从 Adapter 调用一个方法到 Fragment 并用它传递一个变量 Android Studio

问题描述

所以我想要的是从我的回收器视图中单击一个按钮，应该调用我片段中的方法/函数，同时它也应该发送一个变量。我知道我可以使用侦听器或接口，但我已经查看并实施了几个解决方案，但没有一个通常可以正常工作 空指针异常 我不知道我在做什么，所以如果有人让我知道如何做，这会很有帮助通过查看我的代码，我也从我的适配器中删除了一些不必要的部分..

适配器

public class AddPartAdapter extends RecyclerView.Adapter<AddPartAdapter.ViewHolder> {

private  Context mContext;
private  List<User> mUsers;

EventListener listener;



public interface EventListener {
    void AddParticipant(String id);
}

public void addEventListener(EventListener listener){
    this.listener = listener;
}

public void removeEventListener(){
    listener = null;
}


public AddPartAdapter(Context mContext,List<User> mUsers) {
    this.mContext = mContext;
    this.mUsers = mUsers;

}



@NonNull
@Override
public AddPartAdapter.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent,int viewType) {
    ViewGroup viewGroup = (ViewGroup) LayoutInflater.from(mContext).inflate(R.layout.add_part_item,parent,false);
    return new AddPartAdapter.ViewHolder(viewGroup);
}

@Override
public void onBindViewHolder(@NonNull AddPartAdapter.ViewHolder holder,int position) {
    final User user = mUsers.get(position);

    holder.username.setText(user.getUsername());
    holder.dt.setText(user.getDt());

    if (user.getimageUrl().equals("default")) {
        holder.dp.setimageResource(R.drawable.user);
    } else {
        Glide.with(mContext).load(user.getimageUrl()).into(holder.dp);
    }

    holder.addpart_btn.setonClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            String Variable = user.getId();//This is the variable that should pass
            //Send call that method and send the variablethat variable to Fragment
            listener.AddParticipant(Variable);
        }
    });

}

碎片

public class AddParticipantsFragment extends Fragment implements AddPartAdapter.EventListener {

private RecyclerView recyclerView;
private List<User> mUsers;

DatabaseReference databaseReference;
FirebaseUser firebaseUser;

private List<Chatlist>usersList;

private AddPartAdapter addPartAdapter;

public String groupId;



@Override
public View onCreateView(LayoutInflater inflater,ViewGroup container,Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    View view = inflater.inflate(R.layout.fragment_add_participants,container,false);
    recyclerView = view.findViewById(R.id.recycler_view);
    recyclerView.setHasFixedSize(true);
    recyclerView.setLayoutManager(new linearlayoutmanager(getContext()));
    usersList = new ArrayList<>();
    firebaseUser = FirebaseAuth.getInstance().getCurrentUser();
    databaseReference = FirebaseDatabase.getInstance().getReference("Chatlist").child(firebaseUser.getUid());
    databaseReference.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot snapshot) {
            usersList.clear();
            for(DataSnapshot snapshot1 : snapshot.getChildren()){
                Chatlist chatlist = snapshot1.getValue(Chatlist.class);
                usersList.add(chatlist);
            }



            chatList();
        }

        @Override
        public void onCancelled(@NonNull DatabaseError error) {

        }
    });

    AddParticipants activity = (AddParticipants) getActivity();
    assert activity != null;
    groupId = activity.getMyData();
    return view;
}



private void chatList() {

    mUsers = new ArrayList<>();
    databaseReference = FirebaseDatabase.getInstance().getReference("Users");
    databaseReference.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot snapshot) {
            mUsers.clear();
            for (DataSnapshot snapshot1 : snapshot.getChildren()){
                User user = snapshot1.getValue(User.class);
                for (Chatlist chatlist : usersList){
                    assert user != null;
                    if(user.getId().equals(chatlist.getId())){
                        if(chatlist.getFriends().equals("Messaged")){
                            mUsers.add(user);

                        }if (chatlist.getFriends().equals("Requested")){
                            //Donothing
                        }
                        if(chatlist.getFriends().equals("Blocked")){
                            //Dont do anything
                        }

                    }


                }

            }



            AddPartAdapter addPartAdapter = new AddPartAdapter(getContext(),mUsers);
            addPartAdapter.addEventListener();//Here inside the bracket what to add.
            recyclerView.setAdapter(addPartAdapter);
        }

        @Override
        public void onCancelled(@NonNull DatabaseError error) {

        }
    });
}




public void AddParticipant(String id) {
    //And it should initialize this method
    DatabaseReference databaseReference = FirebaseDatabase.getInstance().getReference("Grouplist").child(groupId);
    HashMap<String,String> hashMap1 = new HashMap<>();
    hashMap1.put("id",id);
    hashMap1.put("admin","false");
    databaseReference.setValue(hashMap1);
}

public void onDestroy() {
    super.onDestroy();
    addPartAdapter.removeEventListener();
}
}

这里是 logcat

java.lang.NullPointerException：尝试在空对象引用上调用接口方法“void com.margsapp.messenger.Adapter.AddPartAdapter$EventListener.AddParticipant(java.lang.String)” 在 com.margsapp.messenger.Adapter.AddPartAdapter$1.onClick(AddPartAdapter.java:70) 在 android.view.View.performClick(View.java:7125) 在 android.view.View.performClickInternal(View.java:7102) 在 android.view.View.access$3500(View.java:801) 在 android.view.View$PerformClick.run(View.java:27336) 在 android.os.Handler.handleCallback(Handler.java:883) 在 android.os.Handler.dispatchMessage(Handler.java:100) 在 android.os.Looper.loop(Looper.java:214) 在 android.app.ActivityThread.main(ActivityThread.java:7356) 在 java.lang.reflect.Method.invoke(Native Method) 在 com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492) 在 com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)

解决方法

试试这个方法，

在您的适配器类中，创建 2 个方法。添加和删​​除侦听器。

public addEventListener(EventListener listener){
    this.listener = listener;
}

public removeEventListener(){
   listener = null;
}

片段类

public class AddParticipantsFragment extends Fragment implements AddPartAdapter.EventListener  {

private RecyclerView recyclerView;
private List<User> mUsers;

DatabaseReference databaseReference;
FirebaseUser firebaseUser;

private List<Chatlist>usersList;


public String groupId;
private AddPartAdapter addPartAdapter



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

    usersList = new ArrayList<>();

    firebaseUser = FirebaseAuth.getInstance().getCurrentUser();

    databaseReference = FirebaseDatabase.getInstance().getReference("Chatlist").child(firebaseUser.getUid());
    databaseReference.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot snapshot) {
            usersList.clear();
            for(DataSnapshot snapshot1 : snapshot.getChildren()){
                Chatlist chatlist = snapshot1.getValue(Chatlist.class);
                usersList.add(chatlist);
            }

            chatList();
        }

        @Override
        public void onCancelled(@NonNull DatabaseError error) {

        }
    });

    AddParticipants activity = (AddParticipants) getActivity();
    assert activity != null;
    groupId = activity.getMyData();


    return view;
}



private void chatList() {

    mUsers = new ArrayList<>();
    databaseReference = FirebaseDatabase.getInstance().getReference("Users");
    databaseReference.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot snapshot) {
            mUsers.clear();
            for (DataSnapshot snapshot1 : snapshot.getChildren()){
                User user = snapshot1.getValue(User.class);
                for (Chatlist chatlist : usersList){
                    assert user != null;
                    if(user.getId().equals(chatlist.getId())){
                        if(chatlist.getFriends().equals("Messaged")){
                            mUsers.add(user);

                        }if (chatlist.getFriends().equals("Requested")){
                            //DoNothing
                        }
                        if(chatlist.getFriends().equals("Blocked")){
                            //Dont do anything
                        }

                    }


                }

            }



            addPartAdapter = new AddPartAdapter(getContext(),mUsers);
            adapter.addEventListener(this)
            recyclerView.setAdapter(addPartAdapter);
        }

        @Override
        public void onCancelled(@NonNull DatabaseError error) {

        }
    });
}



 //This is the method that should be called and id is the variable I want
 public void AddParticipant(String id) {
    //And it should initialize this method
    DatabaseReference databaseReference = FirebaseDatabase.getInstance().getReference("Grouplist").child(groupId);
    HashMap<String,String> hashMap1 = new HashMap<>();
    hashMap1.put("id",id);
    hashMap1.put("admin","false");
    databaseReference.setValue(hashMap1);
 }


 override fun onDestroy() {
        super.onDestroy()
        adapter.removeEventListener()
    }

}