具有不同类型和适配器的RecyclerView [英] RecyclerView with different types and different adapter

问题描述

并感谢您对我的要求的关注. 我是Andorid Studio的新手，正在开发一个App，它必须显示事件，课程和新闻的列表.有一个DrawerLayout，它允许导航到Event，Course和News的区域，每个区域都有每个特定的RecyclerView，但是到home活​​动中，我必须显示所有项目(Event，Course和News). 我为每个项目创建了一个适配器(因为它们具有不同的属性)，并且每个部分(片段)都可以正常工作，但是现在我陷入了主要活动(家庭)中.

and thank you for your attention to my request. I'm a newbie on Andorid Studio and I'm developing an App, it has to show a list of Events, Courses and News. There is a DrawerLayout which allow navigating into Event's, course's and news's area, each area has each specific RecyclerView, but into the home activity, I have to show all the items (Event, Course and News). I create an Adapter for each item (because they have different properties) and each section (fragment) works properly but now I'm stuck with the main activity (the home).

以下是解释它们之间差异的模型: 活动

Here are the models for explaining the difference between them: Event

public class Event {

    private int id;
    private String title;
    private String description;
    private LocalDateTime startingDate;
    private LocalDateTime endingDate;
    private String cost;
    private String website;
    private Category category;
    private Venue venue;
    private Organizer organizer;
    private String status;
    private int resImage;

    public Event(int id, String title, String description, LocalDateTime startingDate, LocalDateTime endingDate, String cost, String website, Category category, Venue venue, Organizer organizer, int image) {
        this.id = id;
        this.title = title;
        this.description = description;
        this.startingDate = startingDate;
        this.endingDate = endingDate;
        this.cost = cost;
        this.website = website;
        this.category = category;
        this.venue = venue;
        this.organizer = organizer;
        this.resImage = image;
    }

    public Event(){}

    public int getId() {
        return id;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String name) {
        this.title = title;
    }

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }

    public LocalDateTime getStartingDate() {
        return startingDate;
    }

    public void setStartingDate(LocalDateTime startingDate) {
        this.startingDate = startingDate;
    }

    public LocalDateTime getEndingDate() {
        return endingDate;
    }

    public void setEndingDate(LocalDateTime endingDate) {
        this.endingDate = endingDate;
    }

    public String getCost() {
        return cost;
    }

    public void setCost(String cost) {
        this.cost = cost;
    }

    public String getWebsite() {
        return website;
    }

    public void setWebsite(String website) {
        this.website = website;
    }

    public Category getCategory() {
        return category;
    }

    public Venue getVenue() {
        return venue;
    }

    public Organizer getOrganizer() {
        return organizer;
    }

    public String getStatus() {
        return status;
    }

    public int getResImage() {
        return resImage;
    }
}

新闻:

public class News {

    private int id;
    private String title;
    private String content;
    private int resImage;

    public News(int id, String title, String content, int image) {
        this.id = id;
        this.title = title;
        this.content = content;
        this.resImage = image;
    }

    public News(){}

    public int getId(){
        return this.id;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getContent() {
        return content;
    }

    public void setDescription(String description) {
        this.content = content;
    }

    public int getResImage() {
        return resImage;
    }

    public void setResImage(int resImage) {
        this.resImage = resImage;
    }

}

课程

public Course(int id, String title, String content, float price, LocalDate startingDate, int availablePlace, Teacher teacher, CourseCategory courseCategory, Location location, Duration duration, Level level, int resImage) {
        this.id = id;
        this.title = title;
        this.content = content;
        this.price = price;
        this.startingDate = startingDate;
        this.availablePlace = availablePlace;
        this.teacher = teacher;
        this.courseCategory = courseCategory;
        this.location = location;
        this.duration = duration;
        this.level = level;
        this.resImage = resImage;
    }

    public int getId() {
        return id;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getContent() {
        return content;
    }

    public void setContent(String content) {
        this.content = content;
    }

    public float getPrice() {
        return price;
    }

    public void setPrice(float price) {
        this.price = price;
    }

    public LocalDate getStartingDate() {
        return startingDate;
    }

    public void setStartingDate(LocalDate startingDate) {
        this.startingDate = startingDate;
    }

    public int getAvailablePlace() {
        return availablePlace;
    }

    public void setAvailablePlace(int availablePlace) {
        this.availablePlace = availablePlace;
    }

    public Teacher getTeacher() {
        return teacher;
    }

    public void setTeacher(Teacher teacher) {
        this.teacher = teacher;
    }

    public CourseCategory getCourseCategory() {
        return courseCategory;
    }

    public void setCourseCategory(CourseCategory courseCategory) {
        this.courseCategory = courseCategory;
    }

    public Location getLocation() {
        return location;
    }

    public void setLocation(Location location) {
        this.location = location;
    }

    public Duration getDuration() {
        return duration;
    }

    public void setDuration(Duration duration) {
        this.duration = duration;
    }

    public Level getLevel() {
        return level;
    }

    public int getResImage() {
        return resImage;
    }

    public void setResImage(int resImage) {
        this.resImage = resImage;
    }
}

这里是适配器: EventAdapter

Here is the Adapters: EventAdapter

public class EventViewAdapter extends RecyclerView.Adapter<EventViewAdapter.EventViewHolder> {

    ArrayList<Event> eventList;
    Context context;

    public EventViewAdapter(ArrayList<Event> eventList, Context context) {
        this.eventList = eventList;
        this.context = context;
    }

    public EventViewAdapter() {
    }

    public static class EventViewHolder extends RecyclerView.ViewHolder {

        ImageView eventImage;
        TextView startingDate, place, title;
        LinearLayout cellLayout;

        EventViewHolder(View eventView) {
            super(eventView);
            eventImage = eventView.findViewById(R.id.event_image);
            startingDate = eventView.findViewById(R.id.event_starting_date);
            place = eventView.findViewById(R.id.event_place);
            title = eventView.findViewById(R.id.event_title);
            cellLayout = eventView.findViewById(R.id.event_cell_layout);
        }
    }

    @NonNull
    @Override
    public EventViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.event_cell_def, parent, false);
        EventViewHolder evh = new EventViewHolder(view);
        return evh;
    }

    @Override
    public void onBindViewHolder(@NonNull EventViewHolder holder, int position) {
        final String title = eventList.get(position).getTitle();
        final String description = eventList.get(position).getDescription();
        final String place = eventList.get(position).getVenue().getCity();
        final String address = eventList.get(position).getVenue().getAddress();
        final String startDate = String.valueOf(eventList.get(position).getStartingDate().toLocalDate());
        final String startTime = String.valueOf(eventList.get(position).getStartingDate().getHour() + ":" + String.valueOf(eventList.get(position).getStartingDate().getMinute()));
        final String endDate = String.valueOf(eventList.get(position).getEndingDate().toLocalDate());
        final String cost = eventList.get(position).getCost();
        final String website = eventList.get(position).getWebsite();
        final String category = eventList.get(position).getCategory().getName();
        final String organizer = eventList.get(position).getOrganizer().getOrganizer();
        final String organizerWebsite = eventList.get(position).getOrganizer().getWebsite();
        final int image = eventList.get(position).getResImage();

        holder.eventImage.setImageResource(image);
        holder.startingDate.setText(startDate);
        holder.place.setText(place);
        holder.title.setText(title);

        holder.cellLayout.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(v.getContext(), DetailEventActivity.class);
                intent.putExtra("title", title);
                intent.putExtra("description", description);
                intent.putExtra("place", place);
                intent.putExtra("address", address);
                intent.putExtra("startDate", startDate);
                intent.putExtra("startTime", startTime);
                intent.putExtra("endDate", endDate);
                intent.putExtra("cost", cost);
                intent.putExtra("website", website);
                intent.putExtra("category", category);
                intent.putExtra("organizer", organizer);
                intent.putExtra("orgWebsite", organizerWebsite);
                intent.putExtra("image", image);

                v.getContext().startActivity(intent);
                Toast.makeText(context, "Hai premuto su: " + title, Toast.LENGTH_SHORT).show();
            }
        });
    }

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

    public void eventSetSearchOperation(ArrayList<Event> newList){
        eventList = new ArrayList<>();
        eventList.addAll(newList);
        notifyDataSetChanged();
    }
}

CourseAdapter:

CourseAdapter:

public class CourseViewAdapter extends RecyclerView.Adapter<CourseViewAdapter.CourseViewHolder> {

    ArrayList<Course> courseList;
    Context context;

    public CourseViewAdapter(ArrayList<Course> courseList, Context context) {
        this.courseList = courseList;
        this.context = context;
    }

    public CourseViewAdapter(){}

    public static class CourseViewHolder extends RecyclerView.ViewHolder {

        ImageView courseImage;
        TextView startingDate, place, title;
        LinearLayout courseLinear;

        CourseViewHolder(View courseView){
            super(courseView);
            courseImage = courseView.findViewById(R.id.course_image);
            startingDate = courseView.findViewById(R.id.course_starting_date);
            place = courseView.findViewById(R.id.course_place);
            title = courseView.findViewById(R.id.course_title);
            courseLinear = courseView.findViewById(R.id.course_cell_layout);
        }
    }

    @NonNull
    @Override
    public CourseViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.course_cell_def, parent, false);
        CourseViewHolder cvh = new CourseViewHolder(view);
        return cvh;
    }

    @Override
    public void onBindViewHolder(@NonNull CourseViewHolder holder, int position) {
        final String title = courseList.get(position).getTitle();
        final String category = courseList.get(position).getCourseCategory().getName();
        final String description = courseList.get(position).getContent();
        final String place = courseList.get(position).getLocation().getName();
        final String startDate = String.valueOf(courseList.get(position).getStartingDate());
        final int availablePlace = courseList.get(position).getAvailablePlace();
        final String teacher = courseList.get(position).getTeacher().getName();
        final String teacherEmail = courseList.get(position).getTeacher().getEmail();
        final String teacherMobile = courseList.get(position).getTeacher().getPhone();
        final String duration = courseList.get(position).getDuration().getName();
        final String level = courseList.get(position).getLevel().getName();
        final String price = String.valueOf(courseList.get(position).getPrice());
        final int image = courseList.get(position).getResImage();

        holder.courseImage.setImageResource(image);
        holder.startingDate.setText(startDate);
        holder.place.setText(place);
        holder.title.setText(title);

        holder.courseLinear.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(v.getContext(), DetailCourseActivity.class);
                intent.putExtra("title", title);
                intent.putExtra("category", category);
                intent.putExtra("content", description);
                intent.putExtra("startDate", startDate);
                intent.putExtra("availablePlace", availablePlace);
                intent.putExtra("teacher", teacher);
                intent.putExtra("teacherEmail", teacherEmail);
                intent.putExtra("teacherMobile", teacherMobile);
                intent.putExtra("duration", duration);
                intent.putExtra("price", price);
                intent.putExtra("place", place);
                intent.putExtra("level", level);
                intent.putExtra("image", image);
                v.getContext().startActivity(intent);
                Toast.makeText(context, "Hai premuto su: " + title, Toast.LENGTH_SHORT).show();
            }
        });

    }

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

    public void courseSetSearchOperation(ArrayList<Course> newList){
        courseList = new ArrayList<>();
        courseList.addAll(newList);
        notifyDataSetChanged();
    }
}

新闻:

public class NewsViewAdapter extends RecyclerView.Adapter<NewsViewAdapter.NewsViewHolder> {

    ArrayList<News> newsList;
    Context context;

    public NewsViewAdapter(ArrayList<News> newsList, Context context) {
        this.newsList = newsList;
        this.context = context;
    }

    public NewsViewAdapter(){}

    public static class NewsViewHolder extends RecyclerView.ViewHolder {
        ImageView newsImage;
        TextView newsTitle, newsContent;
        LinearLayout newsLayout;

        NewsViewHolder(View newView){
            super(newView);
            newsImage = newView.findViewById(R.id.news_image);
            newsTitle = newView.findViewById(R.id.news_title);
            newsContent = newView.findViewById(R.id.news_content);
            newsLayout = newView.findViewById(R.id.news_cell_layout);
        }
    }

    @NonNull
    @Override
    public NewsViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.news_cell_def, parent, false);
        NewsViewHolder nvh = new NewsViewHolder(view);
        return nvh;
    }

    @Override
    public void onBindViewHolder(@NonNull NewsViewHolder holder, int position) {

        final String title = newsList.get(position).getTitle();
        final String content = newsList.get(position).getContent();
        final int image = newsList.get(position).getResImage();


        holder.newsImage.setImageResource(image);
        holder.newsTitle.setText(title);
        holder.newsContent.setText(content);

        holder.newsLayout.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                Intent intent = new Intent(v.getContext(), DetailNewsActivity.class);
                intent.putExtra("title", title);
                intent.putExtra("content", content);
                intent.putExtra("image", image);
                v.getContext().startActivity(intent);
                Toast.makeText(context, "Premuto su: " + title, Toast.LENGTH_SHORT).show();
            }
        });

    }

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

    public void newsSetSearchOperation(ArrayList<News> newList){
        newsList = new ArrayList<>();
        newsList.addAll(newList);
        notifyDataSetChanged();
    }
}

每个特定项目列表都分成一个片段，实际上这里是Main Activity(主页)，我想在其中显示所有主题的RecyclerView:

Each specific list of item is into a fragment, indeed here is the Main Activity (home), where I would like to display a RecyclerView of all the itmes:

public class MainActivity extends AppCompatActivity {

    private DrawerLayout drawerLayout;
    private NavigationView mNavigationView;
    private Toolbar toolbar;
    private ActionBarDrawerToggle drawerToggle;
    private FloatingActionButton fab;
    private RecyclerView mRecyclerView;
    private ImageView openFilter;
    private SearchView searchView;
    private DataMock dataMock = new DataMock();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mRecyclerView = findViewById(R.id.recycler_view_main);
        drawerLayout = findViewById(R.id.drawer_layout);
        mNavigationView = findViewById(R.id.nav_view);
        toolbar = findViewById(R.id.toolbar);
        openFilter = findViewById(R.id.filter_icon);
        searchView = findViewById(R.id.action_search);
        fab = findViewById(R.id.fab);
        fab.show();

        setSupportActionBar(toolbar);
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);

        searchView.setQueryHint(getString(R.string.search_hint));

        drawerToggle = setupDrawerToggle();
        drawerToggle.setDrawerIndicatorEnabled(true);
        drawerToggle.syncState();

        drawerLayout.setDrawerListener(drawerToggle);

        drawerLayout.setDrawerListener(new DrawerLayout.SimpleDrawerListener() {

            @Override
            public void onDrawerOpened(View drawerView) {
                super.onDrawerOpened(drawerView);
            }

            @Override
            public void onDrawerClosed(View drawerView) {
                super.onDrawerClosed(drawerView);
            }
        });

        mNavigationView.setNavigationItemSelectedListener(new NavigationView.OnNavigationItemSelectedListener() {
            @Override
            public boolean onNavigationItemSelected(@NonNull MenuItem menuItem) {
                Fragment nextFragment;
                switch (menuItem.getItemId()){
                    case R.id.event_list:
                        nextFragment = new EventFragment();
                        break;
                    case R.id.course_list:
                        nextFragment = new CourseFragment();
                        break;
                    case R.id.news_list:
                        nextFragment = new NewsFragment();
                        break;
                    default:
                        throw new IllegalArgumentException("No Fragment for the given menu item");
                }
                if (nextFragment != null){
                    getSupportFragmentManager()
                            .beginTransaction()
                            .replace(R.id.anchor_point, nextFragment)
                            .commit();
                    menuItem.setChecked(true);
                    setTitle(menuItem.getTitle());
                    drawerLayout.closeDrawer(mNavigationView);
                }
                return false;
            }
        });

        openFilter.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                BottomSheetDialog filterDialog = new BottomSheetDialog();
                filterDialog.show(getSupportFragmentManager(), "filter dialog opened!");
            }
        });

//        mRecyclerView.setHasFixedSize(true);
//        LinearLayoutManager layoutManager = new LinearLayoutManager(this);
//        mRecyclerView.setLayoutManager(layoutManager);
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // The action bar home/up action should open or close the drawer.
        switch (item.getItemId()) {
            case android.R.id.home:
                drawerLayout.openDrawer(GravityCompat.START);
                return true;
        }

        return super.onOptionsItemSelected(item);
    }

    private ActionBarDrawerToggle setupDrawerToggle() {
        // NOTE: Make sure you pass in a valid toolbar reference.  ActionBarDrawToggle() does not require it
        // and will not render the hamburger icon without it.
        return new ActionBarDrawerToggle(this, drawerLayout, toolbar, R.string.drawer_open,  R.string.drawer_close);
    }

    public void backToHome(View view){

        for (Fragment fragment : getSupportFragmentManager().getFragments()){
            if (fragment != null && (fragment instanceof CourseFragment || fragment instanceof EventFragment || fragment instanceof NewsFragment)){
                getSupportFragmentManager().beginTransaction().remove(fragment).commit();
                toolbar.setTitle("WePress");
                fab.show();
            }
        }
        Toast.makeText(this, "Premuto sul logo", Toast.LENGTH_SHORT).show();
        drawerLayout.closeDrawer(mNavigationView);
    }

    @Override
    protected void onPostCreate(Bundle savedInstanceState) {
        super.onPostCreate(savedInstanceState);
        // Sync the toggle state after onRestoreInstanceState has occurred.
        drawerToggle.syncState();
    }

    @Override
    public void onConfigurationChanged(Configuration newConfig) {
        super.onConfigurationChanged(newConfig);
        // Pass any configuration change to the drawer toggles
        drawerToggle.onConfigurationChanged(newConfig);
    }

    public void addItem(View view){
        PopupMenu popupMenu = new PopupMenu(MainActivity.this, fab);
        popupMenu.getMenuInflater().inflate(R.menu.fab_main_menu, popupMenu.getMenu());
        popupMenu.setOnMenuItemClickListener(new PopupMenu.OnMenuItemClickListener() {
            @Override
            public boolean onMenuItemClick(MenuItem item) {
                switch (item.getItemId()){
                    case R.id.add_event:
                        Toast.makeText(MainActivity.this, "Pronti per aggiungere un evento", Toast.LENGTH_SHORT).show();
                        Intent intentEvent = new Intent(MainActivity.this, AddItemActivity.class);
                        intentEvent.putExtra("isFrom", "event");
                        startActivity(intentEvent);
                        break;
                    case R.id.add_course:
                        Toast.makeText(MainActivity.this, "Pronti per aggiungere un corso", Toast.LENGTH_SHORT).show();
                        Intent intentCourse = new Intent(MainActivity.this, AddItemActivity.class);
                        intentCourse.putExtra("isFrom", "course");
                        startActivity(intentCourse);
                        break;
                    case R.id.add_news:
                        Toast.makeText(MainActivity.this, "Pronti per aggiungere una news", Toast.LENGTH_SHORT).show();
                        Intent intentNews = new Intent(MainActivity.this, AddItemActivity.class);
                        intentNews.putExtra("isFrom", "news");
                        startActivity(intentNews);
                        break;
                }
                return true;
            }
        });
        popupMenu.show();
    }
}

如果可以显示具有不同布局的列表，您还可以提出一种避免重复代码行的方式来提高代码质量的方法吗?如果我没看错，我想重用每个适配器或可以放入特定类(?)的每个适配器. 非常感谢你的帮助！ 如果我缺少一些信息，请问我以编辑帖子.

if it's possible to show the list with differents layouts, can you also suggest a way to improve the quality of my code avoiding to repeat lines of code? If I'm not wrong, I would like to re-use each Adapter or part of them that I can put into a specific class (?). Thank you so much for your help! If I'm missing some information, please ask me in order to edit the post.

推荐答案

您只能对一个视图模型类做一个适配器(使用视图类型) 包含事件，新闻或课程

You must do only one adapter (using view type) with a view model class that contain either an event or a news or a course

适配器应该是这样的:

public class EventViewAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
    private static final int TYPE_EVENT = 10;
    private static final int TYPE_COURSE = 11;
    private static final int TYPE_NEWS = 12;

    ArrayList<EventViewModel> eventList;
    Context context;

    public EventViewAdapter(ArrayList<EventViewModel> eventList, Context context) {
        this.eventList = eventList;
        this.context = context;
    }

    public EventViewAdapter() {
    }

    @Override
    public int getItemViewType(int position) {
        EventViewModel event = eventList.get(position);
        if (event.isEvent()) {
            return TYPE_EVENT ;
        } else if(event.isCourse()) {
            return TYPE_COURSE;
        } else {
            return TYPE_NEWS;
        }
    }

    public static class EventViewHolder extends RecyclerView.ViewHolder {

        ImageView eventImage;
        //....
        EventViewHolder(View eventView) {
            super(eventView);
            eventImage = eventView.findViewById(R.id.event_image);
            //.....
        }
    }

    public static class CourseViewHolder extends RecyclerView.ViewHolder {

        ImageView courseImage;
        //.....

        CourseViewHolder(View courseView) {
        super(courseView);
            courseImage = courseView.findViewById(R.id.course_image);
            //.....
        }

    public static class NewsViewHolder extends RecyclerView.ViewHolder {
        ImageView newsImage;
        //.....

        NewsViewHolder(View newView){
            super(newView);
            newsImage = newView.findViewById(R.id.news_image);
            //.....
        }

    @NonNull
    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {

        if (viewType == TYPE_EVENT) {
            View rootView =     LayoutInflater.from(parent.getContext()).inflate(R.layout.event_cell_def, parent, false);
            return new EventViewHolder (rootView);
        } else if (viewType == TYPE_COURSE) {
            View rootView = LayoutInflater.from(parent.getContext()).inflate(R.layout.course_cell_def, parent, false);
            return new CourseViewHolder(rootView);
        } else {
            View rootView = LayoutInflater.from(parent.getContext()).inflate(R.layout.news_cell_def, parent, false);
            return new NewsViewHolder(rootView);
        }

    }

    @Override
    public void onBindViewHolder(@NonNull EventViewHolder holder, int position) 
    {
        final EventViewModel eventViewModel = eventList.get(position);
        if (eventViewModel .isEvent()) {
            onBindEvent(holder, eventViewModel.getEvent());
        } else if(eventViewModel .isCourse()) {
            onBindCourse(holder, eventViewModel.getCourse());
        } else {
            onBindNews(holder, eventViewModel.getNews());
        }
    }

    private void onBindEvent(RecyclerView.ViewHolder holder, Event event) {
        EventViewHolder eventHolder= (EventViewHolder ) holder;

        final String title = event.getTitle();
        final String description = event.getDescription();
        // others ...

        holder.eventImage.setImageResource(image);
        holder.startingDate.setText(startDate);
        // others ...

        holder.cellLayout.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
            }
        });
        // ...
    }

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

    public void eventSetSearchOperation(ArrayList<Event> newList){
        eventList = new ArrayList<>();
        eventList.addAll(newList);
        notifyDataSetChanged();
    }
}

还有一个类似的View Model类:

And a View Model classes like that :

public class EventViewModel() {

    private Event mEvent;
    private Course mCourse;
    private News mNews;

    private EventViewModel(Event event, Course course, News news) {
        this.mEvent = event;
        this.mCourse = course;
        this.mNews = news;
    }

    public boolean isEvent() {
        return mEvent != null
    }
    public boolean isCourse() {
        return mCourse != null
    }
    public boolean isNews() {
        return mNews != null
    }

    public static EventViewModel getEventInstance(Event event) {
        return new EventViewModel(event, null, null 
    } 
    public static EventViewModel getCourseInstance(Course course) {
        return new EventViewModel(null, course, null 
    } 
    public static EventViewModel getNewsInstance(News news) {
        return new EventViewModel(null, null, news
    } 

    public Event getEvent() {
        return mEvent;
    }
    public Event getCourse() {
        return mScore;
    }
    public Event getNews() {
        return mNews;
    }


}

您可以在所有片段(事件，过程，新闻)中使用此适配器，并且每个片段都会污染EventViewModel列表，并且仅包含其特定类型.主活动中显示的适配器包含用于显示所有事件的所有类型的EventViewModel.

You can use this adapter in all of your fragments (event, course, news) and each fragment contaions a list of EventViewModel with only its specific type. The adapter display in the main activity contains EventViewModel of all types to display all events.

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