListener,
+) : AppFragment(), StudIPEventItemAdapter.OnClickListener {
-) : AppFragment() {
 
     // Nullable view binding reference
     private var _binding: RecyclerViewBinding? = null
@@ -34,6 +33,14 @@ class EventPageFragment(
      */
     private val binding get() = _binding!!
 
+    // View model reference for providing access to the database
+    private val viewModel: EventPageViewModel by viewModels()
+
+    /**
+     * Adapter that manages the page's items
+     */
+    private val eventAdapter = StudIPEventItemAdapter(currentDay, this)
+
     // Instantiate the view binding
     override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View {
         _binding = RecyclerViewBinding.inflate(inflater, container, false)
@@ -49,12 +56,32 @@ class EventPageFragment(
 
             /*
              * Create new adapter for every page. Attribute position denotes day that will be set up
-             * by the newly created adapter (0 = Monday, 4 = Friday)
+             * by the newly created adapter (0 = Monday, 4 = Friday, 6 = Sunday)
              */
-            adapter = StudIPEventItemAdapter(events, currentDay, onClickListener) // TODO check if empty
+            adapter = eventAdapter
 
             // Animate creation of new page
             scheduleLayoutAnimation()
         }
+
+        // Set up LiveData observer to refresh the view on update
+        viewModel.getEventsForDay(currentDay).observe(viewLifecycleOwner) { events ->
+//            eventAdapter.setNewItems(events)
+            eventAdapter.setNewData(events)
+        }
+    }
+
+    override fun onClick(event: StudIPEvent) {
+        // TODO implement functionality or delete
+    }
+
+    override fun onLongClick(event: StudIPEvent): Boolean {
+        // Open a bottom sheet to edit the event
+        openBottomSheet(ScheduleUpdateSheet(event, onUpdate = { eventToUpdate ->
+            viewModel.update(eventToUpdate)
+        }, onDelete = { eventToDelete ->
+            viewModel.delete(eventToDelete)
+        }))
+        return true
     }
 }

app/src/main/java/com/denizk0461/studip/model/StudIPEvent.kt

@@ -37,7 +37,7 @@ data class StudIPEvent(
      */
     fun timeslot(): String = "$timeslotStart – $timeslotEnd"
 
-    // Auto-generated methods
+    // Auto-generated methods. Necessary for [AppDiffUtilCallback]
 
     override fun equals(other: Any?): Boolean {
         if (this === other) return true
@@ -45,11 +45,19 @@ data class StudIPEvent(
 
         other as StudIPEvent
 
+        if (id != other.id) return false
         if (title != other.title) return false
-        if (!lecturer.contentEquals(other.lecturer)) return false
+        if (lecturer != other.lecturer) return false
+        if (room != other.room) return false
+        if (day != other.day) return false
+        if (timeslotStart != other.timeslotStart) return false
+        if (timeslotEnd != other.timeslotEnd) return false
+        if (timeslotId != other.timeslotId) return false
+        if (colour != other.colour) return false
 
         return true
     }
+
     override fun hashCode(): Int {
         var result = id
         result = 31 * result + title.hashCode()
@@ -58,7 +66,8 @@ data class StudIPEvent(
         result = 31 * result + day
         result = 31 * result + timeslotStart.hashCode()
         result = 31 * result + timeslotEnd.hashCode()
-        result = 31 * result + colour.hashCode()
+        result = 31 * result + timeslotId
+        result = 31 * result + colour
         return result
     }
 }

app/src/main/java/com/denizk0461/studip/viewmodel/EventPageViewModel.kt

@@ -0,0 +1,34 @@
+package com.denizk0461.studip.viewmodel
+
+import android.app.Application
+import androidx.lifecycle.LiveData
+import com.denizk0461.studip.model.StudIPEvent
+
+/**
+ * View model for [com.denizk0461.studip.fragment.EventPageFragment]
+ *
+ * @param app   reference to the app
+ */
+class EventPageViewModel(app: Application) : AppViewModel(app) {
+
+    /**
+     * Retrieves Stud.IP events for a specific day, ordered by their timeslots, then their IDs.
+     *
+     * @return  Stud.IP events for a certain day exposed through a LiveData object
+     */
+    fun getEventsForDay(day: Int): LiveData<List<StudIPEvent>> = repo.getEventsForDay(day)
+
+    /**
+     * Updates a schedule element.
+     *
+     * @param event the event to update
+     */
+    fun update(event: StudIPEvent) { doAsync { repo.update(event) } }
+
+    /**
+     * Deletes a schedule element.
+     *
+     * @param event the event to delete
+     */
+    fun delete(event: StudIPEvent) { doAsync { repo.delete(event) } }
+}

app/src/main/java/com/denizk0461/studip/viewmodel/EventViewModel.kt

@@ -1,34 +1,10 @@
 package com.denizk0461.studip.viewmodel
 
 import android.app.Application
-import androidx.lifecycle.LiveData
-import com.denizk0461.studip.model.StudIPEvent
 
 /**
  * View model for [com.denizk0461.studip.fragment.EventFragment]
  *
  * @param app   reference to the app
  */
-class EventViewModel(app: Application) : AppViewModel(app) {
+class EventViewModel(app: Application) : AppViewModel(app)
-
-    /**
-     * Retrieves all Stud.IP events.
-     *
-     * @return all Stud.IP events exposed through a LiveData object
-     */
-    val allEvents: LiveData<List<StudIPEvent>> = repo.allEvents
-
-    /**
-     * Updates a schedule element.
-     *
-     * @param event the event to update
-     */
-    fun update(event: StudIPEvent) { doAsync { repo.update(event) } }
-
-    /**
-     * Deletes a schedule element.
-     *
-     * @param event the event to delete
-     */
-    fun delete(event: StudIPEvent) { doAsync { repo.delete(event) } }
-}