CODEWITHSUNDEEP
androidandroid-recyclerview
user2009490
user2009490

Reputation: 348

Android. RecyclerView. Error class inheritance: ...on a null object reference

There is a basic class. I threw too much for the sake of brevity. At the start of this activity all works.

public class MainActivity extends DrawerActivity {
    protected Activity activity = this;
    protected class GetDataFromMongoDb extends AsyncTask<String, Integer, ArrayList<CurrentNewsItem>> {
        protected ArrayList<CurrentNewsItem> doInBackground(String... provider) {
            //put data in array for adapter
        }
        protected void onPostExecute(final ArrayList<CurrentNewsItem> result) {
            adapter = new RecyclerAdapter(result);
            StaggeredGridLayoutManager llm = new StaggeredGridLayoutManager(UtilsScreen.getDisplayColumns((Activity) activity), StaggeredGridLayoutManager.VERTICAL);
            rv.setLayoutManager(llm);
            rv.setAdapter(adapter);
        }
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        LayoutInflater inflater = (LayoutInflater) this.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        View contentView = inflater.inflate(R.layout.activity_main, null, false);
        mDrawer.addView(contentView, 0);

        CurrentSection = ("news");
        rv = (RecyclerView)findViewById(R.id.rv_main);
        new GetDataFromMongoDb().execute(CurrentSection);
    }
}

extended

public class News extends MainActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        LayoutInflater inflater = (LayoutInflater) this.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        View contentView = inflater.inflate(R.layout.activity_news, null, false);
        mDrawer.addView(contentView, 0);

        CurrentSection = getIntent().getExtras().getString("section");
        rv = (RecyclerView)findViewById(R.id.rv);
        new GetDataFromMongoDb().execute(CurrentSection);
    }
}

When you go to News screen is blank, Clicking get the error:

E/InputEventReceiver﹕ Exception dispatching input event. E/MessageQueue-JNI﹕ Exception in MessageQueue callback: handleReceiveCallback E/MessageQueue-JNI﹕ java.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.support.v7.widget.RecyclerView$LayoutManager.canScrollVertically()' on a null object reference

Where am I wrong?

Upvotes: 3

Views: 2106

Answers (1)

Vilen
Vilen

Reputation: 5061

you must supply layout manager to your recylcerview add following just after

rv = (RecyclerView)findViewById(R.id.rv);

and it will not crash

LinearLayoutManager layoutManager = new LinearLayoutManager(context);
layoutManager.setOrientation(LinearLayoutManager.VERTICAL);
rv.setLayoutManager(layoutManager);

Upvotes: 2

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