问：

我想制作一个屏幕，您可以在其中根据芯片进行过滤。添加芯片时，出现以下错误：java.lang.NullPointerException: Attempt to invoke virtual method 'boolean androidx.recyclerview.widget.RecyclerView$ViewHolder.shouldIgnore()' on a null object reference

这些是不同的文件：

xml 片段：list_members_fragment.xml

<?xml version="1.0" encoding="utf-8"?>
<layout 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">

    <data>
        <variable
            name="listMembersViewModel"
            type="com.example.test.screens.members.ListMembersViewModel" />
    </data>

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".ListMembersFragment">

        <HorizontalScrollView
            android:id="@+id/chips"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="@dimen/spacing_normal"
            android:contentDescription="@string/horizontal_scrollview"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent">

            <com.google.android.material.chip.ChipGroup
                android:id="@+id/roles_list"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:padding="@dimen/spacing_normal"
                app:singleSelection="true" >
            </com.google.android.material.chip.ChipGroup>
        </HorizontalScrollView>

        <androidx.recyclerview.widget.RecyclerView
            android:id="@+id/member_list"
            android:layout_width="0dp"
            android:layout_height="0dp"
            android:layout_marginStart="@dimen/spacing_small"
            android:layout_marginTop="16dp"
            android:layout_marginEnd="@dimen/spacing_small"
            android:layout_marginBottom="@dimen/spacing_normal"
            app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/chips"/>

    </androidx.constraintlayout.widget.ConstraintLayout>

</layout>

用于存储一个芯片的 xml 布局文件roles.xml

<?xml version="1.0" encoding="utf-8"?>
<com.google.android.material.chip.Chip xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    style="@style/Widget.MaterialComponents.Chip.Choice">

</com.google.android.material.chip.Chip>

ListMembersFragment.kt

这是发生错误的地方，行chipGroup.addView（chip）使应用程序崩溃

class ListMembersFragment : Fragment() {
    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View {

        val binding: ListMembersFragmentBinding =
            DataBindingUtil.inflate(inflater, R.layout.list_members_fragment, container, false)

        val viewModelFactory = ListMembersViewModelFactory()
        val viewModel = ViewModelProvider(this, viewModelFactory)[ListMembersViewModel::class.java]

        binding.listMembersViewModel = viewModel
        binding.lifecycleOwner = this

        val adapter = ListMembersAdapter( MemberListener{
                memberID ->
            findNavController().navigate(
                ListMembersFragmentDirections.actionListMembersFragmentToMemberFragment(
                memberID
            ))
        })
        val recyclerView = binding.memberList
        recyclerView.adapter = adapter

        viewModel.listMembers.observe(viewLifecycleOwner) { adapter.submitList(it) }

        viewModel.listMembers.observe(viewLifecycleOwner, object: Observer<List<Member>> {
            override fun onChanged(data: List<Member>?) {
                data ?: return

                //1: Make a new Chip view for each item in the list
                try {
                    val chipGroup = binding.memberList
                    val inflator =  LayoutInflater.from(chipGroup.context)

                    var children = data.map { member ->
                        val role = member.role
                        val chip = inflator.inflate(R.layout.roles, chipGroup, false) as Chip
                        chip.text = role.toString()
                        chip.tag = role.toString()
                        chip.setOnCheckedChangeListener{ button, isChecked ->
                            viewModel.onFilterChanged(button.tag as String, isChecked)
                        }
                        chip
                    }.distinctBy { it.tag }

                    //2: Remove any views already in the ChipGroup
                    chipGroup.removeAllViews()

                    //3: Add the new children to the ChipGroup
                    for (chip in children) {
                        Log.i("ListMembersFragment", chip.tag.toString())
                        chipGroup.addView(chip)
                    }

                    Log.i("ListMembersFragment", "ADDED CHILDREN TO CHIPGROUP VIEW")
                } catch (er: Error) {
                    Log.e("ListMembersFragment", er.toString())
                }

            }
        })

        return binding.root
    }
}

ListMembersViewModel.kt

class ListMembersViewModel : ViewModel() {

    private var _filter = FilterHolder()

    private val _listMembers = MutableLiveData<List<Member>>()
    val listMembers: LiveData<List<Member>>
        get() = _listMembers

    init {
        initializeLiveData()
    }

    private fun initializeLiveData(){
        viewModelScope.launch {
            _listMembers.value = MemberMock().members
        }
    }

    fun onFilterChanged(filter: String, isChecked: Boolean) {
        Log.i("ListMembersViewModel", "In method onFilterChanged")
        if (this._filter.update(filter, isChecked)) {

            val members = MemberMock().members
            _listMembers.value = members.filter { m ->
                m.role.toString() == _filter.currentValue
            }
        } else {
            _listMembers.value = MemberMock().members
        }
    }

    private class FilterHolder {
        var currentValue: String? = null
            private set

        fun update(changedFilter: String, isChecked: Boolean): Boolean {
            Log.i("ListMembersViewModel", "In class method update in FilterHolder")
            if (isChecked) {
                currentValue = changedFilter
                return true
            } else if (currentValue == changedFilter) {
                currentValue = null
                return true
            }
            return false
        }
    }
}

我真的不知道问题发生在哪里。以下是完整的例外情况：

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.test, PID: 31991
    java.lang.NullPointerException: Attempt to invoke virtual method 'boolean androidx.recyclerview.widget.RecyclerView$ViewHolder.shouldIgnore()' on a null object reference
        at androidx.recyclerview.widget.RecyclerView.findMinMaxChildLayoutPositions(RecyclerView.java:4485)
        at androidx.recyclerview.widget.RecyclerView.dispatchLayoutStep1(RecyclerView.java:4215)
        at androidx.recyclerview.widget.RecyclerView.dispatchLayout(RecyclerView.java:4010)
        at androidx.recyclerview.widget.RecyclerView.onLayout(RecyclerView.java:4578)
        at android.view.View.layout(View.java:20672)
        at android.view.ViewGroup.layout(ViewGroup.java:6194)
        at androidx.constraintlayout.widget.ConstraintLayout.onLayout(ConstraintLayout.java:1873)
        at android.view.View.layout(View.java:20672)
        at android.view.ViewGroup.layout(ViewGroup.java:6194)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
        at android.view.View.layout(View.java:20672)
        at android.view.ViewGroup.layout(ViewGroup.java:6194)
        at androidx.constraintlayout.widget.ConstraintLayout.onLayout(ConstraintLayout.java:1873)
        at android.view.View.layout(View.java:20672)
        at android.view.ViewGroup.layout(ViewGroup.java:6194)
        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:20672)
        at android.view.ViewGroup.layout(ViewGroup.java:6194)
        at androidx.drawerlayout.widget.DrawerLayout.onLayout(DrawerLayout.java:1263)
        at android.view.View.layout(View.java:20672)
        at android.view.ViewGroup.layout(ViewGroup.java:6194)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
        at android.view.View.layout(View.java:20672)
        at android.view.ViewGroup.layout(ViewGroup.java:6194)
        at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1812)
        at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1656)
        at android.widget.LinearLayout.onLayout(LinearLayout.java:1565)
        at android.view.View.layout(View.java:20672)
        at android.view.ViewGroup.layout(ViewGroup.java:6194)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
        at android.view.View.layout(View.java:20672)
        at android.view.ViewGroup.layout(ViewGroup.java:6194)
        at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1812)
        at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1656)
        at android.widget.LinearLayout.onLayout(LinearLayout.java:1565)
        at android.view.View.layout(View.java:20672)
        at android.view.ViewGroup.layout(ViewGroup.java:6194)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
        at com.android.internal.policy.DecorView.onLayout(DecorView.java:753)
        at android.view.View.layout(View.java:20672)
        at android.view.ViewGroup.layout(ViewGroup.java:6194)
        at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:2792)
        at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2319)
        at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1460)
        at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:7183)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:949)
        at android.view.Choreographer.doCallbacks(Choreographer.java:761)
        at android.view.Choreographer.doFrame(Choreographer.java:696)
        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:935)
        at android.os.Handler.handleCallback(Handler.java:873)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:193)
E/AndroidRuntime:     at android.app.ActivityThread.main(ActivityThread.java:6669)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)