java - 如何存储和检索 RecyclerView 项目以供离线使用

Question

伙计们，请不要重复这个问题，因为我在我的应用程序中没有发现任何简单或容易实现的 Realm 。我正在创建一个聊天应用程序，我想做的是让用户即使没有互联网连接也能够访问和阅读他收到的早期消息。

简而言之，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的新手。

以下是我的代码供您阅读:

fragment

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，这就是我的代码。

Answer 1

您可以使用SQLite 数据库 离线存储聊天记录，观看this YouTube tutorial , 它很广泛，但您可以跳过某些部分。

当下载/发送聊天消息时，将它们镜像到您的数据库中，并使用数据库和ONLY THE DATABASE 作为您的 RecyclerView 的数据源(永远不要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，然后在将其放入布局时从数据库中读取)。

为了提高性能，您可以将相关的聊天消息存储在内存中(例如，在单独的 ArrayList 中)而不是总是从刚刚写入的数据库中读取数据.