NullPointerException in onItemClick()

Question

I am creating navigation drawer list view that make changes in a specific text view according to the position of the list view , but always had that exception many times and I don't know how to solve it

MainActivity Class

public class DBHelper extends SQLiteOpenHelper {

     private static String DB_NAME = "duaa.sqlite";
     private SQLiteDatabase db;
     private final Context context;
     private String DB_PATH;

     public DBHelper(Context context) {
      super(context, DB_NAME, null, 1);
      this.context = context;
      DB_PATH = "/data/data/" + context.getPackageName() + "/" + "databases/";
     }

     public void createDataBase() throws IOException {

      boolean dbExist = checkDataBase();
      if (dbExist) {

      } else {
       this.getReadableDatabase();
       try {
        copyDataBase();
       } catch (IOException e) {
        throw new Error("Error copying database");
       }
      }
     }

     private boolean checkDataBase() {
      File dbFile = new File(DB_PATH + DB_NAME);
      return dbFile.exists();
     }

     private void copyDataBase() throws IOException {

      InputStream myInput = context.getAssets().open(DB_NAME);
      String outFileName = DB_PATH + DB_NAME;
      OutputStream myOutput = new FileOutputStream(outFileName);
      byte[] buffer = new byte[1024];
      int length;
      while ((length = myInput.read(buffer)) > 0) {
       myOutput.write(buffer, 0, length);
      }

      // Close the streams
      myOutput.flush();
      myOutput.close();
      myInput.close();

     }

     public Cursor getData() {
      String myPath = DB_PATH + DB_NAME;
      db = SQLiteDatabase.openDatabase(myPath, null,
        SQLiteDatabase.OPEN_READONLY);
      Cursor c = db.query("main", null, null, null, null,null,null);
       // Note: Master is the one table in External db. Here we trying to access the records of table from external db.
      return c;
     }

     @Override
     public void onCreate(SQLiteDatabase arg0) {
      // TODO Auto-generated method stub
     }

     @Override
     public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
      // TODO Auto-generated method stub
     }
}

DbHelper Class that extends SQLiteOpenHelper

public class MainActivity extends ActionBarActivity {

        ListView lv;
        DrawerList adapter;
        DrawerLayout drawer;
        String[] duaaList;
        ActionBarDrawerToggle drawerToggle;
        TextView tv;
        ArrayList<String>data;
        DBHelper helper;




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

            duaaList = getResources().getStringArray(R.array.duaa);

            drawer = (DrawerLayout) findViewById(R.id.drawer_layout);

            tv = (TextView) findViewById(R.id.tvDesc);

            lv = (ListView) findViewById(R.id.left_drawer);

            adapter = new DrawerList();

            lv.setAdapter(adapter);



            drawerToggle = new  ActionBarDrawerToggle(this,drawer,0,0);

            lv.setOnItemClickListener(new AdapterView.OnItemClickListener() {


                @Override
                public void onItemClick(AdapterView<?> parent, View view, int position, long id) {

                    selectItem(position);

                    changeText(position);


                }
                public void selectItem(int position){
                    lv.setItemChecked(position, true);
                    setTitle(duaaList[position]);
                }
                public void setTitle(String title){
                    getSupportActionBar().setTitle(title);
                }

              //set data into a textview according to the position of the list 
                public void changeText(int position){
                try{    

                    lv.setItemChecked(position, true);
                    lv.setSelection(position);
                    drawer.closeDrawer(lv);

                    tv.setText(data.get(position));       
                }catch(Exception e){
                    e.printStackTrace();
                }
             }

            });

    }





        public void changeTextView(){
            helper = new DBHelper(getBaseContext());
            try {
                helper.createDataBase();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

            Cursor c = helper.getData();
          if(c.moveToFirst() && c != null)
          {
            do {
                data.add(c.getString(c.getColumnIndex("desc")));
            } while (c.moveToNext());   
          } 
        }



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

        @Override
        public boolean onOptionsItemSelected(MenuItem item) {

            int id = item.getItemId();

            if (id == R.id.action_settings) {
                finish();
            }

            return super.onOptionsItemSelected(item);
        }

        class DrawerList extends BaseAdapter{


            @Override
            public int getCount() {
                return duaaList.length;
            }

            @Override
            public Object getItem(int position) {
                return duaaList[position];
            }

            @Override
            public long getItemId(int position) {
                return position;
            }

            @Override
            public View getView(int position, View convertView, ViewGroup parent) {
                View v = convertView;
                if (v == null){
                    v = getLayoutInflater().inflate(R.layout.duaa_list_item , parent , false);
                }
                TextView tv = (TextView) v.findViewById(R.id.tv2);
                tv.setText(duaaList[position]);

                return v;
            }
        }

    }

and here the xml file

 <android.support.v4.widget.DrawerLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        android:id="@+id/drawer_layout"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
        <!-- The main content view -->

        <FrameLayout
            android:id="@+id/content_frame"
            android:layout_width="match_parent"
            android:layout_height="match_parent" >

    <ScrollView
        android:layout_width="match_parent"
        android:layout_height="480dp" >

            <LinearLayout
                android:layout_width="fill_parent"
                android:layout_height="fill_parent"
                android:orientation="vertical" >

                <TextView
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:textAppearance="?android:attr/textAppearanceMedium"
                    android:text="Medium Text"
                    android:id="@+id/tvDesc"
                    android:layout_gravity="center"
                    android:paddingTop="10dp"
                    />
            </LinearLayout>

    </ScrollView>
        </FrameLayout>
        <!-- The navigation drawer -->
        <ListView android:id="@+id/left_drawer"
            android:layout_width="290dp"
            android:layout_height="match_parent"
            android:layout_gravity="start"
            android:choiceMode="singleChoice"
            android:splitMotionEvents="true"
            android:soundEffectsEnabled="true"
            android:divider="@android:color/darker_gray"
            android:dividerHeight="1dp"
            android:background="#ffbababa"/>

    </android.support.v4.widget.DrawerLayout>

Here is the exception:

04-13 14:26:00.573: W/System.err(18010): java.lang.NullPointerException 04-13 14:26:00.573: W/System.err(18010): at com.anabil.duaaapp.MainActivity$1.changeText(MainActivity.java:98) 04-13 14:26:00.573: W/System.err(18010): at com.anabil.duaaapp.MainActivity$1.onItemClick(MainActivity.java:78) 04-13 14:26:00.573: W/System.err(18010): at android.widget.AdapterView.performItemClick(AdapterView.java:299) 04-13 14:26:00.573: W/System.err(18010): at android.widget.AbsListView.performItemClick(AbsListView.java:1113) 04-13 14:26:00.573: W/System.err(18010): at android.widget.AbsListView$PerformClick.run(AbsListView.java:2911) 04-13 14:26:00.573: W/System.err(18010): at android.widget.AbsListView$3.run(AbsListView.java:3645) 04-13 14:26:00.573: W/System.err(18010): at android.os.Handler.handleCallback(Handler.java:733) 04-13 14:26:00.573: W/System.err(18010): at android.os.Handler.dispatchMessage(Handler.java:95) 04-13 14:26:00.573: W/System.err(18010): at android.os.Looper.loop(Looper.java:136) 04-13 14:26:00.573: W/System.err(18010): at android.app.ActivityThread.main(ActivityThread.java:5001) 04-13 14:26:00.573: W/System.err(18010): at java.lang.reflect.Method.invokeNative(Native Method) 04-13 14:26:00.573: W/System.err(18010): at java.lang.reflect.Method.invoke(Method.java:515) 04-13 14:26:00.573: W/System.err(18010): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785) 04-13 14:26:00.573: W/System.err(18010): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601) 04-13 14:26:00.573: W/System.err(18010): at dalvik.system.NativeStart.main(Native Method)

score 0 · Answer 1 · answered Apr 13 '15 at 19:08

I don't see where you initialise your ArrayList<String> data, I only see you trying to add some stuff in it in your importDB(). I doubt you were able to see this log at all: Log.d("TAG" , "the database has been successfully readed :)" );. The line that causes the NullPointerException is most likely this one: tv.setText(data.get(position));

Anyways, couple of notes:

In the code you pasted you're trying to handle the DB import in your UI thread (because you're calling readOrCopyFile() directly from onCreate()). That's a really bad idea, as your app can get unresponsive for a good amount of time. At least extract this to an AsyncTask.
The log says your NullPointerException happens in changeText(). Assuming you've initialised the data array somewhere, to avoid further problems you should totally check it's size() before calling data.get(position) on it.

i have updated the post , but still the same error , i think this way easy to understand ? — Ahmed Nabil, Apr 14 '15 at 06:27

NullPointerException in onItemClick()

1 Answers1