RecyclerView 更新而不刷新适配器列表

Question

I am trying to build a chat app and when I want to add a message to my custom RecyclerView, the whole messages get affected and they will change (ESPECIALLY when adding an Image).

I tried to do notifyItemChanged(position) , but it got worse even. Here is my Adapter code:

 @NonNull
@Override
public MessageViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
    View layoutView = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_message, null, false);
    FrameLayout.LayoutParams lp = new FrameLayout.LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT);

    layoutView.setLayoutParams(lp);

    MessageViewHolder rcv = new MessageViewHolder(layoutView);
    return rcv;
}

@Override
public void onBindViewHolder(@NonNull final MessageViewHolder holder, final int position) {


    holder.mMessage.setText(messageList.get(position).getMessage());
    holder.mSender.setText(messageList.get(position).getSenderId());
    Picasso.Builder builder = new Picasso.Builder(context);
    builder.downloader(new OkHttp3Downloader(context));
    builder.build().load(messageList.get(position).getProfilePic())
            .placeholder((R.drawable.image))
            .into(holder.imgprofile);

    if(!messageList.get(holder.getAdapterPosition()).getMediaUrlList().isEmpty()){
        holder.mViewMedia.setVisibility(View.VISIBLE);
        Picasso.Builder builder2 = new Picasso.Builder(context);
        builder2.downloader(new OkHttp3Downloader(context));
        builder2.build().load(messageList.get(holder.getAdapterPosition()).getMediaUrlList().get(0))
                .placeholder((R.drawable.ic_launcher_background))
                .error(R.drawable.ic_launcher_background)
                .into(holder.mViewMedia);

    }


    holder.mViewMedia.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            new ImageViewer.Builder(v.getContext(), messageList.get(holder.getAdapterPosition()).getMediaUrlList())
                    .setStartPosition(0)
                    .show();
        }
    });

}

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





class MessageViewHolder extends RecyclerView.ViewHolder{
   //defining textviews and stuff..
    }
}

I will be happy if anyone has any ideas.

Answer 1

i think there is utility class named DiffUtil present in Android Support Library. It's a callback that detects changes between two Lists.

you can refer some tutorial on it: https://www.journaldev.com/20873/android-recyclerview-diffutil and https://medium.com/@iammert/using-diffutil-in-android-recyclerview-bdca8e4fbb00

Answer 2

Make your class extend ListAdapter . Create a DiffUtil.ItemCallback variable. and pass it to superclass constructor. Rest of the methods will be more or less similar when compared to using RecyclerView.Adapter .

Here's some sample code:

MessageAdapter.java

public class MessageAdapter extends ListAdapter<Model, MessageAdapter.MessageHolder> {
    private static final DiffUtil.ItemCallback<Model> DIFF_CALLBACK = new DiffUtil.ItemCallback<Model>() {
        @Override
        public boolean areItemsTheSame(@NonNull Model oldItem, @NonNull Model newItem) {
            return oldItem.getId() == newItem.getId();
        }

        @Override
        public boolean areContentsTheSame(@NonNull Model oldItem, @NonNull Model newItem) {
            return oldItem.getMessage().equals(newItem.getMessage()) &&
                    oldItem.getSeen().equals(newItem.getSeen()); //and other similar checks
        }
    };

    public MessageAdapter() {
        super(DIFF_CALLBACK);
    }

    @NonNull
    @Override
    public MessageHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View itemView = LayoutInflater.from(parent.getContext()).inflate(R.layout.message_item, parent, false);
        return new MessageHolder(itemView);
    }

    @Override
    public void onBindViewHolder(@NonNull MessageHolder holder, int position) {
        Message currentMessage = getItem(position);
        holder.messageTextview.setText(currentMessage.getMessage());
        holder.seenTextview.setText(currentMessage.getSeen());
        //further views
    }

    public Message getMessageAt(int position) {
        return getItem(position);
    }

    class MessageHolder extends RecyclerView.ViewHolder {
        private TextView messageTextview;
        private TextView seenTextview;
        //other views

        MessageHolder(@NonNull View itemView) {
            super(itemView);
            messageTextview = itemView.findViewById(R.id.message_tv);
            seenTextview = itemView.findViewById(R.id.seen_tv);

            //Register listeners if needed
        }
    }
}

And finally submit your list using this adapter class' object. Like:

MessageAdapter adapter = new MessageAdapter();

//prepare list and submit using
adapter.submitList(list);

areItemsTheSame() should implement the checks which makes sure that the items as whole which are inflated are the same. Whereas, areContentsTheSame() should implement the checks which ensure the content inside each recyclerview item is not changed.

Implementing this automatically takes care of all animations as the DiffUtil class takes care of calculating the difference between lists and you don't have to store any reference in regards to the position at which the object has changed.