feat(reminders): ensure valid deck selected during edits

GSoC 2025: Review Reminders

Currently, if the user tries to edit a review reminder corresponding to a non-existent deck, the deck spinner will become bugged. This change ensures the AddEditReminderDialog always has a valid deck selected. For example, this change means that if the user deletes a deck and goes to check their reminders, quickly clicking and saving the review reminder which is now no longer associated with a deck will cause the review reminder to be reassigned to a valid deck.

Author: ericli3690

AnkiDroid/src/main/java/com/ichi2/anki/reviewreminders/AddEditReminderDialog.kt

@@ -40,9 +40,11 @@ import com.google.android.material.button.MaterialButton
 import com.google.android.material.textfield.TextInputLayout
 import com.google.android.material.timepicker.MaterialTimePicker
 import com.google.android.material.timepicker.TimeFormat
+import com.ichi2.anki.CollectionManager.withCol
 import com.ichi2.anki.DeckSpinnerSelection
 import com.ichi2.anki.R
 import com.ichi2.anki.dialogs.ConfirmationDialog
+import com.ichi2.anki.isDefaultDeckEmpty
 import com.ichi2.anki.launchCatchingTask
 import com.ichi2.anki.libanki.Consts
 import com.ichi2.anki.libanki.DeckId
@@ -192,10 +194,35 @@ class AddEditReminderDialog : DialogFragment() {
         launchCatchingTask {
             Timber.d("Setting up deck spinner")
             deckSpinnerSelection.initializeScheduleRemindersDeckSpinner()
-            deckSpinnerSelection.selectDeckById(viewModel.deckSelected.value ?: Consts.DEFAULT_DECK_ID, setAsCurrentDeck = false)
+            val deckToSelect = ensureValidDeckSelected()
+            deckSpinnerSelection.selectDeckById(deckToSelect, setAsCurrentDeck = false)
         }
     }
 
+    /**
+     * Checks to see if the ViewModel's selected deck is valid and exists. If it does not, we set the selected deck to a
+     * valid deck (either the default deck or "all decks", depending on whether the default deck is present or not).
+     *
+     * @return The valid deck ID that is now selected.
+     */
+    private suspend fun ensureValidDeckSelected(): DeckId {
+        val fallbackSelection = if (isDefaultDeckEmpty()) DeckSpinnerSelection.ALL_DECKS_ID else Consts.DEFAULT_DECK_ID
+        val currentlySelectedDeckID = viewModel.deckSelected.value
+        val deckToSelect =
+            when (currentlySelectedDeckID) {
+                DeckSpinnerSelection.ALL_DECKS_ID -> DeckSpinnerSelection.ALL_DECKS_ID
+                Consts.DEFAULT_DECK_ID -> fallbackSelection
+                null -> fallbackSelection
+                else -> {
+                    val doesDeckExist = withCol { decks.have(currentlySelectedDeckID) }
+                    if (doesDeckExist) currentlySelectedDeckID else fallbackSelection
+                }
+            }
+        viewModel.setDeckSelected(deckToSelect)
+        Timber.d("Initial selected deck ID: %s, newly selected deck ID: %s", currentlySelectedDeckID, deckToSelect)
+        return deckToSelect
+    }
+
     private fun setUpAdvancedDropdown() {
         val advancedDropdown = contentView.findViewById<LinearLayout>(R.id.add_edit_reminder_advanced_dropdown)
         val advancedDropdownIcon = contentView.findViewById<ImageView>(R.id.add_edit_reminder_advanced_dropdown_icon)

AnkiDroid/src/main/java/com/ichi2/anki/reviewreminders/AddEditReminderDialogViewModel.kt

@@ -51,6 +51,12 @@ class AddEditReminderDialogViewModel(
         )
     val time: LiveData<ReviewReminderTime> = _time
 
+    /**
+     * Here, we set an immediate default value for the deck selected based on the dialog mode.
+     * However, it is possible that the deck with this deck ID does not currently exist in the collection
+     * (ex. due to a deleted deck, changed collection folder, etc.). Since checking for this case requires
+     * accessing the collection, we handle it in [AddEditReminderDialog.ensureValidDeckSelected].
+     */
     private val _deckSelected =
         MutableLiveData(
             when (dialogMode) {