Android: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Object.toString()' on a null object reference

Question

Facing a problem with a practice app I'm working on. I'm facing a NullPointerException problem relating to the toString method. Being new to android app development, I'm unsure of the exact cause even after my research into this. Hence I ask for someone who is more familiar with the stack trace to kindly help me out.

Note: The error occurs when I click on the listview entry to access an edit page for the diary entry. However it doesn't seem to go to the edit page at all.

Below you'll find my activity code it occurs on and the stack trace.

Activity code:

import android.app.AlertDialog;
import android.content.DialogInterface;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;

import android.content.Intent;

import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;

import java.util.ArrayList;


public class ViewDiaryEntries extends AppCompatActivity {

// Database Helper
MyDBHandler db;

// Listview
ListView data_list;

// Test var
public final static String KEY_EXTRA_DATA_ID = "KEY_EXTRA_DATA_ID";

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

    db = new MyDBHandler(this);

    // Displays the database items.
    displayItems();
}

// To display items in the listview.
public void displayItems(){
    // To display items in a listview.
    ArrayList db_data_list = db.getDiaryDBDataList();
    ArrayAdapter listAdapter = new ArrayAdapter(this, android.R.layout.simple_list_item_1, db_data_list);

    // Set the adapter for the listview
    data_list = (ListView) findViewById(R.id.dataListView);
    data_list.setAdapter(listAdapter);

    /* Experiment -------------------------------------------------------------*/

    data_list.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
            // Selected item store
            String selectedEntry = ((TextView) view).getText().toString();

            // Test for regular expression
            String[] listViewItemSplit = selectedEntry.split(" - ");
            String listViewItempt1 = listViewItemSplit[0]; // For date and time
            //String listViewItempt2 = listViewItemSplit[1]; // For save file name

            //Toast.makeText(ViewDiaryEntries.this, listViewItempt1, Toast.LENGTH_LONG).show();

            if(listViewItempt1.equals("")){
                Toast.makeText(ViewDiaryEntries.this, "Error. Unable to detect entry ID.", Toast.LENGTH_LONG).show();
            }
            else{
                // Pass on the data:
                Intent editEntry = new Intent(ViewDiaryEntries.this, editdiaryentry.class);
                editEntry.putExtra(KEY_EXTRA_DATA_ID, listViewItempt1);
                startActivity(editEntry);
            }
        }
    });
}

// For the go back button.
public void viewdiarytoinitialdiary_backbutt(View v){
    // Create and start new intent going back ot main page.
    Intent main_page = new Intent(ViewDiaryEntries.this, User_Main_Menu_Options.class);
    main_page.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
    startActivity(main_page);
}

// For the about button.
public void viewdiarypage_directionabout_butt(View v){
    // Create an alert dialog
    final AlertDialog.Builder about_page_dialog = new AlertDialog.Builder(ViewDiaryEntries.this);
    about_page_dialog.setTitle("About This Page:");

    // Inputs values for the dialog message.
    final String dialog_message = "This page will show you any saved diary entries you've.\n\n To edit an entry, do the following: \n\n- Take note of the Entry ID# (first value on entry display) \n- Type it in the number box at the bottom. \n- Press Edit Record icon next to number box, and wait for it to load.";

    about_page_dialog.setMessage(dialog_message);

    about_page_dialog.setPositiveButton("Got it!", new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialog, int which) {
            // Closes the dialog.
            dialog.cancel();
        }
    });

    // Shows the dialog.
    about_page_dialog.show();
}

// Main menu button.
public void viewDiaryEntriesMainMenushortcut_butt(View v){
    // Creates main menu alert dialog.
    AlertDialog.Builder mainMenu_Dialog = new AlertDialog.Builder(this);
    mainMenu_Dialog.setIcon(R.drawable.main_menu_symbol);
    mainMenu_Dialog.setTitle("Main Menu");

    // Creates array adapter with items to fill the menu with.
    final ArrayAdapter<String> menuItemsAdapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1);
    menuItemsAdapter.add("Home Screen");
    menuItemsAdapter.add("Diary");
    menuItemsAdapter.add("Tests");
    menuItemsAdapter.add("Activity");
    menuItemsAdapter.add("Media");
    menuItemsAdapter.add("Thought of the Day");
    menuItemsAdapter.add("Inspirational Quotes");
    menuItemsAdapter.add("Resources");
    menuItemsAdapter.add("Settings");

    // To close menu.
    mainMenu_Dialog.setPositiveButton("Cancel", new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialog, int which) {
            dialog.cancel();
        }
    });

    // To go to appropriate page upon selection.
    mainMenu_Dialog.setAdapter(menuItemsAdapter, new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialog, int which) {
            String selectedItem = menuItemsAdapter.getItem(which);

            if(selectedItem.equals("Home Screen")){
                // Goes to main menu.
                Intent mainMenu = new Intent(ViewDiaryEntries.this, User_Main_Menu_Options.class);
                mainMenu.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
                startActivity(mainMenu);
            }
            else if(selectedItem.equals("Diary")){
                // Goes to diary page.
                Intent diaryPage = new Intent(ViewDiaryEntries.this, ViewDiaryEntries.class);
                diaryPage.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
                startActivity(diaryPage);
            }
            else if(selectedItem.equals("Tests")){
                // Goes to tests page.
                Intent testsPage = new Intent(ViewDiaryEntries.this, TestChoices.class);
                testsPage.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
                startActivity(testsPage);
            }
            else if(selectedItem.equals("Media")){
                // Goes to media page.
                Intent mediaPage = new Intent(ViewDiaryEntries.this, initialMediaPage.class);
                mediaPage.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
                startActivity(mediaPage);
            }
            else if(selectedItem.equals("Thought of the Day")){
                // Goes to thought of the day page.
                Intent thoughtofthedayPage = new Intent(ViewDiaryEntries.this, thoughtQuotes.class);
                thoughtofthedayPage.putExtra("quote_or_thought", 2);
                thoughtofthedayPage.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
                startActivity(thoughtofthedayPage);
            }
            else if(selectedItem.equals("Inspirational Quotes")){
                // Goes to inspirational quotes page.
                Intent inspirationalquotesPage = new Intent(ViewDiaryEntries.this, thoughtQuotes.class);
                inspirationalquotesPage.putExtra("quote_or_thought", 1);
                inspirationalquotesPage.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
                startActivity(inspirationalquotesPage);
            }
            else if(selectedItem.equals("Settings")){
                // Goes to settings page.
                Intent settingsPage = new Intent(ViewDiaryEntries.this, settings.class);
                settingsPage.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
                startActivity(settingsPage);
            }
        }
    });

    mainMenu_Dialog.show();
}

// For the settings button.
public void viewdiarypagelisttoSettings_butt(View v){
    // Goes to settings page.
    Intent settingsPage = new Intent(ViewDiaryEntries.this, settings.class);
    settingsPage.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
    startActivity(settingsPage);
}

// For new entry.
public void viewdiarypageaddEntry_butt(View v){
    // Opening up the diary add intent.
    Intent newdiaryEntry = new Intent(ViewDiaryEntries.this, newdiaryentry.class);
    startActivity(newdiaryEntry);
}
}

Here is my stack trace that I see:

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Object.toString()' on a null object reference
        at android.widget.ArrayAdapter.createViewFromResource(ArrayAdapter.java:401)
        at android.widget.ArrayAdapter.getView(ArrayAdapter.java:369)
        at android.widget.AbsSpinner.onMeasure(AbsSpinner.java:194)
        at android.widget.Spinner.onMeasure(Spinner.java:580)
        at android.support.v7.widget.AppCompatSpinner.onMeasure(AppCompatSpinner.java:407)
        at android.view.View.measure(View.java:18794)
        at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:715)
        at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:461)
        at android.view.View.measure(View.java:18794)
        at android.widget.ScrollView.measureChildWithMargins(ScrollView.java:1283)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
        at android.widget.ScrollView.onMeasure(ScrollView.java:340)
        at android.view.View.measure(View.java:18794)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
        at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:135)
        at android.view.View.measure(View.java:18794)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
        at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
        at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
        at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
        at android.view.View.measure(View.java:18794)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
        at android.view.View.measure(View.java:18794)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
        at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
        at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
        at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
        at android.view.View.measure(View.java:18794)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
        at com.android.internal.policy.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2643)
        at android.view.View.measure(View.java:18794)
        at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2100)
        at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1216)
        at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1452)
        at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1107)
        at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6013)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:858)
        at android.view.Choreographer.doCallbacks(Choreographer.java:670)
        at android.view.Choreographer.doFrame(Choreographer.java:606)
        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:844)
        at android.os.Handler.handleCallback(Handler.java:739)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:148)
        at android.app.ActivityThread.main(ActivityThread.java:5417)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

Any help towards a solution will be appreciated.

EDIT:

So after staring back and forth from the code between the database and the activity it interacts with, I managed to get it working again. Below is what I did in the exact order:

1. I realized that I had a date field that was receiving no data, rectified that.
2. Cleaned the project.
3. Restarted Android Studio (basically stopping all the operations of the development environment).
4. Uninstalled the app from my dev phone.
5. Restarted android studio and re-installed the app.
6. I somehow works =_=, yes it is magic.

Honestly I've no idea which step actually solved it. I'm guessing it was the date field in the database that was messing things up for me while it was receiving no data.

Answer 1

The array in your ArrayAdapter contains at least one entry that is null. There must be no nulls there.

The array is populated in getDiaryDBDataList() so the problem is also there.

Answer 2

Late answer but, n my case, I changed the resources tag name from integer-array to string-array and it worked fine.