Edited canteen views to have direct database access in the CanteenPageFragment.kt, allowing for filtering the individual days through the database; filtering now works (with changes animated!!) through updating a LiveData and observing it in the page fragment

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

@@ -3,8 +3,10 @@ package com.denizk0461.studip.adapter
 import android.view.LayoutInflater
 import android.view.ViewGroup
 import androidx.appcompat.content.res.AppCompatResources
+import androidx.recyclerview.widget.DiffUtil
 import androidx.recyclerview.widget.RecyclerView
 import com.denizk0461.studip.R
+import com.denizk0461.studip.data.AppDiffUtilCallback
 import com.denizk0461.studip.databinding.ItemCanteenBinding
 import com.denizk0461.studip.databinding.ItemCanteenLineBinding
 import com.denizk0461.studip.databinding.ItemIconBinding
@@ -15,16 +17,16 @@ import com.denizk0461.studip.model.DietaryPreferences
 /**
  * Custom RecyclerView adapter that lays out the offers of a given canteen on a given day.
  *
- * @param offers            list of all offers filtered by canteen and day, grouped by category
  * @param onClickListener   used for listening to clicks and long presses
  * @param displayAllergens  whether the user wants allergens to be marked
  */
 class CanteenOfferItemAdapter(
-    private val offers: List<CanteenOfferGroup>,
     private val onClickListener: OnClickListener,
     private val displayAllergens: Boolean,
 ) : RecyclerView.Adapter<CanteenOfferItemAdapter.OfferViewHolder>() {
 
+    private val offers: MutableList<CanteenOfferGroup> = mutableListOf()
+
     /**
      * View holder class for parent class
      *
@@ -121,7 +123,7 @@ class CanteenOfferItemAdapter(
                 }
 
                 // If no dietary preferences are met, set the view to display a neutral icon
-                if (indices.isEmpty()) indices.add(10)
+                if (indices.isEmpty()) indices.add(DietaryPreferences.NONE.ordinal)
 
                 // Iterate through all icons that need to be displayed
                 indices.forEach { index ->
@@ -157,6 +159,26 @@ class CanteenOfferItemAdapter(
         }
     }
 
+    /**
+     * 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<CanteenOfferGroup>) {
+        // Calculate the difference between the old list and the new list
+        val diffResult = DiffUtil.calculateDiff(AppDiffUtilCallback(offers, newData))
+
+        // Remove all items from the list
+        offers.clear()
+
+        // Add all items from the new list
+        offers.addAll(newData)
+
+        // Tell the DiffUtil which items have changed between the two lists
+        diffResult.dispatchUpdatesTo(this)
+    }
+
     /**
      * Adds a star to mark allergens present in an offer. Allergens will be displayed as a star '*'
      * next to the title.

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

@@ -4,53 +4,29 @@ import androidx.fragment.app.Fragment
 import androidx.fragment.app.FragmentActivity
 import androidx.viewpager2.adapter.FragmentStateAdapter
 import com.denizk0461.studip.fragment.CanteenPageFragment
-import com.denizk0461.studip.model.CanteenOfferGroup
 
 
 /**
  * Custom ViewPager adapter for managing multiple pages of canteen offers.
  *
  * @param fragmentActivity  parent fragment activity
- * @param offers            all offers for a given canteen, grouped by category (not filtered by day at
- *                          this point)
- * @param daysCovered       tells for how many days offers are available for.
- *                          Example: if the next two weeks are available, Monday through Friday and
- *                          excluding weekends, this value should be 10.
- * @param onClickListener   for managing click and long press events
- * @param displayAllergens  whether the user wants allergens to be marked
  */
 class CanteenOfferPageAdapter(
     fragmentActivity: FragmentActivity,
-    private var offers: List<CanteenOfferGroup>,
-    private var daysCovered: Int,
-    private val onClickListener: CanteenOfferItemAdapter.OnClickListener,
-    private val displayAllergens: Boolean,
 ) : FragmentStateAdapter(fragmentActivity) {
 
+    private var count: Int = 0
+
     // Returns the count of days covered
-    override fun getItemCount(): Int = daysCovered
+    override fun getItemCount(): Int = count
 
     override fun createFragment(position: Int): Fragment =
         CanteenPageFragment(
-            offers,
-            onClickListener,
-            displayAllergens,
             position,
         )
 
-    /**
+    fun setItemCount(newCount: Int) {
-     * Update the entire list of items
+        count = newCount
-     *
-     * @param items the new set of items
-     */
-    fun setNewItems(items: List<CanteenOfferGroup>, daysCovered: Int) {
-        // Update the count of days covered
-        this.daysCovered = daysCovered
-
-        // Update items
-        offers = items
-
-        // Force an update of the view. TODO replace with individual updates, as this is inefficient
         notifyDataSetChanged()
     }
 }

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

@@ -29,7 +29,7 @@ class StudIPEventItemAdapter(
     /**
      * List of all events.
      */
-    private var events: MutableList<StudIPEvent> = mutableListOf()
+    private val events: MutableList<StudIPEvent> = mutableListOf()
 
     /**
      * Retrieve an instance of Calendar to check whether the adapter's day matches the current day.

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

@@ -240,7 +240,7 @@ class StwParser(application: Application) {
                         categoryId,
                         title = "NO\$ITEMS",
                         price = "",
-                        dietaryPreferences = "..........",
+                        dietaryPreferences = "tttttttttt",
                         allergens = "",
                     )
                 )
@@ -324,7 +324,6 @@ class StwParser(application: Application) {
             text = text.substring(0 until indexSupOpen) +
                     text.substring((indexSupClose + 6) until text.length)
         }
-
         /*
          * Return the stripped and updated HTML string and join the allergen list to a cohesive
          * string without duplication.

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

@@ -97,6 +97,30 @@ interface AppDAO {
     )
     fun getOffersByPreference(prefs: String): LiveData<List<CanteenOffer>>
 
+    /**
+     * Retrieves all canteen offers that match given day. Objects will be joined through their
+     * primary/foreign keys from instances of OfferDate.kt, OfferCanteen.kt, OfferCategory.kt, and
+     * OfferItem.kt.
+     *
+     * @return all canteen offers matching the given day exposed through a LiveData object
+     */
+    @Query(
+        "SELECT * FROM offer_item " +
+                "JOIN offer_category ON offer_item.categoryId = offer_category.id " +
+                "JOIN offer_canteen ON offer_category.canteenId = offer_canteen.id " +
+                "JOIN offer_date ON offer_category.dateId = offer_date.id " +
+                "WHERE dateId = :day "
+    )
+    fun getOffersByDay(day: Int): LiveData<List<CanteenOffer>>
+
+    /**
+     * Retrieves the amount of dates represented in the offers stored locally. Can be observed.
+     *
+     * @return  date count as LiveData
+     */
+    @Query("SELECT COUNT(*) FROM offer_date")
+    fun getDateCount(): LiveData<Int>
+
     /**
      * Retrieves all canteen offer date objects.
      *

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

@@ -2,6 +2,7 @@ package com.denizk0461.studip.db
 
 import android.app.Application
 import androidx.lifecycle.LiveData
+import androidx.lifecycle.MutableLiveData
 import androidx.preference.PreferenceManager
 import com.denizk0461.studip.model.*
 
@@ -25,6 +26,11 @@ class AppRepository(app: Application) {
     // Blank dietary preference regular expression
     private val blankDietaryPrefs: String = DietaryPreferences.C_FALSE.toString().repeat(10)
 
+    /**
+     * Used to observe just to register an update of the user-set dietary preferences.
+     */
+    val dietaryPreferencesUpdate: MutableLiveData<Int> = MutableLiveData(0)
+
     companion object {
         /**
          * Reference to the app's repository. It is only instantiated once because it can only be
@@ -79,6 +85,20 @@ class AppRepository(app: Application) {
      */
     val allOffers: LiveData<List<CanteenOffer>> = dao.allOffers
 
+    /**
+     * Retrieves all canteen offers that match given day.
+     *
+     * @return all canteen offers matching the given day exposed through a LiveData object
+     */
+    fun getOffersByDay(day: Int): LiveData<List<CanteenOffer>> = dao.getOffersByDay(day)
+
+    /**
+     * Retrieves the amount of dates represented in the offers stored locally. Can be observed.
+     *
+     * @return  date count as LiveData
+     */
+    fun getDateCount(): LiveData<Int> = dao.getDateCount()
+
     /**
      * Updates a schedule element.
      *

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

@@ -8,11 +8,9 @@ import androidx.appcompat.widget.PopupMenu
 import androidx.fragment.app.FragmentActivity
 import androidx.fragment.app.viewModels
 import com.denizk0461.studip.R
-import com.denizk0461.studip.adapter.CanteenOfferItemAdapter
 import com.denizk0461.studip.adapter.CanteenOfferPageAdapter
 import com.denizk0461.studip.databinding.FragmentCanteenBinding
 import com.denizk0461.studip.model.*
-import com.denizk0461.studip.sheet.AllergenSheet
 import com.denizk0461.studip.sheet.TextSheet
 import com.denizk0461.studip.viewmodel.CanteenViewModel
 import com.google.android.material.tabs.TabLayoutMediator
@@ -21,7 +19,7 @@ import com.google.android.material.tabs.TabLayoutMediator
  * User-facing fragment view that displays the canteen offers from the website of the
  * Studierendenwerk Bremen.
  */
-class CanteenFragment : AppFragment(), CanteenOfferItemAdapter.OnClickListener {
+class CanteenFragment : AppFragment() {
 
     // Nullable view binding reference
     private var _binding: FragmentCanteenBinding? = null
@@ -83,7 +81,7 @@ class CanteenFragment : AppFragment(), CanteenOfferItemAdapter.OnClickListener {
                     binding.swipeRefreshLayout.isRefreshing = true
 
                     // Refresh the canteen menu for the newly selected canteen
-                    refresh()
+//                    refresh()
                     true
                 }
                 inflate(R.menu.menu_canteens)
@@ -148,40 +146,41 @@ class CanteenFragment : AppFragment(), CanteenOfferItemAdapter.OnClickListener {
         // Set up the view pager's adapter
         viewPagerAdapter = CanteenOfferPageAdapter(
             activity as FragmentActivity,
-            listOf(),
-            0,
-            this,
-            viewModel.preferenceAllergen,
         )
 
+        viewModel.getDateCount().observe(viewLifecycleOwner) { dateCount ->
+            viewPagerAdapter.itemCount = dateCount
+            binding.swipeRefreshLayout.isRefreshing = false
+        }
+
         // Assign the adapter to the view pager
         binding.viewPager.adapter = viewPagerAdapter
 
         // Set up LiveData observer to refresh the view on update
-        viewModel.allOffers.observe(viewLifecycleOwner) { offers ->
+//        viewModel.allOffers.observe(viewLifecycleOwner) { offers ->
-            // Update the element list stored in this fragment
+//            // Update the element list stored in this fragment
-            elements = offers
+//            elements = offers
-
+//
-            // Group elements by category
+//            // Group elements by category
-            val groupedElements = offers.groupElements().distinct()
+//            val groupedElements = offers.groupElements().distinct()
-
+//
-            // Find all dates for which items are available
+//            // Find all dates for which items are available
-            val newDates = groupedElements.map { it.date }.distinct()
+//            val newDates = groupedElements.map { it.date }.distinct()
-
+//
-            // Update the date count stored in this fragment
+//            // Update the date count stored in this fragment
-            dateSize = newDates.size
+//            dateSize = newDates.size
-
+//
-            // Update the item list in the view pager's adapter
+//            // Update the item list in the view pager's adapter
-            viewPagerAdapter.setNewItems(groupedElements, dateSize)
+////            viewPagerAdapter.setNewItems(groupedElements, dateSize)
-
+//
-            // Set the text for the opening hours dialogue
+//            // Set the text for the opening hours dialogue
-            openingHours = viewModel.getCanteenOpeningHours()
+//            openingHours = viewModel.getCanteenOpeningHours()
-
+//
-            binding.swipeRefreshLayout.isRefreshing = false
+//            binding.swipeRefreshLayout.isRefreshing = false
-
+//
-            // Create and attach the tab layout for the ViewPager
+//            // Create and attach the tab layout for the ViewPager
-            createTabLayoutMediator(newDates)
+//            createTabLayoutMediator(newDates)
-        }
+//        }
 
         // Set up functions for when the user swipes to refresh the view
         binding.swipeRefreshLayout.setOnRefreshListener {
@@ -223,7 +222,8 @@ class CanteenFragment : AppFragment(), CanteenOfferItemAdapter.OnClickListener {
         viewModel.setPreference(pref, newValue)
 
         // Update the view
-        viewPagerAdapter.setNewItems(elements.groupElements().distinct(), dateSize)
+        viewModel.registerDietaryPreferencesUpdate()
+//        viewPagerAdapter.setNewItems(elements.groupElements().distinct(), dateSize)
     }
 
     /**
@@ -235,97 +235,6 @@ class CanteenFragment : AppFragment(), CanteenOfferItemAdapter.OnClickListener {
     private fun getPreference(pref: DietaryPreferences): Boolean =
         viewModel.getPreference(pref)
 
-    /**
-     * Retrieves the user's dietary preferences and compiles them into a regular expression that can
-     * be used to filter out items that don't fulfil the preferences. Example:
-     * .......t..|........t.
-     * This will retrieve all items that marked as either vegetarian or vegan
-     * *
-     * @return  regular expression object reflecting the user's preferences
-     */
-    private fun getPrefRegex(): Regex {
-        // Retrieve the user's dietary preference as a string
-        val prefs = viewModel.getDietaryPrefs().deconstruct()
-
-        // Return the 'empty' template string if no preference has been set or found
-        return if (prefs == emptyPreferenceRegex) {
-            Regex(emptyPreferenceRegex)
-        } else {
-            // Create the variable to insert the regular expression into
-            var regexString = ""
-
-            // Create the object to store which preferences need to be met
-            val indices = mutableListOf<Int>()
-
-            // Find all preferences that need to be met
-            prefs.forEachIndexed { index, c ->
-                if (c == DietaryPreferences.C_TRUE) indices.add(index)
-            }
-
-            // Needs to be set to correctly assemble the regular expression
-            var isFirst = true
-
-            // Iterate through every preference that has been set
-            indices.forEach { index ->
-                // Set an OR if more than one preference needs to be met
-                if (!isFirst) regexString += '|'
-
-                // Add the expression looking for the single preference to the entire string
-                regexString += emptyPreferenceRegex.substring(0 until index) +
-                        DietaryPreferences.C_TRUE +
-                        emptyPreferenceRegex.substring(index+1)
-
-                // Ensure that OR statements will be placed between the individual expressions
-                isFirst = false
-            }
-
-            // Compile the string to a regular expression object
-            Regex(regexString)
-        }
-    }
-
-    /**
-     * Groups [CanteenOffer] elements by their categories into [CanteenOfferGroup] elements and
-     * filters for the user's dietary preferences.
-     *
-     * @return  the grouped and filtered elements
-     */
-    private fun List<CanteenOffer>.groupElements(): List<CanteenOfferGroup> {
-        // Get dietary preference regex
-        val prefsRegex = getPrefRegex()
-
-        val filteredForPrefs = if (prefsRegex.toString() == emptyPreferenceRegex) {
-            // Show all elements and skip filtering if no preference is set
-            this
-        } else {
-            // Filter for dietary preferences
-            this.filter {
-                prefsRegex.matches(it.dietaryPreferences)
-            }
-        }
-
-        return filteredForPrefs.map { (_, date, dateId, category, _, canteen, _, _, _, _, _) ->
-            // Create new group elements to group the already filtered elements by their categories
-            CanteenOfferGroup(
-                date,
-                dateId,
-                category,
-                canteen,
-                filteredForPrefs.filter {
-                    it.category == category && it.date == date && it.canteen == canteen
-                }.map {
-                    // Map the individual items to their respective groups
-                    CanteenOfferGroupElement(
-                        it.title,
-                        it.price,
-                        it.dietaryPreferences,
-                        it.allergens
-                    )
-                }
-            )
-        }
-    }
-
     /**
      * Retrieves the localised string for the canteen selected by the user.
      *
@@ -370,17 +279,17 @@ class CanteenFragment : AppFragment(), CanteenOfferItemAdapter.OnClickListener {
      *
      * @param offer item that has been clicked
      */
-    override fun onClick(offer: CanteenOfferGroupElement, category: String) {
+//    override fun onClick(offer: CanteenOfferGroupElement, category: String) {
-        openBottomSheet(AllergenSheet(offer, category))
+//        openBottomSheet(AllergenSheet(offer, category))
-    }
+//    }
-
+//
-    /**
+//    /**
-     * Executed when an item has been long-pressed.
+//     * Executed when an item has been long-pressed.
-     *
+//     *
-     * @param offer item that has been long-pressed
+//     * @param offer item that has been long-pressed
-     * @return      whether the long press was successful
+//     * @return      whether the long press was successful
-     */
+//     */
-    override fun onLongClick(offer: CanteenOfferGroupElement): Boolean {
+//    override fun onLongClick(offer: CanteenOfferGroupElement): Boolean {
-        return false
+//        return false
-    }
+//    }
 }

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

@@ -4,28 +4,27 @@ 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.CanteenOfferItemAdapter
 import com.denizk0461.studip.adapter.StudIPEventPageAdapter
 import com.denizk0461.studip.databinding.RecyclerViewBinding
+import com.denizk0461.studip.model.CanteenOffer
 import com.denizk0461.studip.model.CanteenOfferGroup
+import com.denizk0461.studip.model.CanteenOfferGroupElement
+import com.denizk0461.studip.model.DietaryPreferences
+import com.denizk0461.studip.sheet.AllergenSheet
+import com.denizk0461.studip.viewmodel.CanteenPageViewModel
 
 /**
  * Fragment that is instantiated by [StudIPEventPageAdapter] to display individual days' pages and
  * their events.
  *
- * @param offers            all offers for a given canteen, grouped by category (not filtered by day at
+ * @param currentDay    day to display
- *                          this point)
- * @param onClickListener   for managing click and long press events
- * @param displayAllergens  whether the user wants allergens to be marked
- * @param currentDay        current day
  */
 class CanteenPageFragment(
-    private var offers: List<CanteenOfferGroup>,
-    private val onClickListener: CanteenOfferItemAdapter.OnClickListener,
-    private val displayAllergens: Boolean,
     private val currentDay: Int,
-) : AppFragment() {
+) : AppFragment(), CanteenOfferItemAdapter.OnClickListener {
 
     // Nullable view binding reference
     private var _binding: RecyclerViewBinding? = null
@@ -36,6 +35,13 @@ class CanteenPageFragment(
      */
     private val binding get() = _binding!!
 
+    // View model reference for providing access to the database
+    private val viewModel: CanteenPageViewModel by viewModels()
+
+    private lateinit var recyclerViewAdapter: CanteenOfferItemAdapter
+
+    private val offerList: MutableList<CanteenOffer> = mutableListOf()
+
     // Instantiate the view binding
     override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View {
         _binding = RecyclerViewBinding.inflate(inflater, container, false)
@@ -45,6 +51,11 @@ class CanteenPageFragment(
     override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
         super.onViewCreated(view, savedInstanceState)
 
+        recyclerViewAdapter = CanteenOfferItemAdapter(
+            this,
+            viewModel.preferenceAllergen,
+        )
+
         binding.recyclerView.apply {
             // Set page to scroll vertically
             layoutManager = LinearLayoutManager(
@@ -56,16 +67,141 @@ class CanteenPageFragment(
              * by the newly created adapter (0 = Monday, 4 = Friday)
              * TODO check if the filtered list is empty, and tell the user if it is
              */
-            val o = offers.filter { it.dateId == currentDay }
+//            val o = offers.filter { it.dateId == currentDay }
 
-            adapter = CanteenOfferItemAdapter(
+            adapter = recyclerViewAdapter
-                o,
-                onClickListener,
-                displayAllergens,
-            )
 
             // Animate creation of new page
             scheduleLayoutAnimation()
+
+            viewModel.getOffersByDay(currentDay).observe(viewLifecycleOwner) { offers ->
+                offerList.clear()
+                offerList.addAll(offers)
+                recyclerViewAdapter.setNewData(offers.filterElements().groupElements().distinct())
+//                filterList()
             }
         }
+
+        viewModel.dietaryPreferencesUpdate.observe(viewLifecycleOwner) {
+            filterList()
+        }
+    }
+
+    private fun filterList() {
+        recyclerViewAdapter.setNewData(offerList.filterElements().groupElements().distinct())
+    }
+
+    /**
+     * Groups [CanteenOffer] elements by their categories into [CanteenOfferGroup] elements and
+     * filters for the user's dietary preferences.
+     *
+     * @return  the grouped and filtered elements
+     */
+    private fun List<CanteenOffer>.groupElements(): List<CanteenOfferGroup> {
+
+        return map { (_, date, dateId, category, _, canteen, _, _, _, _, _) ->
+            // Create new group elements to group the already filtered elements by their categories
+            CanteenOfferGroup(
+                date,
+                dateId,
+                category,
+                canteen,
+                filter {
+                    it.category == category && it.date == date && it.canteen == canteen
+                }.map {
+                    // Map the individual items to their respective groups
+                    CanteenOfferGroupElement(
+                        it.title,
+                        it.price,
+                        it.dietaryPreferences,
+                        it.allergens
+                    )
+                }
+            )
+        }
+    }
+
+    private fun List<CanteenOffer>.filterElements(): List<CanteenOffer> {
+
+        // Get dietary preference regex
+        val prefsRegex = getPrefRegex()
+
+        return if (prefsRegex.toString() == DietaryPreferences.TEMPLATE_EMPTY) {
+            // Show all elements and skip filtering if no preference is set
+            this
+        } else {
+            // Filter for dietary preferences
+            this.filter {
+                prefsRegex.matches(it.dietaryPreferences)
+            }
+        }
+    }
+
+    /**
+     * Retrieves the user's dietary preferences and compiles them into a regular expression that can
+     * be used to filter out items that don't fulfil the preferences. Example:
+     * .......t..|........t.
+     * This will retrieve all items that marked as either vegetarian or vegan
+     * *
+     * @return  regular expression object reflecting the user's preferences
+     */
+    private fun getPrefRegex(): Regex {
+        // Retrieve the user's dietary preference as a string
+        val prefs = viewModel.getDietaryPrefs().deconstruct()
+
+        // Return the 'empty' template string if no preference has been set or found
+        return if (prefs == DietaryPreferences.TEMPLATE_EMPTY) {
+            Regex(DietaryPreferences.TEMPLATE_EMPTY)
+        } else {
+            // Create the variable to insert the regular expression into
+            var regexString = ""
+
+            // Create the object to store which preferences need to be met
+            val indices = mutableListOf<Int>()
+
+            // Find all preferences that need to be met
+            prefs.forEachIndexed { index, c ->
+                if (c == DietaryPreferences.C_TRUE) indices.add(index)
+            }
+
+            // Needs to be set to correctly assemble the regular expression
+            var isFirst = true
+
+            // Iterate through every preference that has been set
+            indices.forEach { index ->
+                // Set an OR if more than one preference needs to be met
+                if (!isFirst) regexString += '|'
+
+                // Add the expression looking for the single preference to the entire string
+                regexString += DietaryPreferences.TEMPLATE_EMPTY.substring(0 until index) +
+                        DietaryPreferences.C_TRUE +
+                        DietaryPreferences.TEMPLATE_EMPTY.substring(index+1)
+
+                // Ensure that OR statements will be placed between the individual expressions
+                isFirst = false
+            }
+
+            // Compile the string to a regular expression object
+            Regex(regexString)
+        }
+    }
+
+    /**
+     * Executed when an item has been clicked.
+     *
+     * @param offer item that has been clicked
+     */
+    override fun onClick(offer: CanteenOfferGroupElement, category: String) {
+        openBottomSheet(AllergenSheet(offer, category))
+    }
+
+    /**
+     * Executed when an item has been long-pressed.
+     *
+     * @param offer item that has been long-pressed
+     * @return      whether the long press was successful
+     */
+    override fun onLongClick(offer: CanteenOfferGroupElement): Boolean {
+        return false
+    }
 }

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

@@ -137,6 +137,8 @@ enum class DietaryPreferences(val value: String) {
          */
         const val C_FALSE: Char = '.'
 
+        const val TEMPLATE_EMPTY: String = ".........."
+
         /**
          * Constructs a DietaryPrefObject from a regex string. String must be 10 characters long.
          * A char equal to C_TRUE is treated as a true boolean value. Any other char is treated as a

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

@@ -0,0 +1,33 @@
+package com.denizk0461.studip.viewmodel
+
+import android.app.Application
+import androidx.lifecycle.LiveData
+import com.denizk0461.studip.model.CanteenOffer
+import com.denizk0461.studip.model.DietaryPreferences
+import com.denizk0461.studip.model.SettingsPreferences
+
+class CanteenPageViewModel(app: Application) : AppViewModel(app) {
+
+    /**
+     * Retrieves all canteen offers that match given day.
+     *
+     * @return all canteen offers matching the given day exposed through a LiveData object
+     */
+    fun getOffersByDay(day: Int): LiveData<List<CanteenOffer>> =
+        repo.getOffersByDay(day)
+
+    val dietaryPreferencesUpdate: LiveData<Int> = repo.dietaryPreferencesUpdate
+
+    /**
+     * Retrieve the user's dietary preferences.
+     *
+     * @return dietary preferences
+     */
+    fun getDietaryPrefs(): DietaryPreferences.Object = repo.getDietaryPrefsAsObject()
+
+    /**
+     * This value determines whether the user wants to have allergens marked.
+     */
+    val preferenceAllergen: Boolean
+        get() = repo.getBooleanPreference(SettingsPreferences.ALLERGEN, defaultValue = true)
+}

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

@@ -22,12 +22,7 @@ class CanteenViewModel(app: Application) : AppViewModel(app) {
      */
     val allOffers: LiveData<List<CanteenOffer>> = repo.allOffers
 
-    /**
+
-     * Retrieve the user's dietary preferences.
-     *
-     * @return dietary preferences
-     */
-    fun getDietaryPrefs(): DietaryPreferences.Object = repo.getDietaryPrefsAsObject()
 
     /**
      * Retrieves all canteen offer date objects.
@@ -54,6 +49,17 @@ class CanteenViewModel(app: Application) : AppViewModel(app) {
         doAsync { parser.parse(canteen, onRefreshUpdate, onFinish) }
     }
 
+    fun registerDietaryPreferencesUpdate() {
+        repo.dietaryPreferencesUpdate.postValue(repo.dietaryPreferencesUpdate.value?.plus(1))
+    }
+
+    /**
+     * Retrieves the amount of dates represented in the offers stored locally. Can be observed.
+     *
+     * @return  date count as LiveData
+     */
+    fun getDateCount(): LiveData<Int> = repo.getDateCount()
+
     /**
      * Updates a given dietary preference to a new value.
      *