ListView doesn't appear in the MainActivty of my app (An image attached)

Question

After I save the note in my Android app, the note (or the ListView) of the note/s doesn't appear in the MainActivity. The MainActivity class of my app is:

package com.twitter.i_droidi.mynotes;

import android.app.AlertDialog;
import android.content.DialogInterface;
import android.content.Intent;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.ContextMenu;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Toast;
import java.util.List;

public class MainActivity extends ActionBarActivity implements AdapterView.OnItemClickListener {

    ListView lv;
    NotesDataSource nDS;
    List<NotesModel> notesList;

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

        nDS = new NotesDataSource(this);
        lv = (ListView) findViewById(R.id.lv);

        nDS.open();
        notesList = nDS.getAllNotes();
        nDS.close();

        String[] notes = new String[notesList.size()];

        for (int i = 0; i < notesList.size(); i++) {
            notes[i] = notesList.get(i).getTitle();
        }

        ArrayAdapter<String> adapter = new ArrayAdapter<String>(MainActivity.this, android.R.layout.simple_list_item_1,
                android.R.id.text1, notes);
        lv.setAdapter(adapter);

        registerForContextMenu(lv);
        lv.setOnItemClickListener(this);
    }

    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
        Intent nView = new Intent(this, Second.class);
        nView.putExtra("id", notesList.get(position).getId()); // Check...!!!
        startActivity(nView);
    }

    @Override
    public void onCreateContextMenu(ContextMenu menu, View v, ContextMenu.ContextMenuInfo menuInfo) {
        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.menu_delete, menu);
        super.onCreateContextMenu(menu, v, menuInfo);
    }

    @Override
    public boolean onContextItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.delete:
                nDS.open();
                nDS.deleteNote(lv.getId()); // Check...!!!
                nDS.close();
                Toast nDelete = Toast.makeText(this, "Deleted.", Toast.LENGTH_LONG);
                nDelete.show();
                return true;
        }
        return super.onContextItemSelected(item);
    }

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

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.mainMenuNewNote:
                Intent nNote = new Intent(this, Second.class);
                startActivity(nNote);
                return true;

            case R.id.mainMenuAbout:
                AlertDialog.Builder aboutDialog = new AlertDialog.Builder(this);
                aboutDialog.setTitle("About the app");
                aboutDialog.setMessage("The Simplest app for notes!\n\n" +
                        "Developed by: Abdulaziz\n" +
                        "Twitter: @i_Droidi\n" +
                        "Telegram: MrGlitch\n\n" +
                        "Special Thanks to who tested the app before upload it on Play Store and to who use it now! :)");
                aboutDialog.setIcon(R.mipmap.ic_launcher);
                aboutDialog.setPositiveButton("OK", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface aboutDialog, int witch) {
                        // Do Not Do Anything.
                    }
                });

                aboutDialog.show();
                return true;

            case R.id.mainMenuExit:
                AlertDialog.Builder exDialog = new AlertDialog.Builder(this);
                exDialog.setTitle("Exit?");
                exDialog.setMessage("Are you sure to exit?");
                exDialog.setIcon(R.mipmap.ic_launcher);
                exDialog.setNegativeButton("Yes", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface exDialog, int which) {
                        finish();
                    }
                });
                exDialog.setPositiveButton("No", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface exDialog, int which) {
                        // Do Not Do Anything.
                    }
                });

                exDialog.show();
                return true;
        }
        return super.onOptionsItemSelected(item);
    }
}

The activity_main (xml/layout file) of my app is:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content">

    <ListView
        android:id="@+id/lv"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"></ListView>

</LinearLayout>

The Second class of my app is:

package com.twitter.i_droidi.mynotes;

import android.app.AlertDialog;
import android.content.DialogInterface;
import android.content.Intent;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.widget.EditText;
import android.widget.Toast;

public class Second extends ActionBarActivity {

    NotesDataSource nDS;
    EditText noteTitle;
    EditText noteBody;
    int id;
    DB db;

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

        Intent in = getIntent();
        id = in.getIntExtra("id", 0);

        noteTitle = (EditText) findViewById(R.id.note_title);
        noteBody = (EditText) findViewById(R.id.note);
        nDS = new NotesDataSource(this);

        nDS.open();
        NotesModel note = nDS.getNote(id);
        nDS.close();

        noteTitle.setText(note.getTitle());
        noteBody.setText(note.getBody());
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.menu_second, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.secondMenuSave:
                if (!noteTitle.getText().toString().isEmpty() && !noteBody.getText().toString().isEmpty()) {
                    nDS.open();
                    nDS.updateNote(id, noteTitle.getText().toString(), noteBody.getText().toString());
                    nDS.close();
                    Toast nSave = Toast.makeText(this, "Saved.", Toast.LENGTH_LONG);
                    nSave.show();
                    finish();
                } else {
                    Toast notSave = Toast.makeText(this, "The title and content of the note CANNOT be empty!", Toast.LENGTH_LONG);
                    notSave.show();
                }
                return true;

            case R.id.secondMenuBack:
                AlertDialog.Builder baDialog = new AlertDialog.Builder(this);
                baDialog.setTitle("Back?");
                baDialog.setMessage("Do you want to back to the main page before saving the note?");
                baDialog.setIcon(R.mipmap.ic_launcher);
                baDialog.setNegativeButton("Yes", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface baDialog, int which) {
                        finish();
                    }
                });
                baDialog.setPositiveButton("No", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface baDialog, int which) {
                        // Do Not Do Anything.
                    }
                });

                baDialog.show();
                return true;
        }
        return super.onOptionsItemSelected(item);
    }
}

The NotesDataSource class of my app is:

package com.twitter.i_droidi.mynotes;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.util.Log;
import java.util.ArrayList;
import java.util.List;

public class NotesDataSource {

    DB myDB;
    SQLiteDatabase sql;

    String[] getAllColumns = new String[]{DB.ID, DB.TITLE, DB.BODY};

    public NotesDataSource(Context context) {
        myDB = new DB(context);
    }

    public void open() {
        try {
            sql = myDB.getWritableDatabase();
        } catch (Exception ex) {
            Log.d("Error in your database!", ex.getMessage());
        }
    }

    public void close() {
        sql.close();
    }

    public void createNote(String title, String body) {
        ContentValues note = new ContentValues();
        note.put(myDB.TITLE, title);
        note.put(myDB.BODY, body);
        sql.insert(myDB.TABLE_NAME, null, note);
    }

    public NotesModel getNote(int id) {
        NotesModel note = new NotesModel();

        Cursor cursor = sql.rawQuery("SELECT * FROM " + DB.TABLE_NAME + " WHERE " + DB.ID + " = ?", new String[]{id + ""});

        if (cursor.getCount() > 0) {
            cursor.moveToFirst();
            note.setId(cursor.getInt(0));
            note.setTitle(cursor.getString(1));
            note.setBody(cursor.getString(2));
            cursor.close();
        }
        return note;
    }

    public void updateNote(int id, String title, String body) {
        ContentValues note = new ContentValues();
        note.put(myDB.TITLE, title);
        note.put(myDB.BODY, body);
        sql.update(myDB.TABLE_NAME, note, myDB.ID + " = " + id, null);
    }

    public void deleteNote(Object id) {
        sql.delete(myDB.TABLE_NAME, myDB.ID + " = " + id, null);
    }

    public List<NotesModel> getAllNotes() {
        List<NotesModel> notesList = new ArrayList<NotesModel>();

        Cursor cursor = sql.query(myDB.TABLE_NAME, getAllColumns, null, null, null, null, null);
        cursor.moveToFirst();

        while (!cursor.isAfterLast()) {
            NotesModel notes = new NotesModel();
            notes.setId(cursor.getInt(0));
            notes.setTitle(cursor.getString(1));
            notes.setBody(cursor.getString(2));

            notesList.add(notes);
            cursor.moveToNext();
        }

        cursor.close();
        return notesList;
    }
}

The DB class of my app is:

package com.twitter.i_droidi.mynotes;

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

public class DB extends SQLiteOpenHelper {

    private static final String DB_NAME = "MyNotes";
    private static final int DB_VERSION = 1;

    public static final String TABLE_NAME = "MyNotes";
    public static final String ID = "id";
    public static final String TITLE = "title";
    public static final String BODY = "body";

    private static final String DB_CREATE = "create table " + TABLE_NAME + " (" + ID + " integer primary key autoincrement, " +
            TITLE + " text not null, " + BODY + " text not null)";

    public DB(Context context) {
        super(context, DB_NAME, null, DB_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(DB_CREATE);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
        onCreate(db);
    }
}

A screenshot of my app (MainActivity), after saving the note (Nothing shows!):

• A screenshot of my app, after saving the note (Nothing shows!)

How I can solve this problem?!

Or anyone can write the correct code?!

Thanks for helping me.

Answer 1

The problem is that the onCreate is only called once during the lifecycle. When you switch activities, the Main is simply hidden and paused. When you are returned to the activity, the onCreate does not fire again.

Override the onStart method and set your list adapter in there. It will be called right after the onCreate() and when you are returned to the view. Here is the Android lifecycle:

http://developer.android.com/training/basics/activity-lifecycle/starting.html

Answer 2

This answer assumes that your implementation of Second activity adds a new note to some global model and that the state of this model is reflected in the nDS object that you've already created in MainActivity (since onCreate() of MainActivity usually will not be called when you finish() Second).

You should definitely test that the above assumption is correct. If it is not, you could employ some form of Singleton design pattern for storing the data.

In order to reflect the changes into the ListView modify/add the following code in your MainActivity:

public class MainActivity extends ActionBarActivity implements AdapterView.OnItemClickListener {

ArrayAdapter<String> adapter;
NotesDataSource nDS;
List < NotesModel > notesList;

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

    nDS = new NotesDataSource(this);
    ListView lv = (ListView) findViewById(R.id.lv);

    nDS.open();
    notesList = nDS.getAllNotes();
    nDS.close();

    String[] notes = new String[notesList.size()];

    for (int i = 0; i < notesList.size(); i++) {
        notes[i] = notesList.get(i).getTitle();
    }

    adapter = new ArrayAdapter < String > (MainActivity.this, android.R.layout.simple_list_item_1,
    android.R.id.text1, notes);
    lv.setAdapter(adapter);

    registerForContextMenu(lv);
    lv.setOnItemClickListener(this);
}



@Override
protected void onResume() {
    super.onResume();

    nDS.open();
    notesList = nDS.getAllNotes();
    nDS.close();

    String[] notes = new String[notesList.size()];

    for (int i = 0; i < notesList.size(); i++) {
        notes[i] = notesList.get(i).getTitle();
    }

    adapter.clear();
    adapter.addAll(notes);
    adapter.notifyDataSetChanged();
}

// No changes in other methods ...

}

Additional note: it is very inefficient and error prone to maintain ArrayAdapter<String> and List<NotesModel>. It will be way better if you implement a custom ListAdapter. You can use something like this:

class CustomAdapter extends ArrayAdapter<NotesModel> {
    ...
}

Good tutorial on writing custom adapters can be found here.

Answer 3

I think there are two problem present in your code

1) First replace

public List<NotesModel> getAllNotes() {
        List<NotesModel> notesList = new ArrayList<NotesModel>();

        Cursor cursor = sql.query(myDB.TABLE_NAME, getAllColumns, null, null, null, null, null);
        cursor.moveToFirst();

        while (!cursor.isAfterLast()) {
            NotesModel notes = new NotesModel();
            notes.setId(cursor.getInt(0));
            notes.setTitle(cursor.getString(1));
            notes.setBody(cursor.getString(2));

            notesList.add(notes);
            cursor.moveToNext();
        }

        cursor.close();
        return notesList;
    }

with these

public List<NotesModel> getAllNotes() {
        List<NotesModel> notesList = new ArrayList<NotesModel>();

StringBuffer selectQuery = new StringBuffer();
selectQuery.append("SELECT * FROM "+myDB.TABLE_NAME+"");

        Cursor cursor = sql.rawQuery(selectQuery.toString(),null);

if (cursor != null && cursor.moveToFirst()) {
            do {
               NotesModel notes = new NotesModel();
            notes.setId(cursor.getInt(0));
            notes.setTitle(cursor.getString(1));
            notes.setBody(cursor.getString(2));

            notesList.add(notes);

            } while (cursor.moveToNext());
        }


        cursor.close();
        return notesList;
    }

2) Goto second class on list item click like this--

Intent nView = new Intent(this, Second.class);
        nView.putExtra("id", notesList.get(position).getId()); // Check...!!!
nView.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
        startActivity(nView);

and after adding note return back to MainActivity like this----

Intent nView = new Intent(this, MainActivity.class);
        nView.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
        startActivity(nView);

dont't use finish because it will end current task only and take out previous screen in stack without refreshing