如何自动滚动到recyclerView的底部？

Question

我正在制作一个聊天应用程序，我需要滚动到回收站视图的底部以显示最后一条消息。 发这个问题的主要目的是问如何滚动到recyclerView的底部。 我已经在 readMessage() 方法中尝试了下面这行代码，但仍然无法正常工作。

groupChatRecyclerView.smoothScrollToPosition(messageAdapter.getItemCount());

对于recyclerView：groupChatRecyclerView.setHasFixedSize(true);

对于 LinearLayoutManager：

linearLayoutManager = new LinearLayoutManager(getApplicationContext()); linearLayoutManager.setStackFromEnd(true); linearLayoutManager.setReverseLayout(false); groupChatRecyclerView.setLayoutManager(linearLayoutManager);

请问有人可以帮我吗？ 代码：

private void readMessage() {
    mchat = new ArrayList<>();

    reference = groupReference.child("Messages");
    reference.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            mchat.clear();
            for (DataSnapshot snapshot : dataSnapshot.getChildren()){
                GroupChats chat = snapshot.getValue(GroupChats.class);
                mchat.add(chat);

                messageAdapter = new GroupMessageAdapter(GroupMessageActivity.this, mchat, (LayoutInflater) getSystemService(LAYOUT_INFLATER_SERVICE));
                groupChatRecyclerView.setAdapter(messageAdapter);
                //linearLayoutManager.smoothScrollToPosition(groupChatRecyclerView, null, messageAdapter.getItemCount()-1);
               // groupChatRecyclerView.smoothScrollToPosition(messageAdapter.getItemCount());
            }
        }

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

        }
    });

}

GroupMessageAdapter 代码：

package com.example.chats.Adapter;




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

private Context mContext;
public static final int MSG_TYPE_LEFT = 0;
public static final int MSG_TYPE_RIGHT = 1;
public static final int MSG_TYPE_IMAGE_LEFT = 2;
public static final int MSG_TYPE_IMAGE_RIGHT = 3;
private List<GroupChats> mChat;
FirebaseUser fuser;
LayoutInflater inflater;
DatabaseReference userRef = FirebaseDatabase.getInstance().getReference("Users");

public GroupMessageAdapter(Context mContext, List<GroupChats> mChat, LayoutInflater inflater) {
    this.mContext = mContext;
    this.mChat = mChat;
    this.inflater = inflater;
}

@NonNull
@Override
public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
    RecyclerView.ViewHolder viewHolder = null;
    inflater = LayoutInflater.from(parent.getContext());

    switch (viewType){
        case MSG_TYPE_LEFT:
            View textOnlyLViewHolder = inflater.inflate(R.layout.group_item_left, parent,false);
            viewHolder = new LeftMessageG(textOnlyLViewHolder);
            break;
        case MSG_TYPE_RIGHT:
            View textOnlyRViewHolder = inflater.inflate(R.layout.chat_item_right, parent,false);
            viewHolder = new RightMessageG(textOnlyRViewHolder);
            break;
        case MSG_TYPE_IMAGE_LEFT:
            View imageOnlyLViewHolder = inflater.inflate(R.layout.group_image_left, parent,false);
            viewHolder = new LeftImageG(imageOnlyLViewHolder);
            break;
        case MSG_TYPE_IMAGE_RIGHT:
            View imageOnlyRViewHolder = inflater.inflate(R.layout.image_right, parent,false);
            viewHolder = new RightImageG(imageOnlyRViewHolder);
            break;
        default:
    }

    return viewHolder;
}

@Override
public void onBindViewHolder(@NonNull RecyclerView.ViewHolder holder, int position) {

    GroupChats chat = mChat.get(position);

    try{

        String mess = chat.getMessage();

        userRef.child(chat.getSender()).addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot snapsh) {
                if (snapsh.exists()){
                    final String userImage = snapsh.child("imageURL").getValue().toString();


                    switch (holder.getItemViewType()){
                        case MSG_TYPE_RIGHT:
                            RightMessageG rightM = (RightMessageG) holder;
                            rightM.show_messageR.setText(mess);
                            rightM.show_messageR.setOnClickListener(new View.OnClickListener() {
                                @Override
                                public void onClick(View v) {
                                    Toast.makeText(mContext, mess, Toast.LENGTH_SHORT).show();
                                }
                            });
                            rightM.text_seen.setVisibility(View.INVISIBLE);
                            break;
                        case MSG_TYPE_LEFT:
                            LeftMessageG leftM = (LeftMessageG) holder;
                            leftM.show_messageL.setText(mess);
                            Glide.with(mContext).load(userImage).into(leftM.photoGMember);
                            break;
                        case MSG_TYPE_IMAGE_RIGHT:
                            RightImageG rightI = (RightImageG) holder;
                            rightI.text_seen.setVisibility(View.INVISIBLE);
                            rightI.show_imageR.setOnClickListener(new View.OnClickListener() {
                                @Override
                                public void onClick(View v) {
                                    Intent intent = new Intent(mContext, FullImage.class);
                                    intent.putExtra("image", mess);
                                    mContext.startActivity(intent);
                                }
                            });
                            Glide.with(rightI.show_imageR).load(mess).into(rightI.show_imageR);
                            break;
                        case MSG_TYPE_IMAGE_LEFT:
                            LeftImageG leftI = (LeftImageG) holder;
                            Glide.with(mContext).load(userImage).into(leftI.photoGMember);
                            Glide.with(mContext).load(mess).into(leftI.show_imageL);
                            break;
                    }
                }
            }

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

            }
        });

    }catch (Exception e){

    }

}

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

@Override
public int getItemViewType(int position) {
    fuser = FirebaseAuth.getInstance().getCurrentUser();

    if (mChat.get(position).getSender().equals(fuser.getUid())){
        if (mChat.get(position).getType().equals("text")){
            return MSG_TYPE_RIGHT;
        }else {
            return MSG_TYPE_IMAGE_RIGHT;
        }

    }
    else {
        if (mChat.get(position).getType().equals("text")){
            return MSG_TYPE_LEFT;
        }else {
            return MSG_TYPE_IMAGE_LEFT;
        }
    }
}

public class LeftMessageG extends RecyclerView.ViewHolder{
    public TextView show_messageL;
    public CircleImageView text_seen,photoGMember;

    public LeftMessageG(@NonNull View itemView) {
        super(itemView);
        show_messageL = itemView.findViewById(R.id.show_messageLL);
        text_seen = itemView.findViewById(R.id.text_seen);
        photoGMember = itemView.findViewById(R.id.photoGMember);
    }
}

public class RightMessageG extends RecyclerView.ViewHolder{
    public TextView show_messageR;
    public CircleImageView text_seen;

    public RightMessageG(@NonNull View itemView) {
        super(itemView);
        show_messageR = itemView.findViewById(R.id.show_messageR);
        text_seen = itemView.findViewById(R.id.text_seen);
    }
}

public class RightImageG extends RecyclerView.ViewHolder{
    public ImageView show_imageR;
    public CircleImageView text_seen;

    public RightImageG(@NonNull View itemView) {
        super(itemView);
        show_imageR = itemView.findViewById(R.id.show_imageR);
        text_seen = itemView.findViewById(R.id.text_seen);
    }
}

public class LeftImageG extends RecyclerView.ViewHolder{
    public ImageView show_imageL;
    public CircleImageView text_seen, photoGMember;

    public LeftImageG(@NonNull View itemView) {
        super(itemView);
        show_imageL = itemView.findViewById(R.id.show_imageL);
        text_seen = itemView.findViewById(R.id.text_seen);
        photoGMember = itemView.findViewById(R.id.photoGMember);
    }
}

}

Answer 1

试试这个

groupChatRecyclerView.smoothScrollToPosition(groupChatRecyclerView.getAdapter().getItemCount() - 1);

Answer 2

在你的 readMessage 函数中添加这个

groupChatRecyclerView.scrollToPosition(mchat.size - 1);

滚动到添加到 RecyclerView 的最后一项。