@shevyrinn

Как отобразить в RecycleView данные из ArrayList?

Переписываю приложение под использование RecycleView. Пишу по примерам из интернета.
Возникла проблема с отображением в RecycleView данных из ArrayList. В чем проблема? ListView прекрасно работал с ним.
Код RecycleAdapter.java:
spoiler
public class RecyclerAdapter extends RecyclerView.Adapter<RecyclerAdapter.ViewHolder> {

    private List<String> mTitles;

    public RecyclerAdapter(List<String> titles) {
        mTitles = titles;
    }

    public static class ViewHolder extends RecyclerView.ViewHolder {
        public TextView mTextView;

        public ViewHolder(View v) {
            super(v);
            mTextView = (TextView) v.findViewById(R.id.rw_title);
        }
    }

    @Override
    public RecyclerAdapter.ViewHolder onCreateViewHolder(ViewGroup parent,
                                                         int viewType) {
        View v = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.recycler_item, parent, false);

        ViewHolder vh = new ViewHolder(v);
        return vh;
    }

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

        holder.mTextView.setText(mTitles.get(position));

    }

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



Android Monitor
spoiler
06-20 17:43:20.040 2268-2268/? I/zygote64: Late-enabling -Xcheck:jni
06-20 17:43:20.064 2268-2268/? I/zygote64: Reinit property: dalvik.vm.checkjni= false
06-20 17:43:20.086 2268-2268/? D/ActivityThread: ActivityThread,attachApplication
06-20 17:43:20.204 2268-2268/ru.stalkerweb.recycleviewsw D/HwFLClassLoader: get used feature list :/feature/used-list failed!
06-20 17:43:20.204 2268-2268/ru.stalkerweb.recycleviewsw D/HwFLClassLoader: USE_FEATURE_LIST had not init! 
06-20 17:43:20.244 2268-2268/ru.stalkerweb.recycleviewsw E/MemoryLeakMonitorManager: MemoryLeakMonitor.jar is not exist!
06-20 17:43:20.247 2268-2268/ru.stalkerweb.recycleviewsw E/Minikin: Could not get cmap table size!
06-20 17:43:20.283 2268-2268/ru.stalkerweb.recycleviewsw I/HwCust: Constructor found for class android.app.HwCustActivityImpl
06-20 17:43:20.284 2268-2268/ru.stalkerweb.recycleviewsw D/HwCust: Create obj success use class android.app.HwCustActivityImpl
06-20 17:43:20.293 2268-2268/ru.stalkerweb.recycleviewsw V/HwPolicyFactory: : success to get AllImpl object and return....
06-20 17:43:20.299 2268-2268/ru.stalkerweb.recycleviewsw I/HwCust: Constructor found for class android.app.HwCustHwWallpaperManagerImpl
06-20 17:43:20.299 2268-2268/ru.stalkerweb.recycleviewsw D/HwCust: Create obj success use class android.app.HwCustHwWallpaperManagerImpl
06-20 17:43:20.334 2268-2268/ru.stalkerweb.recycleviewsw V/HwWidgetFactory: : successes to get AllImpl object and return....
06-20 17:43:20.338 2268-2268/ru.stalkerweb.recycleviewsw V/ActivityThread: ActivityThread,callActivityOnCreate
06-20 17:43:20.429 2268-2268/? D/HwRTBlurUtils: check blur style for HwPhoneWindow-, themeResId : 0x7f0900a8, context : ru.stalkerweb.recycleviewsw.MainActivity@ef3f5b8, Nhwext : 0, get Blur : disable with , null
06-20 17:43:20.431 2268-2268/? D/HwRTBlurUtils: check blur style for HwPhoneWindow-, themeResId : 0x7f0900a8, context : ru.stalkerweb.recycleviewsw.MainActivity@ef3f5b8, Nhwext : 0, get Blur : disable with , null
06-20 17:43:20.486 2268-2268/? D/CubicBezierInterpolator: CubicBezierInterpolator  mControlPoint1x = 0.23, mControlPoint1y = 0.06, mControlPoint2x = 0.09, mControlPoint2y = 0.97
06-20 17:43:20.487 2268-2268/? D/CubicBezierInterpolator: CubicBezierInterpolator  mControlPoint1x = 0.6, mControlPoint1y = 0.9, mControlPoint2x = 0.8, mControlPoint2y = 1.0
06-20 17:43:20.489 2268-2268/? D/CubicBezierInterpolator: CubicBezierInterpolator  mControlPoint1x = 0.23, mControlPoint1y = 0.06, mControlPoint2x = 0.09, mControlPoint2y = 0.97
06-20 17:43:20.490 2268-2268/? D/CubicBezierInterpolator: CubicBezierInterpolator  mControlPoint1x = 0.6, mControlPoint1y = 0.9, mControlPoint2x = 0.8, mControlPoint2y = 1.0
06-20 17:43:20.512 2268-2268/? W/Utils: Utils_isSuperResolutionSupport [load libai_client.so failed]
06-20 17:43:20.526 2268-2268/? D/AndroidRuntime: Shutting down VM
06-20 17:43:20.530 2268-2268/? E/AndroidRuntime: FATAL EXCEPTION: main
                                                 Process: ru.stalkerweb.recycleviewsw, PID: 2268
                                                 java.lang.RuntimeException: Unable to start activity ComponentInfo{ru.stalkerweb.recycleviewsw/ru.stalkerweb.recycleviewsw.MainActivity}: java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference
                                                     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3194)
                                                     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3302)
                                                     at android.app.ActivityThread.-wrap12(Unknown Source:0)
                                                     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1891)
                                                     at android.os.Handler.dispatchMessage(Handler.java:108)
                                                     at android.os.Looper.loop(Looper.java:166)
                                                     at android.app.ActivityThread.main(ActivityThread.java:7425)
                                                     at java.lang.reflect.Method.invoke(Native Method)
                                                     at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:245)
                                                     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:921)
                                                  Caused by: java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference
                                                     at ru.stalkerweb.recycleviewsw.MainActivity.onCreate(MainActivity.java:51)
                                                     at android.app.Activity.performCreate(Activity.java:7372)
                                                     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1218)
                                                     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3147)
                                                     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3302) 
                                                     at android.app.ActivityThread.-wrap12(Unknown Source:0) 
                                                     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1891) 
                                                     at android.os.Handler.dispatchMessage(Handler.java:108) 
                                                     at android.os.Looper.loop(Looper.java:166) 
                                                     at android.app.ActivityThread.main(ActivityThread.java:7425) 
                                                     at java.lang.reflect.Method.invoke(Native Method) 
                                                     at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:245) 
                                                     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:921) 
06-20 17:43:20.543 2268-2268/? I/Process: Sending signal. PID: 2268 SIG: 9

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Решения вопроса 1
zagayevskiy
@zagayevskiy Куратор тега Java
Android developer at Yandex
Ты создаёшь адаптер до того, как создал titles(Т.е., когда в этой переменной null). Всё, что происходит с этой переменной после создания адаптера неважно, тк ссылка внутри уже null.

Для упрощения отлова таких ситуаций рекомендую использовать аннотации @NonNull / @Nullable везде, где это возможно. Также можено настроить IDE так, что любое поле, не помеченное @NonNull считается @Nullable.
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Ответы на вопрос 1
@shevyrinn Автор вопроса
MainActivity.java
spoiler
public class MainActivity extends AppCompatActivity {

    URL url;
    List<String> titles;
    ArrayList<String> links;
    ArrayList<String> description;
    ArrayList<String> pubDate;
    ArrayList<String> author;
    ArrayList<String> category;
    String HHMurl= "https://stalkerweb.ru/feed";


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        RecyclerView mRecyclerView = (RecyclerView) findViewById(R.id.my_recycler_view);

        mRecyclerView.setHasFixedSize(false);

        RecyclerView.LayoutManager mLayoutManager = new LinearLayoutManager(this);
        mRecyclerView.setLayoutManager(mLayoutManager);
   
        RecyclerView.Adapter mAdapter = new RecyclerAdapter(titles);
        mRecyclerView.setAdapter(mAdapter);
        try{
        titles = new ArrayList<>();
        links = new ArrayList<>();
        description = new ArrayList<>();
        pubDate = new ArrayList<>();
        author = new ArrayList<>();
        category = new ArrayList<>();

        RecycleClick.addTo(mRecyclerView).setOnItemClickListener(new RecycleClick.OnItemClickListener() {
            @Override
            public void onItemClicked(RecyclerView recyclerView, int position, View v) {

                 //to do something

            }

        });
            new ProcessInBackground().execute();

        } catch(Exception e){
            //to do something
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        int id = item.getItemId();

        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }


    public InputStream getInputStream (URL url)
    {
        try {
            return url.openConnection().getInputStream();
        } catch (IOException e) {
            return null;
        }
    }

    private class ProcessInBackground extends AsyncTask<Integer, Void, Exception> {

        ProgressDialog progressDialog = new ProgressDialog(MainActivity.this);

        Exception exception = null;

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            progressDialog.setMessage("Загрузка...");
            progressDialog.show();
        }

        @Override
        protected Exception doInBackground(Integer... params) {

            try {
                url = new URL(HHMurl);
                XmlPullParserFactory factory = XmlPullParserFactory.newInstance();
                factory.setNamespaceAware(false);
                XmlPullParser xpp = factory.newPullParser();
                xpp.setInput(getInputStream(url), "UTF_8");
                boolean insideItem = false;
                int eventType = xpp.getEventType();

                while (eventType != XmlPullParser.END_DOCUMENT) {
                    if (eventType == XmlPullParser.START_TAG) {
                        if (xpp.getName().equalsIgnoreCase("item")) {
                            insideItem = true;
                        } else if (xpp.getName().equalsIgnoreCase("title")) {
                            if (insideItem) {
                                titles.add(xpp.nextText());
                            }
                        } else if (xpp.getName().equalsIgnoreCase("link")) {
                            if (insideItem) {
                                links.add(xpp.nextText());
                            }
                        } else if (xpp.getName().equalsIgnoreCase("content:encoded")) {
                            if (insideItem) {
                                description.add(xpp.nextText());
                            }
                        } else if (xpp.getName().equalsIgnoreCase("pubDate")) {
                            if (insideItem) {
                                pubDate.add(xpp.nextText());
                            }
                        } else if (xpp.getName().equalsIgnoreCase("dc:creator")) {
                            if (insideItem) {
                                author.add(xpp.nextText());
                            }
                        } else if (xpp.getName().equalsIgnoreCase("category")) {
                            if (insideItem) {
                                category.add(xpp.nextText());
                            }
                        }

                    } else if (eventType == XmlPullParser.END_TAG && xpp.getName().equalsIgnoreCase("item")) {
                        insideItem = false;
                    }

                    eventType = xpp.next();
                }


            } catch (XmlPullParserException | IOException e) {
                exception = e;
            }

            return exception;
        }

    }}

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