In diesem Tutorial lernen Sie Schritt für Schritt, wie Sie eine verschachtelte RecyclerView erstellen können. Dabei wird ein Recyclerview innerhalb eines anderen Recyclerviews platziert. Jedes Recyclerview muss einen eigenen Adapter haben, um seine Daten zu binden. Jede dieser Ansichten muss auch den Bildlauf entsprechend behandeln.
Schauen Sie sich die Beispiele unten an.
Beispiel 1: Kotlin Android Nested RecyclerView
Hier ist die Demo zu diesem Projekt:
Schritt 1: Projekt erstellen
Beginnen Sie mit der Erstellung eines leeren Android Studio Projekts.
Schritt 2: Abhängigkeiten
Installieren Sie GravitySnapHelper, indem Sie die folgende Implementierungsanweisung in Ihre app/build.gradle-Datei einfügen:
implementation 'com.github.rubensousa:gravitysnaphelper:2.1.0'Schritt 3: Layouts entwerfen
Es gibt drei Layouts für dieses Projekt:
nested_adapter_item.xml
Dies ist das Layout für das Element "innert recyclerview":
<?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="@dimen/item_width"
android:layout_height="@dimen/item_height"
android:layout_margin="4dp"
android:background="@android:color/black"
tools:context=".MainActivity">
<TextView
android:id="@+id/textView"
style="@style/TextAppearance.AppCompat.Title"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:gravity="center"
android:textColor="@android:color/white"
android:textSize="@dimen/item_text_size"
tools:text="0" />
</FrameLayout>(b). nested_adapter_list
Das Layout für das innere Recyclerview. OrientationAwareRecyclerView hinzufügen:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical"
tools:context=".MainActivity">
<TextView
android:id="@+id/nestedTitleTextView"
style="@style/TextAppearance.AppCompat.Title"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="16dp"
android:layout_marginTop="16dp" />
<com.github.rubensousa.gravitysnaphelper.OrientationAwareRecyclerView
android:id="@+id/nestedRecyclerView"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
</LinearLayout>(c). nested_adapter_item.xml
Das Layout für die äußere Recyclerview. Fügen Sie noch einmal die OrientationAwareRecyclerView hinzu:
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">
<com.github.rubensousa.gravitysnaphelper.OrientationAwareRecyclerView
android:id="@+id/recyclerView"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</androidx.constraintlayout.widget.ConstraintLayout>Schritt 4: Datenklasse erstellen
Diese Datenklasse wird unsere Modellklasse sein:
(a). TiledList.kt
data class TitledList(
val title: String,
val texts: MutableList<String>
)Schritt 5: Scroll State Holder erstellen
Erstellen Sie eine Klasse, die den Scroll-Status hält:
ScrollStateHolder.kt
import android.os.Bundle
import android.os.Parcelable
import androidx.recyclerview.widget.RecyclerView
/**
* Persists scroll state for nested RecyclerViews.
*
* 1. Call [saveScrollState] in [RecyclerView.Adapter.onViewRecycled]
* to save the scroll position.
*
* 2. Call [restoreScrollState] in [RecyclerView.Adapter.onBindViewHolder]
* after changing the adapter's contents to restore the scroll position
*/
class ScrollStateHolder(savedInstanceState: Bundle? = null) {
companion object {
const val STATE_BUNDLE = "scroll_state_bundle"
}
/**
* Provides a key that uniquely identifies a RecyclerView
*/
interface ScrollStateKeyProvider {
fun getScrollStateKey(): String?
}
/**
* Persists the [RecyclerView.LayoutManager] states
*/
private val scrollStates = hashMapOf<String, Parcelable>()
/**
* Keeps track of the keys that point to RecyclerViews
* that have new scroll states that should be saved
*/
private val scrolledKeys = mutableSetOf<String>()
init {
savedInstanceState?.getBundle(STATE_BUNDLE)?.let { bundle ->
bundle.keySet().forEach { key ->
bundle.getParcelable<Parcelable>(key)?.let {
scrollStates[key] = it
}
}
}
}
fun setupRecyclerView(recyclerView: RecyclerView, scrollKeyProvider: ScrollStateKeyProvider) {
recyclerView.addOnScrollListener(object : RecyclerView.OnScrollListener() {
override fun onScrollStateChanged(recyclerView: RecyclerView, newState: Int) {
super.onScrollStateChanged(recyclerView, newState)
if (newState == RecyclerView.SCROLL_STATE_IDLE) {
saveScrollState(recyclerView, scrollKeyProvider)
}
}
override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) {
super.onScrolled(recyclerView, dx, dy)
val key = scrollKeyProvider.getScrollStateKey()
if (key != null && dx != 0) {
scrolledKeys.add(key)
}
}
})
}
fun onSaveInstanceState(outState: Bundle) {
val stateBundle = Bundle()
scrollStates.entries.forEach {
stateBundle.putParcelable(it.key, it.value)
}
outState.putBundle(STATE_BUNDLE, stateBundle)
}
fun clearScrollState() {
scrollStates.clear()
scrolledKeys.clear()
}
/**
* Saves this RecyclerView layout state for a given key
*/
fun saveScrollState(
recyclerView: RecyclerView,
scrollKeyProvider: ScrollStateKeyProvider
) {
val key = scrollKeyProvider.getScrollStateKey() ?: return
// Check if we scrolled the RecyclerView for this key
if (scrolledKeys.contains(key)) {
val layoutManager = recyclerView.layoutManager ?: return
layoutManager.onSaveInstanceState()?.let { scrollStates[key] = it }
scrolledKeys.remove(key)
}
}
/**
* Restores this RecyclerView layout state for a given key
*/
fun restoreScrollState(
recyclerView: RecyclerView,
scrollKeyProvider: ScrollStateKeyProvider
) {
val key = scrollKeyProvider.getScrollStateKey() ?: return
val layoutManager = recyclerView.layoutManager ?: return
val savedState = scrollStates[key]
if (savedState != null) {
layoutManager.onRestoreInstanceState(savedState)
} else {
// If we don't have any state for this RecyclerView,
// make sure we reset the scroll position
layoutManager.scrollToPosition(0)
}
// Mark this key as not scrolled since we just restored the state
scrolledKeys.remove(key)
}
}Schritt 6: Erstellen von Adaptern
Es gibt zwei Adapter:
(a). ChildAdapter.kt
Dies ist der Adapter für die innere Recyclerview, oder die verschachtelte Recyclerview:
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.TextView
import androidx.recyclerview.widget.RecyclerView
class ChildAdapter : RecyclerView.Adapter<ChildAdapter.VH>() {
private var items = listOf<String>()
fun setItems(list: List<String>) {
this.items = list
notifyDataSetChanged()
}
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): VH {
return VH(
LayoutInflater.from(parent.context).inflate(
R.layout.nested_adapter_item,
parent,
false
)
)
}
override fun getItemCount(): Int = items.size
override fun onBindViewHolder(holder: VH, position: Int) {
holder.bind(items[position])
}
class VH(view: View) : RecyclerView.ViewHolder(view) {
private val textView: TextView = view.findViewById(R.id.textView)
init {
view.setOnClickListener {
it.isSelected = !it.isSelected
}
}
fun bind(item: String) {
textView.text = item
}
}
}(b). ParentAdapter.kt
Dies ist der Adapter für die äußere oder übergeordnete Recyclerview:
import android.view.Gravity
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.TextView
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.RecyclerView
import com.github.rubensousa.gravitysnaphelper.GravitySnapHelper
class ParentAdapter(private val scrollStateHolder: ScrollStateHolder) :
RecyclerView.Adapter<ParentAdapter.VH>() {
private var items = listOf<TitledList>()
fun setItems(list: List<TitledList>) {
this.items = list
notifyDataSetChanged()
}
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): VH {
val view = LayoutInflater.from(parent.context).inflate(
R.layout.nested_adapter_list,
parent, false
)
val vh = VH(view, scrollStateHolder)
vh.onCreated()
return vh
}
override fun getItemCount(): Int = items.size
override fun onBindViewHolder(holder: VH, position: Int) {
holder.onBound(items[position])
}
override fun onViewRecycled(holder: VH) {
super.onViewRecycled(holder)
holder.onRecycled()
}
override fun onViewDetachedFromWindow(holder: VH) {
super.onViewDetachedFromWindow(holder)
holder.onDetachedFromWindow()
}
class VH(view: View, private val scrollStateHolder: ScrollStateHolder) :
RecyclerView.ViewHolder(view), ScrollStateHolder.ScrollStateKeyProvider {
private val titleTextView: TextView = view.findViewById(R.id.nestedTitleTextView)
private val recyclerView: RecyclerView = view.findViewById(R.id.nestedRecyclerView)
private val layoutManager = LinearLayoutManager(
view.context,
RecyclerView.HORIZONTAL, false
)
private val adapter = ChildAdapter()
private val snapHelper = GravitySnapHelper(Gravity.START)
private var currentItem: TitledList? = null
override fun getScrollStateKey(): String? = currentItem?.title
fun onCreated() {
recyclerView.adapter = adapter
recyclerView.layoutManager = layoutManager
recyclerView.setHasFixedSize(true)
recyclerView.itemAnimator?.changeDuration = 0
snapHelper.attachToRecyclerView(recyclerView)
scrollStateHolder.setupRecyclerView(recyclerView, this)
}
fun onBound(item: TitledList) {
currentItem = item
titleTextView.text = item.title
adapter.setItems(item.texts)
scrollStateHolder.restoreScrollState(recyclerView, this)
}
fun onRecycled() {
scrollStateHolder.saveScrollState(recyclerView, this)
currentItem = null
}
/**
* If we fast scroll while this ViewHolder's RecyclerView is still settling the scroll,
* the view will be detached and won't be snapped correctly
*
* To fix that, we snap again without smooth scrolling.
*/
fun onDetachedFromWindow() {
if (recyclerView.scrollState != RecyclerView.SCROLL_STATE_IDLE) {
snapHelper.findSnapView(layoutManager)?.let {
val snapDistance = snapHelper.calculateDistanceToFinalSnap(layoutManager, it)
if (snapDistance!![0] != 0 || snapDistance[1] != 0) {
recyclerView.scrollBy(snapDistance[0], snapDistance[1])
}
}
}
}
}
}Schritt 7: MainActivity erstellen
Hier ist der Code für die MainActivity
MainActivity.kt
import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.RecyclerView
class MainActivity : AppCompatActivity() {
private lateinit var adapter: ParentAdapter
private lateinit var recyclerView: RecyclerView
private lateinit var scrollStateHolder: ScrollStateHolder
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
recyclerView = findViewById(R.id.recyclerView)
scrollStateHolder = ScrollStateHolder(savedInstanceState)
adapter = ParentAdapter(scrollStateHolder)
recyclerView.adapter = adapter
recyclerView.layoutManager = LinearLayoutManager(this)
loadItems()
}
override fun onSaveInstanceState(outState: Bundle) {
super.onSaveInstanceState(outState)
scrollStateHolder.onSaveInstanceState(outState)
}
private fun loadItems() {
val lists = arrayListOf<TitledList>()
repeat(20) { listIndex ->
val items = arrayListOf<String>()
repeat(30) { itemIndex -> items.add(itemIndex.toString()) }
lists.add(TitledList("List number $listIndex", items))
}
adapter.setItems(lists)
}
}Run
Kopieren Sie den Code oder laden Sie ihn über den unten stehenden Link herunter, erstellen Sie ihn und führen Sie ihn aus.
Referenz
Hier sind die Referenzlinks:
Download Beispiel
