java如何存储和检索RecyclerView项以供脱机使用

Question

伙计们，请不要重复这个问题，因为我还没有在我的应用程序中找到任何简单的领域实现。我正在创建一个聊天应用程序，我想做的是让用户能够访问和阅读他在没有互联网连接的情况下收到的早期消息

简言之，我希望我的应用程序在没有互联网连接的情况下仍然可以访问，但我发现很难做到这一点，因为我是本地数据存储新手

以下是我的代码供您阅读：

片段

public class ChatFragment extends Fragment {

public RecyclerView mChatsList;
public View mView;
public List<ChatsModel> mChatsModel;
public ChatsAdapter mChatsAdapter;
private Realm realm;


public ChatFragment() {
    // Required empty public constructor
}


@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    mView = inflater.inflate(R.layout.fragment_chat, container, false);
    ((AppCompatActivity) getActivity()).getSupportActionBar().setShowHideAnimationEnabled(true);
    initUI();
    realm = Realm.getDefaultInstance();
    return mView;
}

//Method and views initializer
public void initUI() {

    mChatsList = (RecyclerView) mView.findViewById(R.id.chatsList);

    LinearLayoutManager layoutManager = new LinearLayoutManager(getActivity());

    mChatsModel = new ArrayList<ChatsModel>();
    mChatsAdapter = new ChatsAdapter(getActivity(), mChatsModel);
    mChatsList.setLayoutManager(layoutManager);
    mChatsList.setHasFixedSize(true);
    mChatsAdapter.notifyDataSetChanged();
    mChatsList.setAdapter(mChatsAdapter);
    RecyclerView.ItemAnimator itemAnimator = new DefaultItemAnimator();
    itemAnimator.setAddDuration(1000);
    itemAnimator.setRemoveDuration(1000);
    mChatsList.setItemAnimator(itemAnimator);
    prepareItems();

    Realm realm = Realm.getInstance(getActivity());
    realm.executeTransaction(new Realm.Transaction() {
        @Override
        public void execute(Realm realm) {
            ChatsModel chat = realm.createObject(ChatsModel.class);
            chat.setUsername("username");
            chat.setDate("date");
            chat.setPicture("Picture");
        }
    }, new Realm.Transaction.Callback() {
        @Override
        public void onSuccess() {
            Main.Mess(getString(R.string.real_sucess));
        }

        @Override
        public void onError(Exception e) {
            Main.Mess(getString(R.string.real_error));
        }
    });

}



// This is a simple method to add items to our recyclerview
private void prepareItems() {
    Rests mRests = RestService.createService(Rests.class, Session.getToken(getActivity()));
    mRests.suggest(new Callback<List<ChatsModel>>() {
        @Override
        public void success(List<ChatsModel> mChatsModel, Response response) {
            RealmList<ChatsModel> mChatsModel2 = new RealmList<ChatsModel>();
            mChatsAdapter.setUsers(mChatsModel);

        }

        @Override
        public void failure(RetrofitError error) {
            Main.Mess(getString(R.string.server_error));
        }
    });
}

}

我的适配器

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

private static final int TYPE_HEADER = 0;
private static final int TYPE_ITEM = 1;
private RealmList<ChatsModel> mChatsModel;
private Realm realm;
public Activity mActivity;

public ChatsAdapter(@NonNull Activity mActivity) {
    super();
    this.mChatsModel = new RealmList<>();
    this.realm = Realm.getDefaultInstance();
    this.mActivity = mActivity;
}


@Override
public RecyclerView.ViewHolder onCreateViewHolder (ViewGroup parent, int viewType) {
    if(viewType == TYPE_HEADER) {
        View v = LayoutInflater.from (parent.getContext ()).inflate (R.layout.ad_view, parent, false);
        return new HeaderViewHolder (v);
    } else if(viewType == TYPE_ITEM) {
        View v = LayoutInflater.from (parent.getContext ()).inflate (R.layout.chats_item, parent, false);
        return new ContentViewHolder (v);
        }
    return null;
}

private ChatsModel getItem (int position) {
    return mChatsModel.get (position);
}

@Override
public void onBindViewHolder (RecyclerView.ViewHolder holder, final int position) {
    if (holder instanceof HeaderViewHolder) {
        HeaderViewHolder headerHolder = (HeaderViewHolder) holder;
        if (Constant.SHOW_ADS) {
            headerHolder.mAdView.setVisibility(View.VISIBLE);
            AdRequest adRequest = new AdRequest.Builder().build();
            headerHolder.mAdView.loadAd(adRequest);
        } else {
            headerHolder.mAdView.setVisibility(View.GONE);
        }
    }else if (holder instanceof ContentViewHolder) {
        ContentViewHolder contentHolder = (ContentViewHolder) holder;
        ChatsModel item  = getItem (position - 1);

        contentHolder.username.setText(item.getUsername());
        contentHolder.date.setText(item.getDate());
        contentHolder.message.setText(item.getMessage());

        Picasso.with(mActivity.getApplicationContext())
                .load(Constant.IMAGE_SMALL + item.getPicture())
                .error(R.drawable.user)
                .into(contentHolder.picture);
    }
}

@Override
public int getItemViewType (int position) {
    if(isPositionHeader (position)) {
        return TYPE_HEADER;
    }
    return TYPE_ITEM;
}

public void setUsers(RealmList<ChatsModel> friendsItems) {
    this.mChatsModel = friendsItems;
    notifyDataSetChanged();
}

public List<ChatsModel> getSuggestionsModel() {
    return this.mChatsModel;
}

private boolean isPositionHeader (int position) {
    return position == 0;
}


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


public class HeaderViewHolder extends RecyclerView.ViewHolder {
    public AdView mAdView;

    public HeaderViewHolder(View itemView) {
        super(itemView);
        mAdView = (AdView) itemView.findViewById(R.id.ad_view);
    }
}
public class ContentViewHolder extends RecyclerView.ViewHolder {

    public ImageView picture;
    public TextView username, date, message;
    public LinearLayout chat;

    public ContentViewHolder(View v) {
        super(v);
        picture = (ImageView) v.findViewById(R.id.picture);
        username = (TextView) v.findViewById(R.id.username);
        date = (TextView) v.findViewById(R.id.date);
        message = (TextView) v.findViewById(R.id.message);
    }
}
}

好的，这是我的密码

Answer 1

正如@geisshirt在评论中所说，使用RealmRecyclerViewAdapter而不是RecyclerView.Adapter。你可以在official doc中找到关于android领域适配器的几句话

此外，您还可以查看RealmRecyclServiceAdapter example

Answer 2

你可以使用一个SQLite数据库来离线存储聊天，看看this YouTube tutorial，它很广泛，但你可以跳过一些部分

下载/发送聊天信息时，将其镜像到数据库中，并使用数据库，并且仅将数据库用作RecyclerView的数据源（切勿让任何在线数据直接进入列表，始终先将其存储在数据库中，并在将其放入布局时从数据库中读取）

为了提高性能，您可以在内存中存储相关的聊天信息（例如在一个单独的ArrayList中）而不是总是从刚刚写入数据库的数据库中读取数据