課題3 ClockViewModel

3-1.java

import android.app.Application;
import android.arch.lifecycle.AndroidViewModel;
import android.arch.lifecycle.LiveData;
import android.arch.lifecycle.MutableLiveData;
import android.support.annotation.NonNull;

import java.util.Date;

public class ClockViewModel extends AndroidViewModel {
    private MutableLiveData<Date> clock;
    public ClockViewModel(@NonNull Application application) {
        super(application);
    }
    public LiveData<Date> getClock() {
        if (clock == null) {
            clock = new ClockLiveData(getApplication());
        }
        return clock;
    }
}