如何观察 LiveData，然后将此数据传递给我的适配器？

Question

I have a Calendar . To create this I have a CalendarFragment which opens CustomCalendarView

(a class which extends LinearLayout).

This then uses MyGridAdapter (class which extends ArrayAdapter) to construct the calendar.

When you click a cell on the calendar, you are taken to a new activity in which you can save a log containing some info (and the date of the cell in the calendar which was clicked).

I have a query in my Dao class: Log_Entries_Dao which is passed to LogEntriesRepository and then LogEntriesViewModel .

The Query:

@Query("SELECT date FROM log_entries_table WHERE log_entries_table.date =:date " ) LiveData<List<LogDates>> getAllDatesWithLogs(List<Date> date);

The query receives a list of all dates of the calendar month and then returns a list of all the dates in which a logEntry is present.

Now i would like to observe this LiveData in my setupCalendar method and pas the list of dates in which a logEntry is present to my gridAdater class so I can add circles to all of the cells in which a logEntry is present.

The trouble is, I believe that it is bad practice to use my LogViewModel class inside CustomCalendarView (LinearLayout class). How could correctly query my database, observe the liveData and send this to my adapter from inside my setUpCalendar method?

Calendar Fragment

public class CalendarFragment extends Fragment {

    CustomCalendarView customCalendarView;
    List<Date> dates = new ArrayList<>();
    LogEntriesViewModel logEntriesViewModel;

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        return inflater.inflate(R.layout.calendar_activity_main, container,false);
    }

    @Override
    public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
        customCalendarView =(CustomCalendarView) getView().findViewById(R.id.custom_calendar_view);
        ((AppCompatActivity) getActivity()).getSupportActionBar().hide();
    }
}

CustomCalendarView

public class CustomCalendarView extends LinearLayout {
    ImageButton NextButton, PreviousButton;
    TextView CurrentDate;
    GridView gridView;
    public static final int MAX_CALENDAR_DAYS = 42;
    Calendar calendar = Calendar.getInstance(Locale.ENGLISH);
    Context context;
    MyGridAdapter myGridAdapter;
    SimpleDateFormat dateFormat = new SimpleDateFormat("MMMM yyyy", Locale.ENGLISH);
    SimpleDateFormat monthFormat = new SimpleDateFormat("MMMM", Locale.ENGLISH);
    SimpleDateFormat yearFormat = new SimpleDateFormat("yyyy", Locale.ENGLISH);
    SimpleDateFormat eventDateFormat = new SimpleDateFormat(("dd-MM-yyyy"), Locale.ENGLISH);

    public static final String MY_PREFS_NAME = "MyPrefsFile";

    List<Date> dates = new ArrayList<>();
    List<Log_Entries> eventsList = new ArrayList<>();

    public CustomCalendarView(Context context) {
        super(context);
    }

    public CustomCalendarView(final Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        this.context = context;
        InitializeLayout();
        SetUpCalendar();

        PreviousButton.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                calendar.add(Calendar.MONTH, -1);
                SetUpCalendar();
            }
        });

        NextButton.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                calendar.add(Calendar.MONTH, 1);
                SetUpCalendar();
            }
        });


        gridView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                AlertDialog.Builder builder = new AlertDialog.Builder(context);
                builder.setCancelable(true);

                final String date = eventDateFormat.format(dates.get(position));


                Intent i = new Intent(getContext(), WorkoutButtonsActivity.class);
                i.putExtra(WorkoutButtonsActivity.EXTRA_DATE, date);
                getContext().startActivity(i);
            }
        });
    }

    public CustomCalendarView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    private void InitializeLayout() {
        LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        View view = inflater.inflate(R.layout.calendar_layout, this);
        NextButton = view.findViewById(R.id.nextBtn);
        PreviousButton = view.findViewById(R.id.previousBtn);
        CurrentDate = view.findViewById(R.id.current_Date);
        gridView = view.findViewById(R.id.gridview);
    }

    private void SetUpCalendar() {

        String currentDate = dateFormat.format(calendar.getTime());
        CurrentDate.setText(currentDate);
        dates.clear();
        Calendar monthCalendar = (Calendar) calendar.clone();
        monthCalendar.set(Calendar.DAY_OF_MONTH, 1);
        int FirstDayofMonth = monthCalendar.get(Calendar.DAY_OF_WEEK) - 1;
        monthCalendar.add(Calendar.DAY_OF_MONTH, -FirstDayofMonth);

        while (dates.size() < MAX_CALENDAR_DAYS) {
            dates.add(monthCalendar.getTime());
            monthCalendar.add(Calendar.DAY_OF_MONTH, 1);


        }
        myGridAdapter = new MyGridAdapter(context, dates, calendar, eventsList);
        gridView.setAdapter(myGridAdapter);

    }
}

MyGridAdapter

public class MyGridAdapter extends ArrayAdapter {
    List<Date> dates;
    Calendar currentDate;

    List<Log_Entries> logs;

    LayoutInflater inflater;

    public MyGridAdapter(@NonNull Context context, List<Date> dates, Calendar currentDate, List<Log_Entries> logs){
        super(context, R.layout.single_cell_layout);

        this.dates = dates;
        this.currentDate = currentDate;
        this.logs = logs;
        inflater = LayoutInflater.from(context);

        Log.i("dates", String.valueOf(dates));

    }
    @NonNull
    @Override
    public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
        Date monthDate = dates.get(position);
        Calendar dateCalendar = Calendar.getInstance();
        dateCalendar.setTime(monthDate);
        int DayNo = dateCalendar.get(Calendar.DAY_OF_MONTH);
        int displayMonth = dateCalendar.get(Calendar.MONTH) +1;
        int displayYear = dateCalendar.get(Calendar.YEAR);
        int currentMonth = currentDate.get(Calendar.MONTH) + 1;
        int currentYear = currentDate.get(Calendar.YEAR);
        int currentDay = currentDate.get(Calendar.DAY_OF_MONTH);



        View view = convertView;
        if (view == null){
            view = inflater.inflate(R.layout.single_cell_layout, parent,false);
        }

        if (displayMonth == currentMonth && displayYear == currentYear){
            view.setBackgroundColor(getContext().getResources().getColor(R.color.green));
        }
        else{
            view.setBackgroundColor(Color.parseColor("#cccccc"));
        }

        TextView Day_Number = view.findViewById(R.id.calendar_day);
        Day_Number.setText(String.valueOf(DayNo));

        Calendar eventCalendar = Calendar.getInstance();

        if(DayNo == currentDay && displayMonth == eventCalendar.get(Calendar.MONTH) + 1 && displayYear == eventCalendar.get(Calendar.YEAR)){
            Day_Number.setTextColor(Color.parseColor("#FFFF33"));

        }


        ArrayList<String> arrayList = new ArrayList<>();
        for (int i = 0; i < logs.size(); i++){
        }
        return view;
    }

    @Override
    public int getCount() {
        return dates.size();
    }

    @Override
    public int getPosition(@Nullable Object item) {
        return dates.indexOf(item);
    }

    @Nullable
    @Override
    public Object getItem(int position) {
        return dates.get(position);
    }
}

LogEntriesRepository

public class LogEntriesRepository {

    private Log_Entries_Dao log_entries_dao;
    private LiveData<List<Log_Entries>> allLogEntries;
    private LiveData<List<Log_Entries>> allWorkoutLogEntries;

    private LiveData<List<LogDates>> allDatesWithLog;

    public LogEntriesRepository(Application application) {
        ExerciseDatabase database = ExerciseDatabase.getInstance(application);
        log_entries_dao = database.log_entries_dao();
        allLogEntries = log_entries_dao.getAllFromLogEntries();
    }

    public void insert(Log_Entries log_entries) {
        new InsertLogEntryAsyncTask(log_entries_dao).execute(log_entries);
    }

    public void update(Log_Entries log_entries) {
        new UpdateLogEntryAsyncTask(log_entries_dao).execute(log_entries);
    }

    public void delete(Log_Entries log_entries) {
        new DeleteLogEntryAsyncTask(log_entries_dao).execute(log_entries);
    }


    public LiveData<List<Log_Entries>> getAllLogEntries() {
        return allLogEntries;
    }

    public LiveData<List<Log_Entries>> getAllWorkoutLogEntries(int junctionID, String date) {
        allWorkoutLogEntries = log_entries_dao.getAllFromWorkoutLogEntries(junctionID, date);
        return allWorkoutLogEntries;
    }

    public LiveData<List<LogDates>> getAllDateLogEntries(List<String> date) {
        allDatesWithLog = log_entries_dao.getAllDatesWithLogs(date);
        return allDatesWithLog;
    }

    private static class InsertLogEntryAsyncTask extends AsyncTask<Log_Entries, Void, Void> {
        private Log_Entries_Dao log_entries_dao;

        private InsertLogEntryAsyncTask(Log_Entries_Dao log_entries_dao) {
            this.log_entries_dao = log_entries_dao;
        }

        @Override
        protected Void doInBackground(Log_Entries... log_entries) {
            log_entries_dao.insert(log_entries[0]);
            return null;
        }
    }

    private static class UpdateLogEntryAsyncTask extends AsyncTask<Log_Entries, Void, Void> {
        private Log_Entries_Dao log_entries_dao;

        private UpdateLogEntryAsyncTask(Log_Entries_Dao log_entries_dao) {
            this.log_entries_dao = log_entries_dao;
        }

        @Override
        protected Void doInBackground(Log_Entries... log_entries) {

            log_entries_dao.update(log_entries[0]);
            return null;
        }
    }

    private static class DeleteLogEntryAsyncTask extends AsyncTask<Log_Entries, Void, Void> {
        private Log_Entries_Dao log_entries_dao;

        private DeleteLogEntryAsyncTask(Log_Entries_Dao log_entries_dao) {
            this.log_entries_dao = log_entries_dao;
        }

        @Override
        protected Void doInBackground(Log_Entries... log_entries) {
            log_entries_dao.delete(log_entries[0]);
            return null;
        }
    }

}

LogEntriesViewModel

public class LogEntriesViewModel extends AndroidViewModel {

    private LogEntriesRepository repository;
    private LiveData<List<Log_Entries>> allLogEntries;
    private LiveData<List<Log_Entries>> allWorkoutLogEntries;

    private LiveData<List<LogDates>> allDateLogEntries;


    public LogEntriesViewModel(@NonNull Application application) {
        super(application);
        repository = new LogEntriesRepository(application);
        allLogEntries = repository.getAllLogEntries();
    }


    public void insert(Log_Entries log_entries){
        repository.insert(log_entries);
    }
    public void update(Log_Entries log_entries){
        repository.update(log_entries);
    }
    public void delete(Log_Entries log_entries ) {
        repository.delete(log_entries);
    }
   // public LiveData<List<Log_Entries>> getAllLogs(){
   //     return allLogEntries;
   // }

    public LiveData<List<Log_Entries>> getAllWorkoutLogEntries(int junctionID, String date){
        allWorkoutLogEntries = repository.getAllWorkoutLogEntries(junctionID, date);
        return allWorkoutLogEntries;
    }

    public LiveData<List<LogDates>> getAllDateLogEntries(List<String> date){
        allDateLogEntries = repository.getAllDateLogEntries(date);
        return allDateLogEntries;
    }

}

Answer 1

Try this general schema:

1. Since you Room-method has function with parameter that could be changed during Fragment lifecycle - in your ViewModel should be two Live-data fields instead of one. First, immutable (LiveData) - you'll get result there from your repository. Second, mutable (MutableLiveData) should hold list of your dates (that are visible one your calendar). Then you should use Transfromation.switchMap to make MutableLiveData to be a source for immutable one. Explanation to this method you can read in this answer for example.
2. You should set value of your MutableLiveData from your Fragment (you can do it even from inside your CustomCalendarView since it holds the reference to your Fragment's context. That means that it has an access to ViewModel as well). So at the moment when current month in your Calendar sets or changes (maybe you can add some method changeMonth() there?), you should set new value of your MutableLiveData and... wait for Room's LiveData response.
3. In your Fragment onViewCreated() you should observe your immutable LiveData value and getting it - to invoke method setupCalendar() of your CustomCalendarView (since you have an access to it) and put there your Room's given dates list. It is important to set value of MutableLiveData before you start to observe your LiveData value. To be clear - I propose to change (setup) your calendar view after getting value from Room. But there could be other ways, it's a matter of taste.
4. Next steps (setting list to adapter inside your CustomCalendarView and drawing circles inside your Views) I think you know how to implement.

I hope it can help

Answer 2

I hope if you understand this and apply to your code, That will solve your query if i'm not wrong. i didn't went through all of your code but i get your query which is "How to set Livedata to adapter" and here is the solution for that.

Here the reference code you can compare with yours.

   @Dao
 interface UserDao {
 @Query("SELECT * FROM user ORDER BY lastName ASC")
 public abstract LiveData<List<User>> usersByLastName();
 }

 class MyViewModel extends ViewModel {
 public final LiveData<List<User>> usersList;
 public MyViewModel(UserDao userDao) {
     usersList = userDao.usersByLastName();
 }
 }

 class MyActivity extends AppCompatActivity {
 @Override
 public void onCreate(Bundle savedState) {
     super.onCreate(savedState);
     MyViewModel viewModel = new ViewModelProvider(this).get(MyViewModel.class);
     RecyclerView recyclerView = findViewById(R.id.user_list);
     UserAdapter<User> adapter = new UserAdapter();
     viewModel.usersList.observe(this, list -> adapter.submitList(list));
     recyclerView.setAdapter(adapter);
 }
 }

 class UserAdapter extends ListAdapter<User, UserViewHolder> {
 public UserAdapter() {
     super(User.DIFF_CALLBACK);
 }
 @Override
 public void onBindViewHolder(UserViewHolder holder, int position) {
     holder.bindTo(getItem(position));
 }
 public static final DiffUtil.ItemCallback<User> DIFF_CALLBACK =
         new DiffUtil.ItemCallback<User>() {
     @Override
     public boolean areItemsTheSame(
             @NonNull User oldUser, @NonNull User newUser) {
         // User properties may have changed if reloaded from the DB, but ID is fixed
         return oldUser.getId() == newUser.getId();
     }
     @Override
     public boolean areContentsTheSame(
             @NonNull User oldUser, @NonNull User newUser) {
         // NOTE: if you use equals, your object must properly override 
Object#equals()
         // Incorrectly returning false here will result in too many animations.
         return oldUser.equals(newUser);
     }
  }
}

In Summary,

Step 1 In your Dao:

 public abstract LiveData<List<User>> usersByLastName();

Step 2 In your ViewModel:

public final LiveData<List<User>> usersList;
usersList = userDao.usersByLastName();

And Finally in your Activity/Fragment:

 UserAdapter<User> adapter = new UserAdapter();
 viewModel.usersList.observe(this, list -> adapter.submitList(list));
 recyclerView.setAdapter(adapter);