Question

我正在创建一个聊天应用程序，并且为了显示消息，我正在使用回收站视图。最新消息显示在底部。用户向上滚动以查看更多消息。

加载聊天屏幕后，视图不会从最底部开始，并且最新消息也不可见。用户必须向下滚动几行才能看到最新消息。这是糟糕的用户界面，最新消息应该在屏幕的结尾/底部可见。

我正在使用setReverseLayout(true)和setStackFromEnd(false)，并且我在网上搜索了类似的问题也没有运气。现在，我在延迟设置回收器视图之后立即将滚动位置设置为0，但这并不总是有效，而且很容易。

如果我正常设置了recyclerview（不使用setReverseLayout和setStackFromEnd），则每次都将最新消息完美地加载到顶部。

以下是启动回收站视图的代码：

RecyclerView recyclerView = findViewById(R.id.recyclerViewMessageRoom);
    adapter = new RA_MessageRoom(this, userFirebaseUid, messagesGroupedByDate, messageUsers);
    recyclerView.setAdapter(adapter);

    LinearLayoutManager layoutManager = new LinearLayoutManager(this);
    layoutManager.setReverseLayout(true);
    layoutManager.setStackFromEnd(false);
    recyclerView.setHasFixedSize(true);
    recyclerView.setLayoutManager(layoutManager);

    // -- Workaround with delay - still doesn't completely work
    new Handler().postDelayed(() -> {
        recyclerView.scrollToPosition(0);
    }, 200);

遇到此问题并知道如何解决的任何人，请分享！谢谢。

编辑（2019年7月6日）：

这是回收站适配器的代码。提醒一下，如果我删除反向布局设置，效果会很好。

RA_MessageRoom：

public class RA_MessageRoom extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
private static final String TAG = "RA_MessageRoom";
private static final int TYPE_USER = 1;
private static final int TYPE_PARTICIPANT = 2;

private Context context;
private String userFirebaseUid;
private List<MessagesDateGrouper> messagesGroupedByDate;
private HashSet<MessagesUserModel> messageUsers;

public RA_MessageRoom(Context context, String userFirebaseUid, List<MessagesDateGrouper> messagesGroupedByDate, HashSet<MessagesUserModel> messageUsers) {
    this.context = context;
    this.userFirebaseUid = userFirebaseUid;
    this.messagesGroupedByDate = messagesGroupedByDate;
    this.messageUsers = messageUsers;
}

@Override
public int getItemViewType(int position) {

    if (messagesGroupedByDate.get(position).getViewType() == MessagesDateGrouper.TYPE_CHAT) {
        MessageChatItem message = (MessageChatItem) messagesGroupedByDate.get(position);
        if (message.getMessages().getSenderFirebaseUid().equals(userFirebaseUid)) {
            return TYPE_USER;
        } else {
            return TYPE_PARTICIPANT;
        }
    } else {
        return messagesGroupedByDate.get(position).getViewType();
    }
}


@Override
public int getItemCount() {
    return messagesGroupedByDate != null ? messagesGroupedByDate.size() : 0;
}

@NonNull
@Override
public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
    final RecyclerView.ViewHolder holder;
    View view;

    switch (viewType) {
        case MessagesDateGrouper.TYPE_DATE:
            view = LayoutInflater.from(parent.getContext()).inflate(R.layout.recycler_message_room_separator, parent, false);
            holder = new MessageRoomDateVH(view);
            break;

        case TYPE_USER:
            view = LayoutInflater.from(parent.getContext()).inflate(R.layout.recycler_message_room_user, parent, false);
            holder = new MessageRoomUserVH(view);
            break;

        case TYPE_PARTICIPANT:
            view = LayoutInflater.from(parent.getContext()).inflate(R.layout.recycler_message_room_participant, parent, false);;
            holder = new MessageRoomParticipantVH(view);
            break;

        default:
            view = LayoutInflater.from(parent.getContext()).inflate(R.layout.recycler_message_room_user, parent, false);;
            holder = new MessageRoomUserVH(view);
            break;
    }

    return holder;
}

@Override
public void onBindViewHolder(@NonNull RecyclerView.ViewHolder holder, int position) {
    if (holder instanceof MessageRoomDateVH) {
        MessageDateItem date = (MessageDateItem) messagesGroupedByDate.get(position);
        ((MessageRoomDateVH)holder).date.setText(date.getDate());

    } else if (holder instanceof MessageRoomParticipantVH) {
        MessageRoomParticipantVH view = (MessageRoomParticipantVH) holder;
        MessageChatItem messageItem = (MessageChatItem) messagesGroupedByDate.get(position);
        MessagesModel message = messageItem.getMessages();

        view.name.setText(context.getString(R.string.unknown));
        view.profileImage.setImageResource(R.drawable.default_profile_image_grey);

        for (MessagesUserModel user: messageUsers) {
            if (user.getFirebaseId().equals(message.getSenderFirebaseUid())) {
                int fallbackImage;
                if (user.getMerchant() == null || !user.getMerchant()) {
                    fallbackImage = R.drawable.default_profile_image_grey;
                } else {
                    fallbackImage = R.drawable.store_profile;
                }

                GlideApp.with(context)
                        .load(user.getPhotoThumbUrl())
                        .placeholder(R.drawable.placeholder)
                        .fallback(fallbackImage)
                        .into(view.profileImage);

                view.name.setText(user.getName());
                break;
            }
        }


        if (message.getImageUrl() != null && !message.getImageUrl().equals("") ) {
            view.image.setVisibility(View.VISIBLE);
            view.imageSpinner.setVisibility(View.VISIBLE);
            view.chat.setVisibility(View.GONE);



            view.image.setClipToOutline(true);

            GlideApp.with(context)
                    .load(message.getImageUrl())
                    .placeholder(R.drawable.placeholder_message)
                    .fallback(R.drawable.placeholder_message)
                    .listener(new RequestListener<Drawable>() {
                        @Override
                        public boolean onLoadFailed(@Nullable GlideException e, Object model, Target<Drawable> target, boolean isFirstResource) {
                            return false;
                        }

                        @Override
                        public boolean onResourceReady(Drawable resource, Object model, Target<Drawable> target, DataSource dataSource, boolean isFirstResource) {
                            view.imageSpinner.setVisibility(View.GONE);
                            return false;
                        }
                    })
                    .into(view.image);


        } else {
            view.chat.setVisibility(View.VISIBLE);
            view.image.setVisibility(View.GONE);
            view.imageSpinner.setVisibility(View.GONE);

            view.chat.setText(message.getMessageText());
        }

        String time = DateFormatService.messageRoomParseDateToTimeString(message.getDate());
        view.date.setText(time);

    } else if (holder instanceof MessageRoomUserVH){
        MessageRoomUserVH view = (MessageRoomUserVH) holder;
        MessageChatItem messageItem = (MessageChatItem) messagesGroupedByDate.get(position);
        MessagesModel message = messageItem.getMessages();


        if (message.getImageUrl() != null && !message.getImageUrl().equals("") ) {
            view.image.setVisibility(View.VISIBLE);
            view.imageSpinner.setVisibility(View.VISIBLE);
            view.chat.setVisibility(View.GONE);

            view.image.setClipToOutline(true);

            GlideApp.with(context)
                    .load(message.getImageUrl())
                    .placeholder(R.drawable.placeholder_message)
                    .fallback(R.drawable.placeholder_message)
                    .listener(new RequestListener<Drawable>() {
                        @Override
                        public boolean onLoadFailed(@Nullable GlideException e, Object model, Target<Drawable> target, boolean isFirstResource) {
                            return false;
                        }

                        @Override
                        public boolean onResourceReady(Drawable resource, Object model, Target<Drawable> target, DataSource dataSource, boolean isFirstResource) {
                            view.imageSpinner.setVisibility(View.GONE);
                            return false;
                        }
                    })
                    .into(view.image);


        } else {
            view.chat.setVisibility(View.VISIBLE);
            view.image.setVisibility(View.GONE);
            view.imageSpinner.setVisibility(View.GONE);

            view.chat.setText(message.getMessageText());
        }

        String time = DateFormatService.messageRoomParseDateToTimeString(message.getDate());
        view.date.setText(time);
    }


}

public class MessageRoomDateVH extends RecyclerView.ViewHolder {
    TextView date;

    public MessageRoomDateVH(@NonNull View itemView) {
        super(itemView);
        date = itemView.findViewById(R.id.textMessageRoomDateSection);
    }
}


public class MessageRoomParticipantVH extends RecyclerView.ViewHolder {
    ImageView profileImage;
    TextView name;
    TextView chat;
    ImageView image;
    TextView date;
    ProgressBar imageSpinner;

    public MessageRoomParticipantVH(@NonNull View itemView) {
        super(itemView);

        profileImage = itemView.findViewById(R.id.imageMessageRoomParticipantProfile);
        name = itemView.findViewById(R.id.textMessageRoomParticipantName);
        chat = itemView.findViewById(R.id.textMessageRoomParticipantChat);
        image = itemView.findViewById(R.id.imageMessageRoomParticipantImage);
        date = itemView.findViewById(R.id.textMessageRoomParticipantDate);
        imageSpinner = itemView.findViewById(R.id.progressBarMessageRoomParticipantImage);


    }
}

public class MessageRoomUserVH extends RecyclerView.ViewHolder {
    TextView chat;
    ImageView image;
    TextView date;
    ProgressBar imageSpinner;

    public MessageRoomUserVH(@NonNull View itemView) {
        super(itemView);

        chat = itemView.findViewById(R.id.textMessageRoomUserChat);
        image = itemView.findViewById(R.id.imageMessageRoomUserImage);
        date = itemView.findViewById(R.id.textMessageRoomUserDate);
        imageSpinner = itemView.findViewById(R.id.progressBarMessageRoomUserImage);
    }
}

}

编辑：

尽管首选将stackFromEnd设置为false，但最终还是将stackFromEnd从false更改为true，删除了延迟，并按照接受的答案的建议继续设置滚动位置以解决此问题。

更新代码：

RecyclerView recyclerView = findViewById(R.id.recyclerViewMessageRoom);
    adapter = new RA_MessageRoom(this, userFirebaseUid, messagesGroupedByDate, messageUsers);
    recyclerView.setAdapter(adapter);

    LinearLayoutManager layoutManager = new LinearLayoutManager(this);
    layoutManager.setReverseLayout(true);
    layoutManager.setStackFromEnd(true);
    recyclerView.setHasFixedSize(true);
    recyclerView.setLayoutManager(layoutManager);
    recyclerView.scrollToPosition(0);

感谢您的帮助！

Answer 1

您可以在xml中设置布局管理器并反向布局。当我们设置反向布局时，我们会发现此问题。我们可以通过添加setStackFromEnd = true

来解决它

    app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"
    android:orientation="vertical"
    app:reverseLayout="true"
    app:stackFromEnd="true"

Answer 2

查看此答案：

RecyclerView - Reverse Order

并为您的RA_MessageRoom创建一个setter来更新您的messagesGroupedByDate。像这样：

Collections.reverse(messagesGroupedByDate); // Reverse your dataset like in answer above
adapter.setMessagesGroupedByDate(messagesGroupedByDate); // Update your dataset in adapter
adapter.notifyDataSetChanged(); // Notify your adapter

每次有新消息到达时，您的列表都会更新。您需要将此代码段放入数据提取中，然后才能删除postDelayed处理程序。

Answer 3

这很容易，您只需要添加一行即可：-

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

Answer 4

看起来像一个 bug in recycler view 实现，或者更确切地说是在那个线性布局管理器中。

要解决此问题，您需要确保在您的回收站可以滚动时 stackFromEnd 为 true。如果您的回收商没有足够的项目可供滚动，而您仍希望它们位于屏幕底部，那么如果回收商无法滚动，请将 stackFromEnd 重新设置为 false。

要判断您的视图是否可以滚动，您可以使用 Kotlin 扩展：

/**
 * Tells if this view can scroll vertically.
 * This view may still contain children who can scroll.
 */
fun View.canScrollVertically() = this.let {
    it.canScrollVertically(-1) || it.canScrollVertically(1)
}

在 Fulguris 中，我使用了以下函数来修复该错误，诀窍是找到在代码中调用它的正确位置：

/**
 * Workaround reversed layout bug: https://github.com/Slion/Fulguris/issues/212    
 */
fun fixScrollBug(aList : RecyclerView): Boolean {
    val lm = (aList.layoutManager as LinearLayoutManager)
    // Can't change stackFromEnd when computing layout or scrolling otherwise it throws an exception
    if (!aList.isComputingLayout) {
        if (aList.context.configPrefs.toolbarsBottom) {
            // Workaround reversed layout bug: https://github.com/Slion/Fulguris/issues/212
            if (lm.stackFromEnd != aList.canScrollVertically()) {
                lm.stackFromEnd = !lm.stackFromEnd
                return true
            }
        } else {
            // Make sure this is set properly when not using bottom toolbars
            // No need to check if the value is already set properly as this is already done internally
            lm.stackFromEnd = false
        }
    }

    return false
}

我猜您可以用针对 toolbarsBottom 的检查替换 lm.reverseLayout 上的特定应用检查。

Recyclerview反向布局开始滚动位置问题

4 个答案: