ViewPager 片段都引用相同的 RecyclerView and/or 适配器

Question

我有一个包含 RecyclerView 的 Fragment 来显示给定日期的事件。我正在使用 ViewPager 将片段分成多天；周六活动的片段和周日活动的片段。

但是，两个片段似乎都引用了同一个 RecyclerView and/or 适配器，因为它只是显示事件的最后一个选项卡（在本例中为星期日）。

在我的具体情况下，周六有两个事件，周日没有事件。两个片段都有空的 RecyclerView。为了证实我的理论，它是由最后一个标签引起的，我切换了日期。这导致两个 RecyclerView 都有两个事件（星期六的事件）。

这里是各个片段的相关代码：

public class EventListFragment extends Fragment{
    private EventAdapter mEventAdapter;

    private static final String DATE_ARG = "eventDate";

    public static EventListFragment newInstance(LocalDate date){
        EventListFragment eventListFragment = new EventListFragment();
        Bundle args = new Bundle();
        args.putSerializable(DATE_ARG, date);
        eventListFragment.setArguments(args);
        return eventListFragment;
    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_event_list, container, false);

        // Setup recyclerview
        RecyclerView eventRecyclerView = (RecyclerView) view.findViewById(R.id.event_recycler_view);
        LinearLayoutManager layoutManager = new LinearLayoutManager(getActivity());
        layoutManager.setOrientation(LinearLayoutManager.VERTICAL);
        eventRecyclerView.setLayoutManager(layoutManager);

        // Get date
        LocalDate eventDate = (LocalDate) getArguments().getSerializable(DATE_ARG);

        // Set adapter
        mEventAdapter = new EventAdapter(getActivity(), getEvents(eventDate));
        eventRecyclerView.setAdapter(mEventAdapter);

        return view;
    }
}

getEvents() 只是给定日期的 return 事件的私有函数。我已经使用调试器和单元测试来验证它是否正常工作。调试器显示它为每个片段提取了正确的列表，但正如我所解释的那样，它们显示不正确。

父片段的相关代码如下：

public class EventFragment extends Fragment {
    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_event, container, false);

        // Get and set up viewpager
        final ViewPager viewPager = (ViewPager) view.findViewById(R.id.event_view_pager);
        EventFragmentAdapter eventFragmentAdapter = new EventFragmentAdapter(getFragmentManager(), getEventDates());
        viewPager.setAdapter(eventFragmentAdapter);

        // Get and set up tablayout
        final TabLayout tabLayout = (TabLayout) view.findViewById(R.id.event_tabs);
        tabLayout.setTabGravity(TabLayout.GRAVITY_FILL);

        tabLayout.post(new Runnable() {
            @Override
            public void run() {
                tabLayout.setupWithViewPager(viewPager);
            }
        });

        return view;
    }
}

与上一个类似，getEventDates() 只是提取事件发生的日期。目前出于测试目的，我正在硬编码 returned 日期列表，因为我们还没有设置数据库。我取消了这个方法，因为我希望应用程序能够在 2016 年再次运行，这可能有不同的日期：

private List<LocalDate> getEventDates(){
    List<LocalDate> eventDates = new ArrayList<>();

    eventDates.add(new LocalDate(2015, 10, 17));
    eventDates.add(new LocalDate(2015, 10, 18));

    return eventDates;
}

最后一点相关代码是针对我用于 ViewPager 的 FragmentStatePagerAdapter 的：

public class EventFragmentAdapter extends FragmentStatePagerAdapter {
    private List<LocalDate> mEventDates;

    public EventFragmentAdapter(FragmentManager fragmentManager, List<LocalDate> eventDates){
        super(fragmentManager);
        this.mEventDates = eventDates;
    }
    @Override
    public Fragment getItem(int i) {
        return EventListFragment.newInstance(mEventDates.get(i));
    }

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

    @Override
    public CharSequence getPageTitle(int position) {
        return mEventDates.get(position).dayOfWeek().getAsText();
    }
}

知道为什么两个列表总是相同的，并且基于 ViewPager 中的最后一个选项卡吗？我假设它们以某种方式引用相同的 RecyclerView 或相同的 RecyclerViewAdapter，但我没有任何静态字段，所以我不确定它是如何发生的。

Answer 1

你能试试这个吗？

public class EventFragmentAdapter extends FragmentStatePagerAdapter {
    private List<LocalDate> mEventDates;
    private List<EventListFragment> mFragments;


    public EventFragmentAdapter(FragmentManager fragmentManager, List<LocalDate> eventDates){
        super(fragmentManager);
        this.mEventDates = eventDates;
        this.mFragments = new ArrayList<>;
        for (LocalDate date : this.mEventDates) {
            this.mFragments.add(EventListFragment.newInstance(date));
        }
    }

    @Override
    public Fragment getItem(int i) {
        return mFragments.get(i);
    }

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

    @Override
    public CharSequence getPageTitle(int position) {
        return mEventDates.get(position).dayOfWeek().getAsText();
    }
}

然后检查mFragents的每一项是否有预期的内容。

Answer 2

漫长的寻找和反高潮的解决方案（与最困难的错误一样）。也有点不公平，因为错误不在上面发布的代码中，我不得不寻找你的 git 项目来解决它。该错误位于 EventAdapter:

public class EventAdapter extends RecyclerView.Adapter<EventAdapter.ViewHolder> {
    private static final List<Event> mEvents;
    private final Context mContext;

    public EventAdapter(Context context, List<Event> events){
        this.mContext = context;
        mEvents = events;
    }
    ...
}

mEvents 是静态的！...所以它在 mEvents 的所有实例之间共享。这完美地解释了这个错误，因为最后更新它会设置所有 EventAdapters.

的值

您似乎将 mEvents 设为静态，以便您可以在 ViewHolders 中访问它。相反，您可以只将单个事件存储在 ViewHolder 中并删除 dangerous static 修饰符。另一方面，开源项目万岁！

Answer 3

我看过你的代码，我完全同意 Travor 的观点——你使用的是静态成员，每次你创建新的适配器时都会替换它（因此它只获取最后一页数据）。我对您的项目做了一些修改，以使其正常工作。看看吧，希望对你有用

EventFragment：将 getFragmentManager 替换为 getChildFragmentManager，因为您需要 EventListFragment 由 EventFragment 片段管理器处理，而不是由 activity 片段管理器

public class EventFragment extends Fragment {

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_event, container, false);

        // Get and set up viewpager
        final ViewPager viewPager = (ViewPager) view.findViewById(R.id.event_view_pager);
        EventFragmentAdapter eventFragmentAdapter = new EventFragmentAdapter(getChildFragmentManager(), getEventDates());
        viewPager.setAdapter(eventFragmentAdapter);

        // Get and set up tablayout
        final TabLayout tabLayout = (TabLayout) view.findViewById(R.id.event_tabs);
        tabLayout.setTabGravity(TabLayout.GRAVITY_FILL);

        tabLayout.post(new Runnable() {
            @Override
            public void run() {
                tabLayout.setupWithViewPager(viewPager);
            }
        });

        return view;
    }

    /**
     * Retrieves the event dates for the hackathon so that the proper events can be displayed.
     * @return
     */
    private List<LocalDate> getEventDates(){
        List<LocalDate> eventDates = new ArrayList<>();

        eventDates.add(new LocalDate(2015, 10, 17));
        eventDates.add(new LocalDate(2015, 10, 18));

        return eventDates;
    }
}

EventListFragment - 我修改了查询，因为 sqlite 查询不适用于我的语言环境（意大利语）

public class EventListFragment extends Fragment{

    private EventAdapter mEventAdapter;

    private static final String TAG = EventListFragment.class.getSimpleName();

    private static final String DATE_ARG = "eventDate";

    public static EventListFragment newInstance(LocalDate date){
        EventListFragment eventListFragment = new EventListFragment();
        Bundle args = new Bundle();
        args.putSerializable(DATE_ARG, date);
        eventListFragment.setArguments(args);
        return eventListFragment;
    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_event_list, container, false);

        // Setup recyclerview
        RecyclerView eventRecyclerView = (RecyclerView) view.findViewById(R.id.event_recycler_view);
        LinearLayoutManager layoutManager = new LinearLayoutManager(getActivity());
        layoutManager.setOrientation(LinearLayoutManager.VERTICAL);
        eventRecyclerView.setLayoutManager(layoutManager);

        // Get date
        LocalDate eventDate = (LocalDate) getArguments().getSerializable(DATE_ARG);

        // Set adapter
        mEventAdapter = new EventAdapter(getEvents(eventDate));
        eventRecyclerView.setAdapter(mEventAdapter);

        Log.v(TAG, eventRecyclerView.toString());

        return view;
    }

    /**
     * Retrieves the events for the given date for the fragment.
     */
    private List<Event> getEvents(LocalDate date){
        List<Event> returnList = new ArrayList<>();

        String dateString = Utility.getDBDateString(date);
        List<String> dateList = new ArrayList<>();

        Cursor cursor = getActivity().getContentResolver().query(
                GHContract.EventEntry.CONTENT_URI,
                new String[]{ "*", "substr(" + GHContract.EventEntry.COLUMN_TIME + ",0,11)" },
                "substr(" + GHContract.EventEntry.COLUMN_TIME + ",0,11) = ? ",
                new String[]{dateString},
                GHContract.EventEntry.COLUMN_TIME
        );

        while(cursor.moveToNext()){
            returnList.add(new Event(cursor));
            dateList.add(cursor.getString(cursor.getColumnIndex(GHContract.EventEntry.COLUMN_TIME)));
        }

        cursor.close();

        return returnList;
    }
}

EventAdapter - 删除了静态关键字和对 activity 上下文的引用（您需要在其他地方获取上下文）

public class EventAdapter extends RecyclerView.Adapter<EventAdapter.ViewHolder> {
    private List<Event> mEvents;

    public EventAdapter(List<Event> events){
        mEvents = events;
    }

    /**
     * Inflates the view for Event items.
     */
    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.list_item_event, parent, false);
        return new ViewHolder(view);
    }

    /**
     * Binds the data for an event to its view.
     */
    @Override
    public void onBindViewHolder(ViewHolder holder, int position) {
        Event event = mEvents.get(position);
        holder.timeView.setText(Utility.getTimeString(event.getTime()));
        holder.titleView.setText(event.getTitle());
        holder.locationView.setText(event.getLocation());

        // If reminder time is not null, show check mark. If it is, show plus.
        if(event.getReminderTime() != null){
            holder.alarmView.setImageDrawable(holder.itemView.getResources().getDrawable(R.drawable.ic_alarm_on));
        } else{
            holder.alarmView.setImageDrawable(holder.itemView.getResources().getDrawable(R.drawable.ic_add_alarm));
        }
    }

    /**
     * Returns the size of the adapter.
     */
    @Override
    public int getItemCount() {
        return mEvents.size();
    }

    /**
     * Retains a reference to the view so `findViewById` calls are only made once for the adapter.
     */
    public class ViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener{
        public final TextView timeView;
        public final TextView titleView;
        public final TextView locationView;
        public final ImageView alarmView;

        public ViewHolder(View view){
            super(view);
            timeView = (TextView) view.findViewById(R.id.event_time);
            titleView = (TextView) view.findViewById(R.id.event_title);
            locationView = (TextView) view.findViewById(R.id.event_location);
            alarmView = (ImageView) view.findViewById(R.id.event_add_reminder);
            alarmView.setOnClickListener(this);
        }

        /**
         * Handles the click a user makes on the alarm image view.
         */
        @Override
        public void onClick(View v) {
            OnEventReminderClickListener activity = (OnEventReminderClickListener) v.getContext();
            activity.onEventReminderClicked(mEvents.get(getPosition()));
        }
    }

    /**
     * Interface to call back to the activity when an alarm is clicked for an event item.
     */
    public interface OnEventReminderClickListener{
        void onEventReminderClicked(Event event);
    }
}

最后是 app/build.gradle，因为您需要为所有支持库（回收器、卡片等）获取相同的版本

apply plugin: 'com.android.application'

android {
    compileSdkVersion 22
    buildToolsVersion "22.0.1"

    defaultConfig {
        applicationId "com.adammcneilly.grizzhacks"
        minSdkVersion 15
        targetSdkVersion 22
        versionCode 1
        versionName "1.0"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    compile 'com.android.support:appcompat-v7:22.2.1'
    compile 'joda-time:joda-time:2.7'
    compile 'com.android.support:recyclerview-v7:22.2.1'
    compile 'com.android.support:cardview-v7:22.2.1'
    compile 'com.android.support:design:22.2.1'
}

ViewPager 片段都引用相同的 RecyclerView and/or 适配器

ViewPager fragments are all referencing the same RecyclerView and/or Adapter

android

android-fragments

android-viewpager

android-recyclerview