Android can'；t从另一个片段将项目添加到我的回收器视图

我有一个有五个片段的活动，其中一个片段是通知片段，它有一个回收器视图，在该视图中，在收到通知时应该填充通知。现在我有了一个函数，可以将项目添加到recycler视图，但是当我尝试从另一个片段添加它时，它会抛出null引用错误

这是一个片段，其中有回收器和在recyclerview上添加项目的功能

@Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        final View v = inflater.inflate (R.layout.fragment_notificationcict, container, false);



        notimodels = new ArrayList<> ();
        RecyclerView mRecyclerView = v.findViewById (R.id.notificationsRecycler);
        mRecyclerView.setHasFixedSize (true);
        mLayoutManager = new LinearLayoutManager (getContext ());
        mAdapter = new NotificationAdapter (notimodels);
        mRecyclerView.setLayoutManager (mLayoutManager);
        mRecyclerView.setAdapter (mAdapter);
}
 public void addItem(NotificationModel n)
    {
        notimodels = new ArrayList<> ();
        notimodels.add (n);
        mAdapter.notifyItemInserted (notimodels.size () -1);
    }

这是错误信息

rocess: com.univibezstudios.ocappservice.ocapp, PID: 27625
    java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.recyclerview.widget.RecyclerView$Adapter.notifyItemInserted(int)' on a null object reference
        at com.univibezstudios.ocappservice.ocapp.Fragments.NotificationFragmentCict.addItem(NotificationFragmentCict.java:99)
        at com.univibezstudios.ocappservice.ocapp.Fragments.AccountFragmentCict$4$1$1.onDataChange(AccountFragmentCict.java:374)
        at com.google.firebase.database.core.ValueEventRegistration.fireEvent(com.google.firebase:firebase-database@@19.2.1:75)
        at com.google.firebase.database.core.view.DataEvent.fire(com.google.firebase:firebase-database@@19.2.1:63)
        at com.google.firebase.database.core.view.EventRaiser$1.run(com.google.firebase:firebase-database@@19.2.1:55)
        at android.os.Handler.handleCallback(Handler.java:873)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:193)
        at android.app.ActivityThread.main(ActivityThread.java:6803)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:497)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)

---

看，这是片段A

package com.codinginflow.fragmentcommunicationexample;

import android.content.Context;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;


public class FragmentA extends Fragment {
    private FragmentAListener listener;
    private EditText editText;
    private Button buttonOk;

    public interface FragmentAListener {
        void addItemsToFragmentB();
    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.fragment_a, container, false);

        editText = v.findViewById(R.id.edit_text);
        buttonOk = v.findViewById(R.id.button_ok);
        buttonOk.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                addItemsToFragmentB();
        });

        return v;
    }

    public void updateEditText(CharSequence newText) {
        editText.setText(newText);
    }

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        if (context instanceof FragmentAListener) {
            listener = (FragmentAListener) context;
        } else {
            throw new RuntimeException(context.toString()
                    + " must implement FragmentAListener");
        }
    }

    @Override
    public void onDetach() {
        super.onDetach();
        listener = null;
    }
}

这是片段B

package com.codinginflow.fragmentcommunicationexample;

import android.content.Context;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;


public class FragmentB extends Fragment {
    private FragmentBListener listener;
    private EditText editText;
    private Button buttonOk;

    public interface FragmentBListener {
         addItemsToFragmentA();
    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View v = inflater.inflate(R.layout.fragment_b, container, false);

        editText = v.findViewById(R.id.edit_text);
        buttonOk = v.findViewById(R.id.button_ok);
        buttonOk.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                addItemsToFragmentA();
            }
        });

        return v;
    }

    public void updateEditText(CharSequence newText) {
        editText.setText(newText);
    }

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        if (context instanceof FragmentBListener) {
            listener = (FragmentBListener) context;
        } else {
            throw new RuntimeException(context.toString()
                    + " must implement FragmentBListener");
        }
    }

    @Override
    public void onDetach() {
        super.onDetach();
        listener = null;
    }
}

这是一项活动，您将在其中向“回收者”视图中添加项目

package com.codinginflow.fragmentcommunicationexample;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

public class MainActivity extends AppCompatActivity implements FragmentA.FragmentAListener, FragmentB.FragmentBListener {
    private FragmentA fragmentA;
    private FragmentB fragmentB;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        fragmentA = new FragmentA();
        fragmentB = new FragmentB();

        getSupportFragmentManager().beginTransaction()
                .replace(R.id.container_a, fragmentA)
                .replace(R.id.container_b, fragmentB)
                .commit();
    }

    @Override
    public void addItemsToFragmentA() {
          fragmentB.updateEditText(input);
    }

    @Override
    public void addItemsToFragmentB() {
        fragmentA.updateEditText(input);
    }
}

---

你应该和一个片段和另一个片段通信，如下面的链接。。。使用界面谢谢，但您建议的教程只是用于发送数据，但我的问题是从不同的片段访问recycler视图，并能够从那里添加项目@arunabimanyun，而不是在添加项目时创建该片段的新实例…全局保留该片段的引用…并调用addItem方法从这个角度来看，请告诉我我是一个android开发的新手，尤其是fragments@ArunAbimanyuso是什么方法，我应该在我的通知fragments界面上传递什么方法通过addItemsToFragmentB（NotificationModel NotificationModel）这样的界面传递你的值嘿，兄弟，传递什么现在让我很困惑，你能告诉我如何使用公共接口NotificationListener{void AddItems（ArrayList notificationModels）；}

package com.codinginflow.fragmentcommunicationexample;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

public class MainActivity extends AppCompatActivity implements FragmentA.FragmentAListener, FragmentB.FragmentBListener {
    private FragmentA fragmentA;
    private FragmentB fragmentB;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        fragmentA = new FragmentA();
        fragmentB = new FragmentB();

        getSupportFragmentManager().beginTransaction()
                .replace(R.id.container_a, fragmentA)
                .replace(R.id.container_b, fragmentB)
                .commit();
    }

    @Override
    public void addItemsToFragmentA() {
          fragmentB.updateEditText(input);
    }

    @Override
    public void addItemsToFragmentB() {
        fragmentA.updateEditText(input);
    }
}