Android RecylerView ListAdapter (Kotlin)
December 22, 2019Why use ListAdapter
It only update items which has changed (with animation shown).
NOTE: Beware of some ListAdapter Caveats.
Fragment
class AlbumListFragment : Fragment() {
private val viewModel by viewModels<AlbumListViewModel>()
private lateinit var adapter: LocalAdapter
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
return inflater.inflate(R.layout.albumlist, container, false)
}
override fun onActivityCreated(savedInstanceState: Bundle?) {
super.onActivityCreated(savedInstanceState)
initList()
}
private fun initList() {
adapter = LocalAdapter(viewModel)
list.adapter = adapter
val items = mutableListOf<ViewItem>()
// TODO: load items
adapter.submitList(items)
}
sealed class ViewItem(open val id: String, val resource: Int) {
data class AlbumItem(override val id: String, val title: String, val childCount: Int) : ViewItem(id, R.layout.albumlist_item)
}
class LocalAdapter(val viewModel: AlbumListViewModel) : ListAdapter<ViewItem, LocalAdapter.ViewHolder>(DiffCallback()) {
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) {
holder.bind(getItem(position))
}
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) {
when(item) {
is ViewItem.AlbumItem -> {
titleTextView.text = item.title
detailTextView.text = "${item.childCount} items"
}
}
}
}
}
}
NOTE: Refer Handle RecyclerView Click Event With LiveData.
NOTE: Refer Kotlin Android Extentions ViewBinding for RecyclerView ViewHolder (LayoutContainer).
R.layout.albumlist
<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
xmlns:app="http://schemas.android.com/apk/res-auto"
tools:context=".view.AlbumListFragment">
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/list"
app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</FrameLayout>
R.layout.albumlist_item
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:fresco="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_margin="@dimen/margin16"
>
<TextView
android:id="@+id/titleTextView"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="@dimen/margin8"
android:layout_marginBottom="@dimen/margin8"
tools:text="Title" />
<TextView
android:id="@+id/detailTextView"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:textAppearance="@style/TextAppearance.AppCompat.Small"
tools:text="10 items" />
</LinearLayout>
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