```kotlin
import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import androidx.recyclerview.widget.RecyclerView
import androidx.room.Room
import com.google.android.material.floatingactionbutton.FloatingActionButton

// MainActivity class for the NotesApp
class MainActivity : AppCompatActivity() {

    private lateinit var db: AppDatabase // Database instance
    private lateinit var notesList: RecyclerView // RecyclerView to display notes list
    private lateinit var addButton: FloatingActionButton // Button to add a new note

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        // Initialize database
        db = Room.databaseBuilder(
            applicationContext,
            AppDatabase::class.java, "notes_database"
        ).build()

        // Find views by ID
        notesList = findViewById(R.id.notes_list)
        addButton = findViewById(R.id.add_button)

        // Set up RecyclerView and adapter for notes list
        val notesAdapter = NotesAdapter(this, db.noteDao())
        notesList.adapter = notesAdapter

        // Add click listener for adding a new note
        addButton.setOnClickListener {
            showCreateEditNoteDialog(null) { title, content ->
                val note = Note(id = 0, title = title, content = content)
                notesAdapter.insert(note)
            }
        }

        // Load initial data from the database
        notesAdapter.loadNotes()
    }

    // Function to show dialog for creating or editing a note
    private fun showCreateEditNoteDialog(note: Note?, onSave: (String, String) -> Unit) {
        // TODO: Implement dialog UI and logic
    }
}
```

```xml
<!-- activity_main.xml -->
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/notes_list"
        android:layout_width="0dp"
        android:layout_height="0dp"
        app:layout_constraintBottom_toTopOf="@+id/add_button"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <com.google.android.material.floatingactionbutton.FloatingActionButton
        android:id="@+id/add_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="16dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:srcCompat="@drawable/ic_add" />
</androidx.constraintlayout.widget.ConstraintLayout>
```

```xml
<!-- item_note.xml -->
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical"
    android:padding="16dp">

    <TextView
        android:id="@+id/note_title"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="18sp"
        tools:text="Note Title" />

    <TextView
        android:id="@+id/note_content"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="8dp"
        android:textSize="14sp"
        tools:text="Note Content" />
</LinearLayout>
```

```xml
<!-- dialog_create_edit_note.xml -->
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical"
    android:padding="16dp">

    <EditText
        android:id="@+id/note_title_input"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Title" />

    <EditText
        android:id="@+id/note_content_input"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="8dp"
        android:hint="Content" />
</LinearLayout>
```
```kotlin
import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import androidx.recyclerview.widget.RecyclerView
import androidx.room.Room
import com.google.android.material.floatingactionbutton.FloatingActionButton

// MainActivity class for the NotesApp
class MainActivity : AppCompatActivity() {

    private lateinit var db: AppDatabase // Database instance
    private lateinit var notesList: RecyclerView // RecyclerView to display notes list
    private lateinit var addButton: FloatingActionButton // Button to add a new note

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        // Initialize database
        db = Room.databaseBuilder(
            applicationContext,
            AppDatabase::class.java, "notes_database"
        ).build()

        // Find views by ID
        notesList = findViewById(R.id.notes_list)
        addButton = findViewById(R.id.add_button)

        // Set up RecyclerView and adapter for notes list
        val notesAdapter = NotesAdapter(this, db.noteDao())
        notesList.adapter = notesAdapter

        // Add click listener for adding a new note
        addButton.setOnClickListener {
            showCreateEditNoteDialog(null) { title, content ->
                val note = Note(id = 0, title = title, content = content)
                notesAdapter.insert(note)
            }
        }

        // Load initial data from the database
        notesAdapter.loadNotes()
    }

    // Function to show dialog for creating or editing a note
    private fun showCreateEditNoteDialog(note: Note?, onSave: (String, String) -> Unit) {
        // TODO: Implement dialog UI and logic
    }
}
```

```xml
<!-- activity_main.xml -->
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/notes_list"
        android:layout_width="0dp"
        android:layout_height="0dp"
        app:layout_constraintBottom_toTopOf="@+id/add_button"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <com.google.android.material.floatingactionbutton.FloatingActionButton
        android:id="@+id/add_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="16dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:srcCompat="@drawable/ic_add" />
</androidx.constraintlayout.widget.ConstraintLayout>
```

```xml
<!-- item_note.xml -->
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical"
    android:padding="16dp">

    <TextView
        android:id="@+id/note_title"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="18sp"
        tools:text="Note Title" />

    <TextView
        android:id="@+id/note_content"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="8dp"
        android:textSize="14sp"
        tools:text="Note Content" />
</LinearLayout>
```

```xml
<!-- dialog_create_edit_note.xml -->
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical"
    android:padding="16dp">

    <EditText
        android:id="@+id/note_title_input"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Title" />

    <EditText
        android:id="@+id/note_content_input"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="8dp"
        android:hint="Content" />
</LinearLayout>
```