I have a problem with a practical application. I encountered a NullPointerException problem related to the toString method. Being new to Android app development, I don’t know the exact reason even after my research. So I ask someone who is more familiar with the stack trace to kindly help me.
Note. The error occurs when I click on the listview entry to access the edit page for the diary entry. However, it does not seem to get to the edit page at all.
Below you will find my activity code on which this happens and the stack trace.
Operation 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 with the solution would be appreciated.
EDIT:
Therefore, looking back and forth through the code between the database and the activity with which it interacts, I managed to get it to work again. The following is what I did in the exact order:
- I realized that I have a date field that does not receive data, this is fixed.
- Clear project.
- Rebooting Android Studio (basically, stopping all operations of the development environment).
- Removed the application from my phone.
- Rebooted Android studio and reinstalling the application.
- I somehow work = _ =, yes, this is magic.
Honestly, I have no idea which step I actually decided. I assume this is a date field in the database that was useless to me until it received any data.