android - Firebase onDataChange 避免 if 语句

Question

下面的代码适用于我的 firebase 项目，当我在我的方法中注释if 语句时，应用程序不会发生冲突，但无法在 recyclerView 中显示消息。我正在构建聊天应用程序onDatachangeUserChatActivity.java

Logcat 错误信息

[`2020-01-17 16:18:28.327 28690-28690/com.runyankole.runyankole.runyankole E/RecyclerView: No adapter attached; skipping layout
2020-01-17 16:18:28.328 28690-28690/com.runyankole.runyankole.runyankole E/RecyclerView: No adapter attached; skipping layout
2020-01-17 16:18:36.104 28690-28690/? E/RecyclerView: No adapter attached; skipping layout
2020-01-17 16:18:36.111 28690-28690/? E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.runyankole.runyankole.runyankole, PID: 28690
    java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.equals(java.lang.Object)' on a null object reference
        at com.runyankole.runyankole.runyankole.UserChatActivity$4.onDataChange(UserChatActivity.java:151)
        at com.google.firebase.database.core.ValueEventRegistration.fireEvent(com.google.firebase:firebase-database@@19.2.0:75)
        at com.google.firebase.database.core.view.DataEvent.fire(com.google.firebase:firebase-database@@19.2.0:63)
        at com.google.firebase.database.core.view.EventRaiser$1.run(com.google.firebase:firebase-database@@19.2.0:55)
        at android.os.Handler.handleCallback(Handler.java:836)
        at android.os.Handler.dispatchMessage(Handler.java:103)
        at android.os.Looper.loop(Looper.java:203)
        at android.app.ActivityThread.main(ActivityThread.java:6292)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1094)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:955)`][1]

UserChatActivity.java

package com.runyankole.runyankole.runyankole;

import android.content.Intent;
import android.os.Build;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.ImageButton;
import android.widget.TextView;
import android.widget.Toast;

import com.bumptech.glide.Glide;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.ValueEventListener;
import com.google.firebase.database.core.Tag;
import com.rengwuxian.materialedittext.MaterialEditText;
import com.runyankole.runyankole.runyankole.Adapter.MessageAdapter;
import com.runyankole.runyankole.runyankole.Model.Chat;
import com.runyankole.runyankole.runyankole.Model.User;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Objects;

import androidx.annotation.NonNull;
import androidx.annotation.RequiresApi;
import androidx.appcompat.app.AppCompatActivity;
import androidx.appcompat.widget.Toolbar;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import de.hdodenhof.circleimageview.CircleImageView;

public class UserChatActivity extends AppCompatActivity {
    CircleImageView profile_image;
    TextView username;

    FirebaseUser firebaseUser;
    private DatabaseReference reference;

    ImageButton sendBtn;
    MaterialEditText txt_send;

    MessageAdapter messageAdapter;
    List<Chat> mchat;

    RecyclerView recyclerView;

    Intent intent;

    @RequiresApi(api = Build.VERSION_CODES.KITKAT)
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_user_chat);

        Toolbar toolbar = findViewById(R.id.toolbar);
        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.recycler_view);
        recyclerView.setHasFixedSize(true);
        LinearLayoutManager linearLayoutManager = new LinearLayoutManager(getApplicationContext());
        linearLayoutManager.setStackFromEnd(true);
        recyclerView.setLayoutManager(linearLayoutManager);


        profile_image = findViewById(R.id.profile_image);
        username = findViewById(R.id.username);
        sendBtn = findViewById(R.id.btn_send);
        txt_send = findViewById(R.id.sendMessage);

        intent = getIntent();
        final String userid = intent.getStringExtra("userid");
        firebaseUser = FirebaseAuth.getInstance().getCurrentUser();


        sendBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String msg = Objects.requireNonNull(txt_send.getText()).toString();
                if (!msg.equals("")) {
                    sendMessages(firebaseUser.getUid(), userid, msg);
                }else {
                    Toast.makeText(getApplicationContext(),"",Toast.LENGTH_LONG).show();
                }
                txt_send.setText("");
            }
        });


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

        reference.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                User user = dataSnapshot.getValue(User.class);
                assert user != null;
                username.setText(user.getUsername());
                if (user.getImageURL().equals("default")) {
                    profile_image.setImageResource(R.drawable.profile);
                } else {
                    Glide.with(UserChatActivity.this).load(user.getImageURL()).into(profile_image);
                }
                readMessages(firebaseUser.getUid(), userid, user.getImageURL());
            }

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

            }
        });
    }

    private void sendMessages(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 readMessages(final String myid, final String userid, final String imageurl) {
        mchat = new ArrayList<>();
        reference = FirebaseDatabase.getInstance().getReference("Chats");
        reference.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
               mchat.clear();

                for (DataSnapshot snapshot : dataSnapshot.getChildren()) {

                    Chat chat = snapshot.getValue(Chat.class);

                    assert chat != null;
                   // private boolean isQueryingFinished = false;
                    if (chat.getReceiver().equals(myid) && chat.getSender().equals(userid)||
                         chat.getReceiver().equals(userid) && chat.getSender().equals(myid)) {
                          mchat.add(chat);
                }

                }

                messageAdapter = new MessageAdapter(UserChatActivity.this, mchat,imageurl);
                recyclerView.setAdapter(messageAdapter);
            }

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

            }
        });
    }
}

消息适配器.java

package com.runyankole.runyankole.runyankole.Adapter;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;

import com.bumptech.glide.Glide;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
import com.runyankole.runyankole.runyankole.Model.Chat;
import com.runyankole.runyankole.runyankole.R;

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

import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;
import de.hdodenhof.circleimageview.CircleImageView;

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

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

    private Context mContext;
    private List<Chat> mChat;
    private String imageurl;

    FirebaseUser firebaseUser;

    public MessageAdapter(Context mContext, List<Chat> mChat, String imageurl) {
        this.mContext = mContext;
        this.mChat = mChat;
        this.imageurl = imageurl;
    }

    @NonNull
    @Override
    public MessageAdapter.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        if(viewType == MSG_TYPE_RIGHT) {
            View view = LayoutInflater.from(mContext).inflate(R.layout.chat_item_right, parent, false);
           //  view.findViewById(R.id.recycler_view);
            return new MessageAdapter.ViewHolder(view);
        }else{
            View view = LayoutInflater.from(mContext).inflate(R.layout.chat_item_left, parent, false);
            return new MessageAdapter.ViewHolder(view);
        }
    }

    @Override
    public void onBindViewHolder(@NonNull MessageAdapter.ViewHolder holder, int position) {
        Chat chat = mChat.get(position);

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

        if (imageurl.equals("default")){
            holder.user_profile.setImageResource(R.drawable.profile);
        }else{
            Glide.with(mContext).load(imageurl).into(holder.user_profile);
        }
    }

    @Override
    public int getItemCount() {
        return mChat.size();
    }


    public class ViewHolder extends RecyclerView.ViewHolder{
        public TextView show_message;
        public ImageView user_profile;


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

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


    }

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

    }

}

聊天.java

package com.runyankole.runyankole.runyankole.Model;

public class Chat {
    private String sender;
    private String receiver;
    private String 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;
    }
}

注意：当我单击用户发送聊天时，应用程序与应用程序的冲突已停止。当我签入 logcat 时，我在 logcat 中看到了上述错误。我需要一些帮助。

标签： androidfirebase-realtime-database