Question

这是我的项目聊天应用程序。问题是，当我在android上运行该应用程序时，尝试从Firebase数据库检索聊天。

错误：

E / Android运行时：致命异常：主要流程：com.example.chatapp，PID：24371 java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法'boolean java.lang.String.equals（java.lang.Object）' 在com.example.chatapp.Message_chat $ 4.onDataChange（Message_chat.java:150）

Message_chat.java:150

 if (chat.getReceiver().equals(myid) && chat.getSender().equals(userid) ||
                        chat.getReceiver().equals(userid) && chat.getSender().equals(myid)) {
                    mList.add(chat);
                }

源代码错误

如果（chat.getReceiver（）。equals（myid）&& chat.getSender（）。equals（userid）|| chat.getReceiver（）。equals（userid）&& chat.getSender（）。equals（myid））{ mList.add（聊天）; }

错误

private void readMessage (final String myid, final String userid, final String imageurl){
mList = new ArrayList<>();

databaseReference = FirebaseDatabase.getInstance().getReference("Chats");
databaseReference.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
        mList.clear();
        for (DataSnapshot snapshot : dataSnapshot.getChildren()){
            Chat chat = snapshot.getValue(Chat.class);
            if (chat.getReceiver().equals(myid) && chat.getSender().equals(userid) ||
                    chat.getReceiver().equals(userid) && chat.getSender().equals(myid)) {
                mList.add(chat);
            }
            messageAdapter = new MessageAdapter(Message_chat.this, mList, imageurl);
            recyclerView.setAdapter(messageAdapter);
        }
    }

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

    }
});

列表项

public class Chat {

private String sender, receiver, message;

public Chat(String sender, String receiver, String message) {
    this.sender = sender;
    this.receiver = receiver;
    this.message = message;
}

public Chat() {
}

public String getSender() {
    return sender;
}

public void setSender(String sender) {
    this.sender = sender;
}

public String getReceiver() {
    return receiver;
}

public void setReceiver(String receiver) {
    this.receiver = receiver;
}

public String getMessage() {
    return message;
}

public void setMessage(String message) {
    this.message = message;
 }
}

适配器

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

private static final int MSG_TYPE_LEFT = 0;
public static final int MSG_TYPE_RIGHT = 1;

private Context context;
private List<Chat> chatList;
private String imagerurl;

private FirebaseUser firebaseUser;

public MessageAdapter(Context context, List<Chat> chatList, String imagerurl){
    this.context = context;
    this.chatList = chatList;
    this.imagerurl = imagerurl;
}

@NonNull
@Override
public MessageAdapter.ViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {
    if (i == MSG_TYPE_RIGHT) {
        View view = LayoutInflater.from(context).inflate(R.layout.chatmsg_right, viewGroup, false);
        return new MessageAdapter.ViewHolder(view);
    } else {
        View view = LayoutInflater.from(context).inflate(R.layout.chatmsg_left, viewGroup, false);
        return new MessageAdapter.ViewHolder(view);
    }
}

@Override
public void onBindViewHolder(@NonNull MessageAdapter.ViewHolder viewHolder, int i) {

    Chat chat = chatList.get(i);

    viewHolder.show_message.setText(chat.getMessage());

    if (imagerurl.equals("default")){
        viewHolder.profile_image.setImageResource(R.mipmap.ic_launcher);
    } else {
        Glide.with(context).load(imagerurl).into(viewHolder.profile_image);
    }

}

@Override
public int getItemCount() {

    return chatList.size();
}

public class ViewHolder extends RecyclerView.ViewHolder{

    public TextView show_message;
    public ImageView profile_image;

    public ViewHolder(View itemView){
        super(itemView);

        show_message = itemView.findViewById(R.id.show_messageR);
        profile_image = itemView.findViewById(R.id.profile_imageR);
    }
}

@Override
public int getItemViewType(int position) {
    firebaseUser = FirebaseAuth.getInstance().getCurrentUser();
    if (chatList.get(position).getSender().equals(firebaseUser.getUid())){
        return MSG_TYPE_RIGHT;
    }else {
        return MSG_TYPE_LEFT;
    }
}
}

这是消息聊天（聊天活动）中的全部代码

通过导入使用de.hdodenhof.circleimageview.CircleImageView的“圆形图像视图”；

public class Message_chat extends AppCompatActivity {

CircleImageView profileimage;
TextView username;

FirebaseUser firebaseUser;
DatabaseReference databaseReference;

ImageButton btnsendMessage;
EditText messageBox;

MessageAdapter messageAdapter;
List<Chat> mList;

RecyclerView recyclerView;

Intent intentMsgChat;

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

    Toolbar toolbar = findViewById(R.id.toolbarMsgChat);
    setSupportActionBar(toolbar);
    Objects.requireNonNull(getSupportActionBar()).setTitle("");
    getSupportActionBar().setDisplayHomeAsUpEnabled(true);
    toolbar.setNavigationOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            finish();
        }
    });

    recyclerView = findViewById(R.id.recyclerviewMsgChat);
    recyclerView.setHasFixedSize(true);

    LinearLayoutManager linearLayoutManager = new LinearLayoutManager(getApplicationContext());
    linearLayoutManager.setStackFromEnd(true);
    recyclerView.setLayoutManager(linearLayoutManager);

    profileimage = findViewById(R.id.imageprofileMsgChat);
    username = findViewById(R.id.usernameMsgChat);
    btnsendMessage = findViewById(R.id.btnsendMsgChat);
    messageBox = findViewById(R.id.boxmessageMsgChat);

    intentMsgChat = getIntent();
    final String userid = intentMsgChat.getStringExtra("UserID");

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

    btnsendMessage.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            String msg = messageBox.getText().toString();
            if (!msg.equals("")) {
                setSendMessage(firebaseUser.getUid(), userid, msg);
            } else {
                Toast.makeText(Message_chat.this, "Message is empty", Toast.LENGTH_SHORT).show();
            }

            messageBox.setText("");
        }
    });

    databaseReference = FirebaseDatabase.getInstance().getReference("Users").child(userid);

    databaseReference.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            Userprofile userprofile = dataSnapshot.getValue(Userprofile.class);

            assert userprofile != null;
            username.setText(userprofile.getUsername());

            if (userprofile.getImageURL().equals("default")) {
                profileimage.setImageResource(R.mipmap.ic_launcher);
            } else {
                Glide.with(Message_chat.this).load(userprofile.getImageURL()).into(profileimage);
            }

            readMessage(firebaseUser.getUid(), userid, userprofile.getImageURL());
        }

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

        }
    });
}


    private void setSendMessage (String sender, String receiver, String message){

        DatabaseReference reference = FirebaseDatabase.getInstance().getReference();

        HashMap<String, Object> hashMap = new HashMap<>();

        hashMap.put("Sender", sender);
        hashMap.put("Receiver", receiver);
        hashMap.put("Message", message);

        reference.child("Chats").push().setValue(hashMap);
    }

private void readMessage (final String myid, final String userid, final String imageurl){
    mList = new ArrayList<>();

    databaseReference = FirebaseDatabase.getInstance().getReference("Chats");
    databaseReference.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            mList.clear();
            for (DataSnapshot snapshot : dataSnapshot.getChildren()){
                Chat chat = snapshot.getValue(Chat.class);
                if (chat.getReceiver().equals(myid) && chat.getSender().equals(userid) ||
                        chat.getReceiver().equals(userid) && chat.getSender().equals(myid)) {
                    mList.add(chat);
                }
                messageAdapter = new MessageAdapter(Message_chat.this, mList, imageurl);
                recyclerView.setAdapter(messageAdapter);
            }
        }

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

        }
    });
}
}

聊天中的错误代码聊天= snapshot.getValue（Chat.class）

0 个答案: