我有一个聊天应用程序作为我的 Android 应用程序的一部分,它将聊天室中的所有消息存储在 Firebase 数据库引用下,该数据库引用包含该房间的 ID 号。就目前而言,保存聊天 Activity 中消息的 RecyclerView 会在用户进入聊天室时下载该房间中的所有消息,从而消耗大量数据。如果用户滚动到顶部,我应该如何让它只下载 X 条最新消息并再下载 X 条消息?
这是我的适配器:
public class ChatRecyclerViewAdapter extends RecyclerView.Adapter<ChatRecyclerViewAdapter.ViewHolder> {
private static final String TAG = "ChatRecyclerViewAdapter";
private String mRoomID;
private Context mContext;
private DatabaseReference mDatabaseReference;
private ArrayList<Message> messageList;
private ChildEventListener mListener = new ChildEventListener() {
@Override
public void onChildAdded(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {
// Convert data snapshot from Database into a Message Object
Message message = dataSnapshot.getValue(Message.class);
// Add it to an arrayList of Messages
messageList.add(message);
// Notice Changes
notifyItemInserted(messageList.size());
}
@Override
public void onChildChanged(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {
}
@Override
public void onChildRemoved(@NonNull DataSnapshot dataSnapshot) {
}
@Override
public void onChildMoved(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
}
};
public ChatRecyclerViewAdapter(Context mContext, ArrayList<String> mMessage, ArrayList<String> mAuthor, String mRoomID, DatabaseReference reference) {
this.mContext = mContext;
this.mRoomID = mRoomID;
messageList = new ArrayList<>();
mDatabaseReference = reference.child(mRoomID+"_messages");
mDatabaseReference.addChildEventListener(mListener);
}
@NonNull
@Override
public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
//This method loads layout(fields) of ViewHolder
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.chat_msg_row,parent, false);
ViewHolder holder = new ViewHolder(view);
return holder;
}
@Override
public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
// This method fills fields with data for each list item
Log.d(TAG,"onBindViewHolder called");
Message message = messageList.get(position);
holder.message.setText(message.getMessage());
holder.author.setText(message.getAuthor()+":");
}
@Override
public int getItemCount() {
return messageList.size();
}
//Viewholder stores the information about the layout and content of each list item, and serves as a template for each item of a RecyclerView
public class ViewHolder extends RecyclerView.ViewHolder {
TextView author;
TextView message;
RelativeLayout singleMessageContainer;
public ViewHolder(View itemView) {
super(itemView);
author = itemView.findViewById(R.id.chatAuthor);
message = itemView.findViewById(R.id.chatMessage);
singleMessageContainer = itemView.findViewById(R.id.singleMessageContainer);
}
}
void cleanup() {
mDatabaseReference.removeEventListener(mListener);
}
}
最佳答案
如果消息已经按时间顺序存储(例如,如果您使用 push()
来添加它们),您可以通过它们的键对消息进行排序并获取最新消息:
mDatabaseReference = reference.child(mRoomID+"_messages");
Query recentMessages = mDatabaseReference.orderByKey().limitToLast(10);
recentMessages.addChildEventListener(mListener);
正如 Doug 评论的那样,请查看 Firebase documentation on queries更多选择
关于java - 在 Firebase 中仅下载部分数据库引用?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/52246539/