我的应用程序工作得很好，当我刚刚有片段的xml中的recyclerview，但我需要 Package 它在constraintlayout的一些原因，但我的应用程序开始崩溃后。

错误消息：

*java.lang.IllegalStateException: The specified child already has a parent. You must call removeView() on the child's parent first.*

片段代码

public class AdminPostFragment extends Fragment  {

        RecyclerView recyclerView;
        DatabaseReference database;
        MyAdapter myAdapter;
        ArrayList<Updates> list;
        private FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser();

        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                                 Bundle savedInstanceState) {
            // Inflate the layout for this fragment
            View view = inflater.inflate(R.layout.fragment_admin_post, container, false);
            recyclerView = view.findViewById(R.id.updates_recycler);
            recyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));

             if (FirebaseAuth.getInstance().getCurrentUser() != null) {
            FirebaseRecyclerOptions<Updates> options =
                    new FirebaseRecyclerOptions.Builder<Updates>()
                            .setQuery(FirebaseDatabase.getInstance().getReference().child("updates"), Updates.class)
                            .build();

            myAdapter = new MyAdapter(options);

            recyclerView.setAdapter(myAdapter);
            myAdapter.notifyDataSetChanged();
        }
        ItemTouchHelper itemTouchHelper = new ItemTouchHelper(simpleCallback);
        itemTouchHelper.attachToRecyclerView(recyclerView);

            return recyclerView;
        }

片段XML文件

<?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_height="match_parent"
        android:layout_width="match_parent"
        android:id="@+id/parent">

        <androidx.recyclerview.widget.RecyclerView

            android:id="@+id/updates_recycler"
            android:layout_width="match_parent"

            android:layout_height="match_parent"
            android:scrollbars="vertical"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.0"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintVertical_bias="1.0">

        </androidx.recyclerview.widget.RecyclerView>

    </androidx.constraintlayout.widget.ConstraintLayout>

我的适配器代码

package com.project.adminapp.adapter;



import java.util.ArrayList;
.....

public class MyAdapter extends FirebaseRecyclerAdapter< Updates ,MyAdapter.MyViewHolder> {

    public MyAdapter(@NonNull FirebaseRecyclerOptions<Updates> options)
    {
        super(options);
    }

    @Override
    protected void onBindViewHolder(@NonNull  final MyViewHolder holder,  final int position, @NonNull  final Updates model) {
        holder.updates_text.setText(model.getUpdate());



    }

    @NonNull
    @Override
    public MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.updates,parent,false);
        return new MyViewHolder(v);
    }


    public  class MyViewHolder extends RecyclerView.ViewHolder
    {
        TextView  updates_text ;
        public MyViewHolder(@NonNull View itemView) {
            super(itemView);

            updates_text = (TextView) itemView.findViewById(R.id.updates_text);

        }
    }

}

当我使用如下代码时：

recyclerview = 
(RecyclerView) inflater.inflate(R.layout.fragment_admin_post, container, false);

得到类转换异常ConstraintLayout cannot be cast to recyclerview.