RecyclerView GridLayout Multi Selection With Toolbar

dependencies {
    implementation 'androidx.recyclerview:recyclerview-selection:1.0.0'
    // implementation 'androidx.recyclerview:recyclerview-selection:1.1.0-rc01'
}

class TestSelectionFragment : Fragment() {    private lateinit var adapter: LocalAdapter    private var tracker: SelectionTracker<String>? = null    override fun onCreateView(        inflater: LayoutInflater, container: ViewGroup?,        savedInstanceState: Bundle?    ): View? {        return inflater.inflate(R.layout.testselection, container, false)    }    override fun onActivityCreated(savedInstanceState: Bundle?) {        super.onActivityCreated(savedInstanceState)        // might be necessary under certain circumstances when using Jetpack Navigation        // tracker = null        initSelection()        initList()    }    private fun initSelection() {        selectionToolbar.apply {            inflateMenu(R.menu.selection)            setOnMenuItemClickListener {                when(it.itemId) {                    R.id.action_add_to -> {                        // TODO: do something                        true                    }                    R.id.action_delete -> {                        // TODO: do something                        true                    }                    else -> false                }            }            // use navigationIcon as close icon            navigationIcon = ContextCompat.getDrawable(context, R.drawable.ic_baseline_close_24)            setNavigationOnClickListener {                tracker?.clearSelection()            }        }    }    private fun initList() {        val layoutManager = GridLayoutManager(context, 3)        list.layoutManager = layoutManager        if (!::adapter.isInitialized) {            adapter = LocalAdapter()            // adapter.setHasStableIds(true)        }        list.adapter = adapter        // must set adapter to list before SelectionTracker.Builder, else IllegalArgumentException        val tracker = this.tracker ?: run {            Timber.d("set tracker")            SelectionTracker.Builder<String>(                "photo-selection",                list,                // StableIdKeyProvider(list),                LocalItemKeyProvider(adapter),                LocalItemDetailsLookup(list),                // StorageStrategy.createLongStorage(),                StorageStrategy.createStringStorage()            ).withSelectionPredicate(                // SelectionPredicates.createSelectAnything()                LocalSelectionPredicate(adapter)            ).build().also {                this.tracker = it            }        }        adapter.tracker = tracker        selectionToolbar.isVisible = tracker.hasSelection()        // var lastHasSelection = false        tracker.addObserver(object: SelectionTracker.SelectionObserver<Long>() {            var lastHasSelection = false            override fun onSelectionChanged() {                super.onSelectionChanged()                // this might not be realiable under certain circumstances                // val selectionStateChanged = selectionToolbar.isVisible != tracker.hasSelection()                val selectionStateChanged = lastHasSelection != tracker.hasSelection()                lastHasSelection = tracker.hasSelection()                selectionToolbar.isVisible = tracker.hasSelection()                selectionToolbar.title = tracker.selection.size().toString()                // selection state changed                // if (lastHasSelection != tracker.hasSelection()) {                if (selectionStateChanged) {                    adapter.notifySelectableItemsChanged()                }                // lastHasSelection = tracker.hasSelection()            }        })        val items = mutableListOf<ViewItem>()        for (number in 0..10) {            if (number % 2 == 0) {                val key = "number-$number"                items.add(ViewItem.NumberItem(key))            }            else {                val key = "noselect-$number"                items.add(ViewItem.NotSelectable(key))            }        }        adapter.submitList(items)    }    private class LocalItemDetailsLookup(private val recyclerView: RecyclerView) : ItemDetailsLookup<String>() {        override fun getItemDetails(event: MotionEvent): ItemDetails<String>? {            val view = recyclerView.findChildViewUnder(event.x, event.y)            if (view != null) {                return (recyclerView.getChildViewHolder(view) as LocalAdapter.ViewHolder)                    .getItemDetails()            }            return null        }    }    private class LocalSelectionPredicate(private val adapter: LocalAdapter): SelectionTracker.SelectionPredicate<String>() {        override fun canSelectMultiple(): Boolean {            return true        }        override fun canSetStateForKey(key: String, nextState: Boolean): Boolean {            val item = adapter.currentList.find { it.id == key }            return item is ViewItem.NumberItem        }        override fun canSetStateAtPosition(position: Int, nextState: Boolean): Boolean {            val item = adapter.currentList[position]            return item is ViewItem.NumberItem        }    }    private class LocalItemKeyProvider(private val adapter: LocalAdapter) : ItemKeyProvider<String>(ItemKeyProvider.SCOPE_MAPPED) {        override fun getKey(position: Int): String {            return adapter.currentList[position].id        }        override fun getPosition(key: String): Int {            //  RecyclerView.NO_POSITION = -1            return adapter.currentList.indexOfFirst { it.id == key }        }    }    sealed class ViewItem(open val id: String, val resource: Int) {        data class NumberItem(override val id: String) : ViewItem(id, R.layout.testselection_item)        data class NotSelectable(override val id: String) : ViewItem(id, R.layout.testselection_static_item)    }    class LocalAdapter() : ListAdapter<ViewItem, LocalAdapter.ViewHolder>(DiffCallback()) {        lateinit var tracker: SelectionTracker<String>        // override fun getItemId(position: Int): Long = position.toLong()        override fun getItemViewType(position: Int): Int {            return getItem(position).resource        }        override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {            val view = LayoutInflater.from(parent.context)                .inflate(viewType, parent, false)            return ViewHolder(view)        }        override fun onBindViewHolder(holder: ViewHolder, position: Int) {            val item = getItem(position)            Timber.d("position=$position, selected=${tracker.isSelected(item.id)}, selection=${tracker.selection}")            holder.bind(getItem(position), tracker.isSelected(item.id))        }        fun notifySelectableItemsChanged() {            for (index in 0 until itemCount) {                val item = getItem(index)                if (item is ViewItem.NumberItem)                    notifyItemChanged(index)            }        }        private class DiffCallback: DiffUtil.ItemCallback<ViewItem>() {            override fun areItemsTheSame(oldItem: ViewItem, newItem: ViewItem): Boolean {                if (oldItem.resource != newItem.resource) return false                // check if id is the same                return oldItem.id == newItem.id            }            @SuppressLint("DiffUtilEquals")            override fun areContentsTheSame(oldItem: ViewItem, newItem: ViewItem): Boolean {                // check if content is the same                // equals using data class                return oldItem == newItem            }        }        inner class ViewHolder(override val containerView: View) : RecyclerView.ViewHolder(containerView),            LayoutContainer {            // why update ui here? easier to access view without need to holder.titleTextView            fun bind(item: ViewItem, isSelected: Boolean) {                when(item) {                    is ViewItem.NumberItem -> {                        numberTextView.text = item.id                        val res = if (isSelected) R.drawable.ic_baseline_check_circle_24 else R.drawable.ic_baseline_radio_button_unchecked_24                        selectionImageView.setImageResource(res)                        selectionImageView.isVisible = tracker.hasSelection()                    }                }            }            fun getItemDetails(): ItemDetailsLookup.ItemDetails<String> =                object : ItemDetailsLookup.ItemDetails<String>() {                    override fun getPosition(): Int = adapterPosition                    override fun getSelectionKey(): String? = getItem(adapterPosition).id                }        }    }}

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    tools:context="com.luasoftware.garden.view.TestSelectionFragment"  
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <androidx.appcompat.widget.Toolbar
        android:id="@+id/selectionToolbar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:visibility="gone"
        tools:visibility="visible"
        />

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/list"
        app:layoutManager="androidx.recyclerview.widget.GridLayoutManager"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1" />
</LinearLayout>

<?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"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    xmlns:tools="http://schemas.android.com/tools"
    tools:layout_height="500dp">

    <TextView
        android:id="@+id/numberTextView"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:gravity="center"
        app:layout_constraintDimensionRatio="H,1:1"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:text="Test">

    </TextView>


    <ImageView
        android:id="@+id/selectionImageView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="8dp"
        android:src="@drawable/ic_baseline_radio_button_unchecked_24"
        android:tint="@android:color/black"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintEnd_toEndOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>

<?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"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    xmlns:tools="http://schemas.android.com/tools"
    tools:layout_height="500dp">

    <TextView
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:gravity="center"
        app:layout_constraintDimensionRatio="H,1:1"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        android:text="NO SELECT">
    </TextView>
    
</androidx.constraintlayout.widget.ConstraintLayout>

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">
    <item
        android:id="@+id/action_add_to"
        android:icon="@drawable/ic_baseline_add_24"
        app:iconTint="@color/selection_icon_active"
        android:title="Add to"
        app:showAsAction="always"
        />

    <item
        android:id="@+id/action_delete"
        android:icon="@drawable/ic_baseline_delete_24"
        app:iconTint="@color/selection_icon_active"
        android:title="Delete"
        app:showAsAction="always"
        />
</menu>