如何解决RecyclerView选择与对话框一起导致崩溃空对象上的getAdapterPostion 编辑：
在我当前正在开发的应用程序中，我在viewpager中有一个片段，其中显示了RecyclerView，其中填充了数据库中的一些数据。在此RecyclerView中，我已使用recyclerview-selection库以及一个actionmode实现了ItemSelection。仅此一项就可以了。但是，我还有一个FloatingActionButton，它会打开一个对话框，用户可以在其中向数据库添加新入口，该入口也将显示在recyclerview中。对话框成功打开，但是当用户单击edittext时，它崩溃并显示以下错误消息：
2020-08-16 16:45:36.413 12939-12939/com.nilswinking.kochbuch2 E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.me.myapp,PID: 12939
java.lang.NullPointerException: Attempt to invoke virtual method 'int androidx.recyclerview.widget.RecyclerView$ViewHolder.getAdapterPosition()' on a null object reference
at androidx.recyclerview.selection.StableIdKeyProvider.onDetached(StableIdKeyProvider.java:90)
at androidx.recyclerview.selection.StableIdKeyProvider$1.onChildViewDetachedFromWindow(StableIdKeyProvider.java:69)
at androidx.recyclerview.widget.RecyclerView.dispatchChildDetached(RecyclerView.java:7546)
at androidx.recyclerview.widget.RecyclerView.removeDetachedView(RecyclerView.java:4349)
at androidx.recyclerview.widget.RecyclerView$LayoutManager.removeAndRecycleScrapInt(RecyclerView.java:9243)
at androidx.recyclerview.widget.RecyclerView.dispatchLayoutStep3(RecyclerView.java:4207)
at androidx.recyclerview.widget.RecyclerView.dispatchLayout(RecyclerView.java:3862)
at androidx.recyclerview.widget.RecyclerView.onLayout(RecyclerView.java:4404)
at android.view.View.layout(View.java:22844)
at android.view.ViewGroup.layout(ViewGroup.java:6389)
at androidx.constraintlayout.widget.ConstraintLayout.onLayout(ConstraintLayout.java:1915)
at android.view.View.layout(View.java:22844)
at android.view.ViewGroup.layout(ViewGroup.java:6389)
at androidx.viewpager.widget.ViewPager.onLayout(ViewPager.java:1775)
at android.view.View.layout(View.java:22844)
at android.view.ViewGroup.layout(ViewGroup.java:6389)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1829)
at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1673)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1582)
at android.view.View.layout(View.java:22844)
at android.view.ViewGroup.layout(ViewGroup.java:6389)
at androidx.coordinatorlayout.widget.CoordinatorLayout.layoutChild(CoordinatorLayout.java:1213)
at androidx.coordinatorlayout.widget.CoordinatorLayout.onLayoutChild(CoordinatorLayout.java:899)
at androidx.coordinatorlayout.widget.CoordinatorLayout.onLayout(CoordinatorLayout.java:919)
at android.view.View.layout(View.java:22844)
at android.view.ViewGroup.layout(ViewGroup.java:6389)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
at android.view.View.layout(View.java:22844)
at android.view.ViewGroup.layout(ViewGroup.java:6389)
at androidx.coordinatorlayout.widget.CoordinatorLayout.layoutChild(CoordinatorLayout.java:1213)
at androidx.coordinatorlayout.widget.CoordinatorLayout.onLayoutChild(CoordinatorLayout.java:899)
at androidx.coordinatorlayout.widget.CoordinatorLayout.onLayout(CoordinatorLayout.java:919)
at android.view.View.layout(View.java:22844)
at android.view.ViewGroup.layout(ViewGroup.java:6389)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1829)
at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1673)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1582)
at android.view.View.layout(View.java:22844)
at android.view.ViewGroup.layout(ViewGroup.java:6389)
at androidx.coordinatorlayout.widget.CoordinatorLayout.layoutChild(CoordinatorLayout.java:1213)
at androidx.coordinatorlayout.widget.CoordinatorLayout.onLayoutChild(CoordinatorLayout.java:899)
at androidx.coordinatorlayout.widget.CoordinatorLayout.onLayout(CoordinatorLayout.java:919)
at android.view.View.layout(View.java:22844)
at android.view.ViewGroup.layout(ViewGroup.java:6389)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
at android.view.View.layout(View.java:22844)
at android.view.ViewGroup.layout(ViewGroup.java:6389)
at androidx.appcompat.widget.ActionBarOverlayLayout.onLayout(ActionBarOverlayLayout.java:446)
at android.view.View.layout(View.java:22844)
at android.view.ViewGroup.layout(ViewGroup.java:6389)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
2020-08-16 16:45:36.416 12939-12939/com.me.myapp E/AndroidRuntime: at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
at android.view.View.layout(View.java:22844)
at android.view.ViewGroup.layout(ViewGroup.java:6389)
at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1829)
at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1673)
at android.widget.LinearLayout.onLayout(LinearLayout.java:1582)
at android.view.View.layout(View.java:22844)
at android.view.ViewGroup.layout(ViewGroup.java:6389)
at android.widget.FrameLayout.layoutChildren(FrameLayout.java:332)
at android.widget.FrameLayout.onLayout(FrameLayout.java:270)
at com.android.internal.policy.DecorView.onLayout(DecorView.java:784)
at android.view.View.layout(View.java:22844)
at android.view.ViewGroup.layout(ViewGroup.java:6389)
at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:3470)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2938)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1952)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:8171)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:972)
at android.view.Choreographer.doCallbacks(Choreographer.java:796)
at android.view.Choreographer.doFrame(Choreographer.java:731)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:957)
at android.os.Handler.handleCallback(Handler.java:938)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:223)
at android.app.ActivityThread.main(ActivityThread.java:7656)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
对话框：
class AddBookDialog : DialogFragment() {
private val TAG = AddBookDialog::class.java.simpleName
private lateinit var listener: AddBookDialogInterface
private lateinit var editTextName: EditText
private lateinit var title: TextView
private var id: String? = null
interface AddBookDialogInterface {
fun addKochbuch(name: String,id: String? = null): Boolean
}
override fun onCreateDialog(savedInstanceState: Bundle?): Dialog {
return activity?.let {
// Use the Builder class for convenient dialog construction
val builder = AlertDialog.Builder(it,R.style.AppTheme_AlertDialog)
val inflater = requireActivity().layoutInflater;
val view = inflater.inflate(R.layout.add_book_dialog,null)
editTextName = view.findViewById(R.id.editTextName)
// editTextNameLayout = view.findViewById(R.id.editTextNameLayout)
title = view.findViewById(R.id.title)
arguments?.let {
it.getString(nameParam).let {
editTextName.setText(it)
}
id = it.getString(idParam)
}
editTextName.setOnKeyListener(View.OnKeyListener { v,keyCode,event ->
if (keyCode == KeyEvent.KEYCODE_ENTER && event.action == KeyEvent.ACTION_UP) {
add()
return@OnKeyListener true
}
false
})
builder.setView(view)
.setPositiveButton(
"Hinzufügen"
) { dialog,id ->
add()
}
.setNegativeButton(
"Abbrechen"
) { dialog,id ->
// User cancelled the dialog
}
// Create the AlertDialog object and return it
val dialog: AlertDialog = builder.create()
dialog.setOnShowListener {
val button: Button = dialog.getButton(AlertDialog.BUTTON_POSITIVE)
button.setOnClickListener {add()}
}
dialog
} ?: throw IllegalStateException("Activity cannot be null")
}
override fun onAttach(context: Context) {
super.onAttach(context)
// Verify that the host activity implements the callback interface
try {
// Instantiate the NoticeDialogListener so we can send events to the host
listener = context as AddBookDialogInterface
} catch (e: ClassCastException) {
// The activity doesn't implement the interface,throw exception
throw ClassCastException((context.toString() +
" must implement AddBookDialogInterface"))
}
}
private fun add() {
val name = editTextName.text.toString()
listener.addKochbuch(name,id).let {
if (it)
dismiss()
}
}
companion object {
fun newInstance(kochbuch: Kochbuch? = null) =
AddBookDialog().apply {
arguments = Bundle().apply {
putString(nameParam,kochbuch?.name)
putString(idParam,kochbuch?.id)
}
}
}
}
对话框布局：
<?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"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<TextView
android:id="@+id/title"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginStart="16dp"
android:layout_marginTop="16dp"
android:layout_marginEnd="16dp"
android:text="Erstelle ein neues Kochbuch"
android:textAppearance="@style/TextAppearance.MaterialComponents.Headline6"
android:textColor="@color/material_on_background_emphasis_high_type"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<com.google.android.material.textfield.TextInputLayout
android:id="@+id/editTextNameLayout"
style="@style/Widget.MaterialComponents.TextInputLayout.OutlinedBox"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginStart="16dp"
android:layout_marginTop="16dp"
android:layout_marginEnd="16dp"
android:layout_marginBottom="16dp"
android:hint="Name deines Kochbuches"
android:textColorHint="@color/input_outline_color"
app:boxStrokeColor="@color/input_outline_color"
app:hintTextColor="@color/input_outline_color"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/title">
<com.google.android.material.textfield.TextInputEditText
android:id="@+id/editTextName"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:singleLine="true"
android:textColor="@color/material_on_background_emphasis_high_type" />
</com.google.android.material.textfield.TextInputLayout>
</androidx.constraintlayout.widget.ConstraintLayout>
片段：
class HomeBooksFragment : Fragment(),OnActionItemClickListener {
private val TAG = HomeBooksFragment::class.java.simpleName
private lateinit var realm: Realm
private val adapter = ItemAdapterCookingBooks()
private lateinit var result: RealmResults<Kochbuch>
private lateinit var tracker: SelectionTracker<Long>
private var actionmode: SelectionActionModeCallback? = null
override fun onCreateView(
inflater: LayoutInflater,container: ViewGroup?,savedInstanceState: Bundle?
): View? {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_home_books,container,false)
}
override fun onActivityCreated(savedInstanceState: Bundle?) {
super.onActivityCreated(savedInstanceState)
realm = Realm.getDefaultInstance()
result = realm.where<Kochbuch>().sort("name").findAll()
result.addChangeListener { t,_ ->
updateUI(t)
}
adapter.data = ArrayList()
rv.layoutManager = GridLayoutManager(context,2)
rv.adapter = adapter
tracker = SelectionTracker.Builder<Long>(
"mySelection",rv,StableIdKeyProvider(rv),ItemDetailLookup(rv),StorageStrategy.createLongStorage()
).withSelectionPredicate(
SelectionPredicates.createSelectAnything()
).build()
tracker.addObserver(
object : SelectionTracker.SelectionObserver<Long>() {
override fun onSelectionChanged() {
super.onSelectionChanged()
tracker.selection.size().let { i ->
when {
i >= 2 -> actionmode?.setEditEnabled(false)
i == 1 -> actionmode?.setEditEnabled(true)
i == 0 -> Log.d(TAG,"onSelectionChanged: zero items selected")
else -> null
}
if (tracker.hasSelection() && actionmode == null) {
actionmode = SelectionActionModeCallback()
view?.let { actionmode?.startActionMode(it,R.menu.selection_action_mode_menu,tracker,"$i Ausgwählt") }
actionmode?.setListener(this@HomeBooksFragment)
} else if (!tracker.hasSelection() && actionmode != null) {
actionmode?.finishActionMode()
actionmode = null
} else {
actionmode?.setTitle("$i Ausgewählt")
}
}
}
}
)
adapter.tracker = tracker
updateUI(result)
}
}
ItemDetailLookup没问题，因为我将所有内容都放入了try-catch块中，并且错误仍然出现。
进一步的调试显示，只有在对话框后面显示和项目时才会发生调试（在我的屏幕上显示7个项目时）。但是，当对话框打开而我的viewpager中显示另一个片段时，也会发生这种情况。由此，我怀疑单击事件是通过对话框以某种方式传递到底层片段的。
任何帮助将不胜感激。
编辑：
在显示其他对话框时也会发生
解决方法
由于某种原因，选择跟踪器试图获取一个不存在或不在recyclerview中且产生了空指针实例的视图持有者的itemdetails。在我的ViewHolder中，我有此方法可返回有关该Viewholder的所有必要信息，以使选择跟踪器正常工作，在这里使用正确的实现是无效的：
fun getItemDetails(): ItemDetailsLookup.ItemDetails<Long> =
object : ItemDetailsLookup.ItemDetails<Long>() {
override fun getPosition(): Int {
try {
return adapterPosition
} catch (e: Exception) {
return -1
}
}
override fun getSelectionKey(): Long? = itemId
}
为比较起见，请问我以前发布的实现的问题。
,可能有点晚了，但是我最近遇到了同样的问题，并找到了对我有用的解决方案。创建一个自定义ItemKeyProvider为我解决了NPE问题。我使用了我在网上找到的这篇文章：A guide to recyclerview selection
class LongItemKeyProvider(private val recyclerView: RecyclerView) :
ItemKeyProvider<Long>(SCOPE_MAPPED) {
override fun getKey(position: Int): Long? {
return recyclerView.adapter?.getItemId(position)
}
override fun getPosition(key: Long): Int {
return recyclerView.findViewHolderForItemId(key)?.layoutPosition ?:
RecyclerView.NO_POSITION
}
}
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