Mobile Reminder app

MainActivity.java

Code Snippet: Main Activity Setup

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

    database = ReminderDatabase.getInstance(this);
    reminderList = new ArrayList<>();

    recyclerView = findViewById(R.id.recyclerView);
    recyclerView.setLayoutManager(new LinearLayoutManager(this));

    adapter = new ReminderAdapter(reminderList, new ReminderAdapter.OnDeleteClickListener() {
        @Override
        public void onDeleteClick(Reminder reminder) {
            deleteReminder(reminder);
        }
    });
    recyclerView.setAdapter(adapter);

    loadReminders();

    Button addButton = findViewById(R.id.addButton);
    addButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            // Start AddReminderActivity
            Intent intent = new Intent(MainActivity.this, AddReminderActivity.class);
            startActivityForResult(intent, ADD_REMINDER_REQUEST);
        }
    });

    // Check and request alarm permission
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.S) {
        if (!alarmPermissionGranted()) {
            requestAlarmPermission();
        }
    }
}

Explanation:

• This snippet initializes the main activity, sets up the RecyclerView for displaying reminders, and sets up a button for adding new reminders.
• It also includes a check for the necessary alarm permissions on newer Android versions.

Code Snippet: Adding a Reminder

@Override
protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
    super.onActivityResult(requestCode, resultCode, data);

    if (requestCode == ADD_REMINDER_REQUEST && resultCode == RESULT_OK && data != null) {
        String name = data.getStringExtra("name");
        String date = data.getStringExtra("date");

        if (name != null && date != null) {
            Reminder reminder = new Reminder(name, date);

            new Thread(new Runnable() {
                @Override
                public void run() {
                    database.reminderDao().insert(reminder);
                    loadReminders();

                    try {
                        scheduleNotification(parseDate(date), name);
                    } catch (ParseException e) {
                        Log.e("MainActivity", "Failed to parse date", e);
                        runOnUiThread(new Runnable() {
                            @Override
                            public void run() {
                                Toast.makeText(MainActivity.this, "Failed to parse date", Toast.LENGTH_SHORT).show();
                            }
                        });
                    }
                }
            }).start();
        }
    }
}

Explanation:

• This code handles the result from the AddReminderActivity, creating a new Reminder object and saving it to the database.
• It also schedules a notification for the reminder.

Code Snippet: Scheduling a Notification

private void scheduleNotification(Date date, String name) {
    Calendar calendar = Calendar.getInstance();
    calendar.setTime(date);

    // Set time to midday (12:00 PM)
    calendar.set(Calendar.HOUR_OF_DAY, 12);
    calendar.set(Calendar.MINUTE, 0);
    calendar.set(Calendar.SECOND, 0);
    calendar.set(Calendar.MILLISECOND, 0);

    // Subtract 1 day
    calendar.add(Calendar.DAY_OF_YEAR, -1);

    // Create an intent for NotificationReceiver
    Intent notificationIntent = new Intent(this, NotificationReceiver.class);
    notificationIntent.putExtra("name", name);

    // Create a PendingIntent
    PendingIntent pendingIntent = PendingIntent.getBroadcast(this, NOTIFICATION_ID,
            notificationIntent, PendingIntent.FLAG_UPDATE_CURRENT | PendingIntent.FLAG_IMMUTABLE);

    // Get AlarmManager
    AlarmManager alarmManager = (AlarmManager) getSystemService(Context.ALARM_SERVICE);
    if (alarmManager != null) {
        // Schedule the alarm
        alarmManager.setExact(AlarmManager.RTC_WAKEUP, calendar.getTimeInMillis(), pendingIntent);
    }
}

Explanation:

• This function schedules a notification to be triggered at midday, one day before the specified date.

Code Snippet: Deleting a Reminder

private void deleteReminder(Reminder reminder) {
    new Thread(new Runnable() {
        @Override
        public void run() {
            database.reminderDao().delete(reminder);
            loadReminders();

            // Optionally, cancel the scheduled notification for this reminder
            cancelNotification(reminder);
        }
    }).start();
}

Explanation:

• This method deletes a reminder from the database and cancels the associated notification.

Code Snippet: Requesting Alarm Permissions

private boolean alarmPermissionGranted() {
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.S) {
        return getSystemService(AlarmManager.class).canScheduleExactAlarms();
    }
    return true;
}

private void requestAlarmPermission() {
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.S) {
        Intent intent = new Intent();
        intent.setAction(Settings.ACTION_REQUEST_SCHEDULE_EXACT_ALARM);
        startActivity(intent);
    }
}

Explanation:

• These methods check if the app has the required permission to schedule exact alarms and request it if not granted.

ReminderAdapter.java

Code Snippet: Adapter with Delete Button

public class ReminderAdapter extends RecyclerView.Adapter<ReminderAdapter.ReminderViewHolder> {

    private List<Reminder> reminders;
    private OnDeleteClickListener deleteClickListener;

    public interface OnDeleteClickListener {
        void onDeleteClick(Reminder reminder);
    }

    public ReminderAdapter(List<Reminder> reminders, OnDeleteClickListener deleteClickListener) {
        this.reminders = reminders;
        this.deleteClickListener = deleteClickListener;
    }

    @NonNull
    @Override
    public ReminderViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View itemView = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.item_list, parent, false);
        return new ReminderViewHolder(itemView);
    }

    @Override
    public void onBindViewHolder(@NonNull ReminderViewHolder holder, int position) {
        Reminder reminder = reminders.get(position);
        holder.nameTextView.setText(reminder.getName());
        holder.dateTextView.setText(reminder.getDate());
        holder.deleteButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                deleteClickListener.onDeleteClick(reminder);
            }
        });
    }

    @Override
    public int getItemCount() {
        return reminders.size();
    }

    class ReminderViewHolder extends RecyclerView.ViewHolder {
        TextView nameTextView;
        TextView dateTextView;
        Button deleteButton;

        public ReminderViewHolder(@NonNull View itemView) {
            super(itemView);
            nameTextView = itemView.findViewById(R.id.nameTextView);
            dateTextView = itemView.findViewById(R.id.dateTextView);
            deleteButton = itemView.findViewById(R.id.deleteButton);
        }
    }
}

Explanation:

• The ReminderAdapter class binds the reminder data to the RecyclerView and sets up a click listener for the delete button.

item_list.xml

Code Snippet: Reminder Item Layout

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

    <TextView
        android:id="@+id/nameTextView"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:textSize="18sp" />

    <TextView
        android:id="@+id/dateTextView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="16sp" />

    <Button
        android:id="@+id/deleteButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Delete" />

</LinearLayout>

Explanation:

• This XML layout defines how each reminder item is displayed in the RecyclerView, with the reminder’s name, date, and a delete button aligned horizontally.

By breaking down the code into smaller, well-documented sections, you can make it easier for readers to understand the structure and functionality of your app.