refactor MultiChoiceHelper to allow changing its underlying adapter

app/src/main/java/be/digitalia/fosdem/adapters/BookmarksAdapter.kt

@@ -1,5 +1,6 @@
 package be.digitalia.fosdem.adapters
 
+import android.content.Context
 import android.content.Intent
 import android.graphics.Typeface
 import android.text.SpannableString
@@ -10,16 +11,15 @@ import android.view.View
 import android.view.ViewGroup
 import android.widget.TextView
 import androidx.annotation.ColorInt
-import androidx.appcompat.app.AppCompatActivity
 import androidx.collection.SimpleArrayMap
 import androidx.core.content.ContextCompat
 import androidx.core.text.set
 import androidx.core.view.isGone
+import androidx.lifecycle.LifecycleOwner
 import androidx.lifecycle.observe
 import androidx.recyclerview.widget.ListAdapter
 import androidx.recyclerview.widget.RecyclerView
 import androidx.recyclerview.widget.RecyclerView.AdapterDataObserver
-import androidx.savedstate.SavedStateRegistryOwner
 import be.digitalia.fosdem.R
 import be.digitalia.fosdem.activities.EventDetailsActivity
 import be.digitalia.fosdem.api.FosdemApi
@@ -29,11 +29,12 @@ import be.digitalia.fosdem.utils.DateUtils
 import be.digitalia.fosdem.widgets.MultiChoiceHelper
 import java.text.DateFormat
 
-class BookmarksAdapter(activity: AppCompatActivity, owner: SavedStateRegistryOwner,
+class BookmarksAdapter(context: Context, owner: LifecycleOwner,
-                       multiChoiceModeListener: MultiChoiceHelper.MultiChoiceModeListener? = null)
+                       private val multiChoiceHelper: MultiChoiceHelper)
     : ListAdapter<Event, BookmarksAdapter.ViewHolder>(DIFF_CALLBACK) {
 
-    private val timeDateFormat = DateUtils.getTimeDateFormat(activity)
+    private val timeDateFormat = DateUtils.getTimeDateFormat(context)
+
     @ColorInt
     private val errorColor: Int
     private val observers = SimpleArrayMap<AdapterDataObserver, BookmarksDataObserverWrapper>()
@@ -41,20 +42,16 @@ class BookmarksAdapter(activity: AppCompatActivity, owner: SavedStateRegistryOwn
 
     init {
         setHasStableIds(true)
-        with(activity.theme.obtainStyledAttributes(R.styleable.ErrorColors)) {
+        with(context.theme.obtainStyledAttributes(R.styleable.ErrorColors)) {
             errorColor = getColor(R.styleable.ErrorColors_colorError, 0)
             recycle()
         }
-        FosdemApi.getRoomStatuses(activity).observe(owner) { statuses ->
+        FosdemApi.getRoomStatuses(context).observe(owner) { statuses ->
             roomStatuses = statuses
             notifyItemRangeChanged(0, itemCount, DETAILS_PAYLOAD)
         }
     }
 
-    val multiChoiceHelper = MultiChoiceHelper(activity, owner, this).apply {
-        setMultiChoiceModeListener(multiChoiceModeListener)
-    }
-
     override fun getItemId(position: Int) = getItem(position).id
 
     override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {

app/src/main/java/be/digitalia/fosdem/fragments/BookmarksListFragment.kt

@@ -32,8 +32,8 @@ import be.digitalia.fosdem.widgets.MultiChoiceHelper
 class BookmarksListFragment : RecyclerViewFragment(), CreateNfcAppDataCallback {
 
     private val viewModel: BookmarksViewModel by viewModels()
-    private val adapter: BookmarksAdapter by lazy(LazyThreadSafetyMode.NONE) {
+    private val multiChoiceHelper: MultiChoiceHelper by lazy(LazyThreadSafetyMode.NONE) {
-        val multiChoiceModeListener = object : MultiChoiceHelper.MultiChoiceModeListener {
+        MultiChoiceHelper(requireActivity() as AppCompatActivity, this, object : MultiChoiceHelper.MultiChoiceModeListener {
 
             override fun onCreateActionMode(mode: ActionMode, menu: Menu): Boolean {
                 mode.menuInflater.inflate(R.menu.action_mode_bookmarks, menu)
@@ -41,7 +41,7 @@ class BookmarksListFragment : RecyclerViewFragment(), CreateNfcAppDataCallback {
             }
 
             private fun updateSelectedCountDisplay(mode: ActionMode) {
-                val count = adapter.multiChoiceHelper.checkedItemCount
+                val count = multiChoiceHelper.checkedItemCount
                 mode.title = resources.getQuantityString(R.plurals.selected, count, count)
             }
 
@@ -53,7 +53,7 @@ class BookmarksListFragment : RecyclerViewFragment(), CreateNfcAppDataCallback {
             override fun onActionItemClicked(mode: ActionMode, item: MenuItem) = when (item.itemId) {
                 R.id.delete -> {
                     // Remove multiple bookmarks at once
-                    viewModel.removeBookmarks(adapter.multiChoiceHelper.checkedItemIds)
+                    viewModel.removeBookmarks(multiChoiceHelper.checkedItemIds)
                     mode.finish()
                     true
                 }
@@ -65,9 +65,10 @@ class BookmarksListFragment : RecyclerViewFragment(), CreateNfcAppDataCallback {
             }
 
             override fun onDestroyActionMode(mode: ActionMode) {}
+        })
     }
-
+    private val adapter by lazy(LazyThreadSafetyMode.NONE) {
-        BookmarksAdapter((requireActivity() as AppCompatActivity), this, multiChoiceModeListener)
+        BookmarksAdapter(requireContext(), this, multiChoiceHelper)
     }
     private var filterMenuItem: MenuItem? = null
     private var upcomingOnlyMenuItem: MenuItem? = null
@@ -95,6 +96,7 @@ class BookmarksListFragment : RecyclerViewFragment(), CreateNfcAppDataCallback {
 
         viewModel.bookmarks.observe(viewLifecycleOwner) { bookmarks ->
             adapter.submitList(bookmarks)
+            multiChoiceHelper.setAdapter(adapter, this)
             isProgressBarVisible = false
         }
     }

app/src/main/java/be/digitalia/fosdem/utils/Parcelers.kt

@@ -17,30 +17,24 @@ object DateParceler : Parceler<Date?> {
     override fun Date?.write(parcel: Parcel, flags: Int) = parcel.writeLong(this?.time ?: -1L)
 }
 
-object IntLongSparseArrayParceler : Parceler<LongSparseArray<Int>?> {
+object IntLongSparseArrayParceler : Parceler<LongSparseArray<Int>> {
 
-    override fun create(parcel: Parcel): LongSparseArray<Int>? {
+    override fun create(parcel: Parcel): LongSparseArray<Int> {
         val size = parcel.readInt()
-        return if (size >= 0) {
+        return LongSparseArray<Int>(size).apply {
-            LongSparseArray<Int>(size).apply {
             for (i in 0 until size) {
                 val key = parcel.readLong()
                 val value = parcel.readInt()
                 append(key, value)
             }
         }
-        } else null
     }
 
-    override fun LongSparseArray<Int>?.write(parcel: Parcel, flags: Int) {
+    override fun LongSparseArray<Int>.write(parcel: Parcel, flags: Int) {
-        if (this == null) {
-            parcel.writeInt(-1)
-        } else {
         parcel.writeInt(size)
         forEach { key, value ->
             parcel.writeLong(key)
             parcel.writeInt(value)
         }
     }
-    }
 }

app/src/main/java/be/digitalia/fosdem/widgets/MultiChoiceHelper.kt

@@ -11,6 +11,7 @@ import androidx.appcompat.view.ActionMode
 import androidx.core.util.set
 import androidx.core.util.size
 import androidx.lifecycle.DefaultLifecycleObserver
+import androidx.lifecycle.Lifecycle
 import androidx.lifecycle.LifecycleOwner
 import androidx.recyclerview.widget.RecyclerView
 import androidx.recyclerview.widget.RecyclerView.AdapterDataObserver
@@ -21,13 +22,11 @@ import kotlinx.android.parcel.WriteWith
 
 /**
  * Helper class to reproduce ListView's modal MultiChoice mode with a RecyclerView.
- * Declare and use this class from inside your Adapter.
+ * Call setAdapter(adapter, adapterLifecycleOwner) on it as soon as the adapter data is populated.
  *
  * @author Christophe Beyls
  */
-class MultiChoiceHelper(private val activity: AppCompatActivity,
+class MultiChoiceHelper(private val activity: AppCompatActivity, owner: SavedStateRegistryOwner, listener: MultiChoiceModeListener) {
-                        owner: SavedStateRegistryOwner,
-                        private val adapter: RecyclerView.Adapter<*>) {
     /**
      * A handy ViewHolder base class which works with the MultiChoiceHelper
      * and reproduces the default behavior of a ListView.
@@ -84,7 +83,7 @@ class MultiChoiceHelper(private val activity: AppCompatActivity,
         /**
          * Called when an item is checked or unchecked during selection mode.
          *
-         * @param mode     The [ActionMode] providing the selection startSupportActionModemode
+         * @param mode     The [ActionMode] providing the selection mode
          * @param position Adapter position of the item that was checked or unchecked
          * @param id       Adapter ID of the item that was checked or unchecked
          * @param checked  `true` if the item is now checked, `false`
@@ -93,11 +92,14 @@ class MultiChoiceHelper(private val activity: AppCompatActivity,
         fun onItemCheckedStateChanged(mode: ActionMode, position: Int, id: Long, checked: Boolean)
     }
 
+    private val multiChoiceModeCallback: MultiChoiceModeListener = MultiChoiceModeWrapper(listener)
     val checkedItemPositions: SparseBooleanArray
-    private val checkedIdStates: LongSparseArray<Int>?
+    private val checkedIdStates: LongSparseArray<Int>
     var checkedItemCount: Int
         private set
-    private var multiChoiceModeCallback: MultiChoiceModeWrapper? = null
+    var adapter: RecyclerView.Adapter<*>? = null
+        private set
+    private var adapterLifecycle: Lifecycle? = null
     private var choiceActionMode: ActionMode? = null
 
     /**
@@ -105,36 +107,66 @@ class MultiChoiceHelper(private val activity: AppCompatActivity,
      * so this class will be notified before the RecyclerView in case of data set changes.
      */
     init {
-        adapter.registerAdapterDataObserver(AdapterDataSetObserver())
         val restoreBundle = owner.savedStateRegistry.consumeRestoredStateForKey(STATE_KEY)
         if (restoreBundle == null) {
             checkedItemCount = 0
             checkedItemPositions = SparseBooleanArray(0)
-            checkedIdStates = if (adapter.hasStableIds()) LongSparseArray(0) else null
+            checkedIdStates = LongSparseArray(0)
         } else {
             val savedState: SavedState = restoreBundle.getParcelable(PARCELABLE_KEY)!!
             checkedItemCount = savedState.checkedItemCount
             checkedItemPositions = savedState.checkedItemPositions
             checkedIdStates = savedState.checkedIdStates
-            // Try early restoration, otherwise do it when items are inserted
-            if (adapter.itemCount > 0) {
-                onAdapterPopulated()
-            }
         }
         owner.savedStateRegistry.registerSavedStateProvider(STATE_KEY) {
             Bundle(1).apply {
-                putParcelable(PARCELABLE_KEY, SavedState(checkedItemCount, checkedItemPositions.clone(), checkedIdStates?.clone()))
+                putParcelable(PARCELABLE_KEY, SavedState(checkedItemCount, checkedItemPositions.clone(), checkedIdStates.clone()))
             }
         }
-        owner.lifecycle.addObserver(object : DefaultLifecycleObserver {
-            override fun onDestroy(owner: LifecycleOwner) {
-                clearChoices()
-            }
-        })
     }
 
-    fun setMultiChoiceModeListener(listener: MultiChoiceModeListener?) {
+    private val adapterDataSetObserver = object : AdapterDataObserver() {
-        multiChoiceModeCallback = if (listener == null) null else MultiChoiceModeWrapper(listener)
+        override fun onChanged() {
+            confirmCheckedPositions()
+        }
+
+        override fun onItemRangeInserted(positionStart: Int, itemCount: Int) {
+            confirmCheckedPositions()
+        }
+
+        override fun onItemRangeMoved(fromPosition: Int, toPosition: Int, itemCount: Int) {
+            confirmCheckedPositions()
+        }
+
+        override fun onItemRangeRemoved(positionStart: Int, itemCount: Int) {
+            confirmCheckedPositions()
+        }
+    }
+
+    private val adapterLifecycleObserver = object : DefaultLifecycleObserver {
+        override fun onDestroy(owner: LifecycleOwner) {
+            adapter = null
+            adapterLifecycle = null
+            choiceActionMode?.finish()
+        }
+    }
+
+    fun setAdapter(adapter: RecyclerView.Adapter<*>, adapterLifecycleOwner: LifecycleOwner) {
+        if (this.adapter !== adapter) {
+            this.adapter?.unregisterAdapterDataObserver(adapterDataSetObserver)
+            this.adapterLifecycle?.removeObserver(adapterLifecycleObserver)
+            this.adapter = adapter
+            this.adapterLifecycle = adapterLifecycleOwner.lifecycle
+            adapter.registerAdapterDataObserver(adapterDataSetObserver)
+            adapterLifecycleOwner.lifecycle.addObserver(adapterLifecycleObserver)
+            if (!adapter.hasStableIds()) {
+                checkedIdStates.clear()
+            }
+            confirmCheckedPositions()
+            if (checkedItemCount > 0) {
+                startSupportActionModeIfNeeded()
+            }
+        }
     }
 
     fun isItemChecked(position: Int): Boolean {
@@ -143,7 +175,7 @@ class MultiChoiceHelper(private val activity: AppCompatActivity,
 
     val checkedItemIds: LongArray
         get() {
-            val idStates = checkedIdStates ?: return LongArray(0)
+            val idStates = checkedIdStates
             return LongArray(idStates.size()) { idStates.keyAt(it) }
         }
 
@@ -152,10 +184,10 @@ class MultiChoiceHelper(private val activity: AppCompatActivity,
             val start = checkedItemPositions.keyAt(0)
             val end = checkedItemPositions.keyAt(checkedItemPositions.size() - 1)
             checkedItemPositions.clear()
-            checkedIdStates?.clear()
+            checkedIdStates.clear()
             checkedItemCount = 0
 
-            adapter.notifyItemRangeChanged(start, end - start + 1, SELECTION_PAYLOAD)
+            adapter?.notifyItemRangeChanged(start, end - start + 1, SELECTION_PAYLOAD)
 
             choiceActionMode?.finish()
         }
@@ -171,9 +203,9 @@ class MultiChoiceHelper(private val activity: AppCompatActivity,
         checkedItemPositions[position] = value
 
         if (oldValue != value) {
-            val id = adapter.getItemId(position)
+            val id = adapter?.getItemId(position) ?: RecyclerView.NO_ID
 
-            if (checkedIdStates != null) {
+            if (adapter?.hasStableIds() == true) {
                 if (value) {
                     checkedIdStates[id] = position
                 } else {
@@ -187,13 +219,12 @@ class MultiChoiceHelper(private val activity: AppCompatActivity,
                 checkedItemCount--
             }
 
-            adapter.notifyItemChanged(position, SELECTION_PAYLOAD)
+            adapter?.notifyItemChanged(position, SELECTION_PAYLOAD)
 
-            val actionMode = choiceActionMode
+            choiceActionMode?.let {
-            if (actionMode != null) {
+                multiChoiceModeCallback.onItemCheckedStateChanged(it, position, id, value)
-                multiChoiceModeCallback?.onItemCheckedStateChanged(actionMode, position, id, value)
                 if (checkedItemCount == 0) {
-                    actionMode.finish()
+                    it.finish()
                 }
             }
         }
@@ -203,21 +234,14 @@ class MultiChoiceHelper(private val activity: AppCompatActivity,
         setItemChecked(position, !isItemChecked(position))
     }
 
-    private fun onAdapterPopulated() {
-        confirmCheckedPositions()
-        if (checkedItemCount > 0) {
-            startSupportActionModeIfNeeded()
-        }
-    }
-
     private fun startSupportActionModeIfNeeded() {
         if (choiceActionMode == null) {
-            val callback = checkNotNull(multiChoiceModeCallback) { "No callback set" }
+            choiceActionMode = activity.startSupportActionMode(multiChoiceModeCallback)
-            choiceActionMode = activity.startSupportActionMode(callback)
         }
     }
 
     fun confirmCheckedPositions() {
+        val adapter = this.adapter ?: return
         if (checkedItemCount == 0) {
             return
         }
@@ -228,10 +252,10 @@ class MultiChoiceHelper(private val activity: AppCompatActivity,
         if (itemCount == 0) {
             // Optimized path for empty adapter: remove all items.
             checkedItemPositions.clear()
-            checkedIdStates?.clear()
+            checkedIdStates.clear()
             checkedItemCount = 0
             checkedCountChanged = true
-        } else if (checkedIdStates != null) {
+        } else if (adapter.hasStableIds()) {
             // Clear out the positional check states, we'll rebuild it below from IDs.
             checkedItemPositions.clear()
 
@@ -260,10 +284,7 @@ class MultiChoiceHelper(private val activity: AppCompatActivity,
                         checkedIndex--
                         checkedItemCount--
                         checkedCountChanged = true
-                        val actionMode = choiceActionMode
+                        choiceActionMode?.let { multiChoiceModeCallback.onItemCheckedStateChanged(it, lastPos, id, false) }
-                        if (actionMode != null) {
-                            multiChoiceModeCallback?.onItemCheckedStateChanged(actionMode, lastPos, id, false)
-                        }
                     }
                 } else {
                     checkedItemPositions[lastPos] = true
@@ -285,12 +306,11 @@ class MultiChoiceHelper(private val activity: AppCompatActivity,
             }
         }
 
-        val actionMode = choiceActionMode
+        if (checkedCountChanged) {
-        if (checkedCountChanged && actionMode != null) {
             if (checkedItemCount == 0) {
-                actionMode.finish()
+                choiceActionMode?.finish()
             } else {
-                actionMode.invalidate()
+                choiceActionMode?.invalidate()
             }
         }
     }
@@ -298,27 +318,7 @@ class MultiChoiceHelper(private val activity: AppCompatActivity,
     @Parcelize
     class SavedState(val checkedItemCount: Int,
                      val checkedItemPositions: SparseBooleanArray,
-                     val checkedIdStates: @WriteWith<IntLongSparseArrayParceler> LongSparseArray<Int>?) : Parcelable
+                     val checkedIdStates: @WriteWith<IntLongSparseArrayParceler> LongSparseArray<Int>) : Parcelable
-
-    private inner class AdapterDataSetObserver : AdapterDataObserver() {
-        override fun onChanged() {
-            confirmCheckedPositions()
-        }
-
-        override fun onItemRangeInserted(positionStart: Int, itemCount: Int) {
-            if (itemCount > 0) {
-                onAdapterPopulated()
-            }
-        }
-
-        override fun onItemRangeMoved(fromPosition: Int, toPosition: Int, itemCount: Int) {
-            confirmCheckedPositions()
-        }
-
-        override fun onItemRangeRemoved(positionStart: Int, itemCount: Int) {
-            confirmCheckedPositions()
-        }
-    }
 
     private inner class MultiChoiceModeWrapper(private val wrapped: MultiChoiceModeListener) : MultiChoiceModeListener by wrapped {