Android Architecture Components如何结合数据库和网络中的LiveData？

Question

There's an example provided in NetworkBoundResource, but when I tried it out, if database returns a result, it does not fetch from network anymore. What I want is display data from database and trigger network at the same time and eventually replace data in database after network completes. Example codes will be much appreciated.

Answer 1

I would use room database to save your items in a table. Then you use Paging list to observe to that table. The first time you observe to that table, also do a request to network. When you receive the response delete all items from the table and insert the new ones (all this in a repository class, and in a background thread). This last step will update your paging list automatically as your paging list is observing to that room table.

Answer 2

Guess this article could be helpful: https://proandroiddev.com/the-missing-google-sample-of-android-architecture-components-guide-c7d6e7306b8f

and the GitHub repo for this article: https://github.com/PhilippeBoisney/GithubArchitectureComponents

The heart of this solution is UserRepository:

public LiveData<User> getUser(String userLogin) {
        refreshUser(userLogin); // try to refresh data if possible from Github Api
        return userDao.load(userLogin); // return a LiveData directly from the database.
    }

    // ---

    private void refreshUser(final String userLogin) {
        executor.execute(() -> {
            // Check if user was fetched recently
            boolean userExists = (userDao.hasUser(userLogin, getMaxRefreshTime(new Date())) != null);
            // If user have to be updated
            if (!userExists) {
                webservice.getUser(userLogin).enqueue(new Callback<User>() {
                    @Override
                    public void onResponse(Call<User> call, Response<User> response) {
                        Toast.makeText(App.context, "Data refreshed from network !", Toast.LENGTH_LONG).show();
                        executor.execute(() -> {
                            User user = response.body();
                            user.setLastRefresh(new Date());
                            userDao.save(user);
                        });
                    }

                    @Override
                    public void onFailure(Call<User> call, Throwable t) { }
                });
            }
        });
    }