[embedyt] https://www.youtube.com/watch?v=3WR4QAiVuCw[/embedyt]
Links & Dependenciesactivity_new_note.xmlNewNoteActivity.javaAndroidManifest.xmlNoteAdapter.javaMainActivity.javaactivity_main.xmlnote_item.xmlNote.javanew_note_menu.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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"
    android:orientation="vertical"
    android:padding="16dp"
    tools:context=".NewNoteActivity">

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

    <EditText
        android:id="@+id/edit_text_description"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Description"
        android:inputType="textMultiLine" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="16dp"
        android:text="Priority:"
        android:textAppearance="@android:style/TextAppearance.Medium" />

    <NumberPicker
        android:id="@+id/number_picker_priority"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

</LinearLayout>
package com.codinginflow.firebaseui_firestoreexample;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.widget.EditText;
import android.widget.NumberPicker;
import android.widget.Toast;

import com.google.firebase.firestore.CollectionReference;
import com.google.firebase.firestore.FirebaseFirestore;

public class NewNoteActivity extends AppCompatActivity {
    private EditText editTextTitle;
    private EditText editTextDescription;
    private NumberPicker numberPickerPriority;

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

        getSupportActionBar().setHomeAsUpIndicator(R.drawable.ic_close);
        setTitle("Add Note");

        editTextTitle = findViewById(R.id.edit_text_title);
        editTextDescription = findViewById(R.id.edit_text_description);
        numberPickerPriority = findViewById(R.id.number_picker_priority);

        numberPickerPriority.setMinValue(1);
        numberPickerPriority.setMaxValue(10);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        MenuInflater menuInflater = getMenuInflater();
        menuInflater.inflate(R.menu.new_note_menu, menu);
        return super.onCreateOptionsMenu(menu);
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
            case R.id.save_note:
                saveNote();
                return true;
            default:
                return super.onOptionsItemSelected(item);
        }
    }

    private void saveNote() {
        String title = editTextTitle.getText().toString();
        String description = editTextDescription.getText().toString();
        int priority = numberPickerPriority.getValue();

        if (title.trim().isEmpty() || description.trim().isEmpty()) {
            Toast.makeText(this, "Please insert a title and description", Toast.LENGTH_SHORT).show();
            return;
        }

        CollectionReference notebookRef = FirebaseFirestore.getInstance()
                .collection("Notebook");
        notebookRef.add(new Note(title, description, priority));
        Toast.makeText(this, "Note added", Toast.LENGTH_SHORT).show();
        finish();
    }
}
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.codinginflow.firebaseui_firestoreexample">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity
            android:name=".MainActivity"
            android:launchMode="singleTop">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity
            android:name=".NewNoteActivity"
            android:parentActivityName=".MainActivity" />
    </application>

</manifest>
package com.codinginflow.firebaseui_firestoreexample;

import android.support.annotation.NonNull;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import com.firebase.ui.firestore.FirestoreRecyclerAdapter;
import com.firebase.ui.firestore.FirestoreRecyclerOptions;
import com.google.firebase.firestore.DocumentSnapshot;

public class NoteAdapter extends FirestoreRecyclerAdapter<Note, NoteAdapter.NoteHolder> {
    private OnItemClickListener listener;

    public NoteAdapter(@NonNull FirestoreRecyclerOptions<Note> options) {
        super(options);
    }

    @Override
    protected void onBindViewHolder(@NonNull NoteHolder holder, int position, @NonNull Note model) {
        holder.textViewTitle.setText(model.getTitle());
        holder.textViewDescription.setText(model.getDescription());
        holder.textViewPriority.setText(String.valueOf(model.getPriority()));
    }

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

    public void deleteItem(int position) {
        getSnapshots().getSnapshot(position).getReference().delete();
    }

    class NoteHolder extends RecyclerView.ViewHolder {
        TextView textViewTitle;
        TextView textViewDescription;
        TextView textViewPriority;

        public NoteHolder(View itemView) {
            super(itemView);
            textViewTitle = itemView.findViewById(R.id.text_view_title);
            textViewDescription = itemView.findViewById(R.id.text_view_description);
            textViewPriority = itemView.findViewById(R.id.text_view_priority);

            itemView.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    int position = getAdapterPosition();
                    if (position != RecyclerView.NO_POSITION && listener != null) {
                        listener.onItemClick(getSnapshots().getSnapshot(position), position);
                    }
                }
            });
        }
    }

    public interface OnItemClickListener {
        void onItemClick(DocumentSnapshot documentSnapshot, int position);
    }

    public void setOnItemClickListener(OnItemClickListener listener) {
        this.listener = listener;
    }
}
package com.codinginflow.firebaseui_firestoreexample;

import android.content.Intent;
import android.support.design.widget.FloatingActionButton;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.helper.ItemTouchHelper;
import android.view.View;
import android.widget.Toast;

import com.firebase.ui.firestore.FirestoreRecyclerOptions;
import com.google.firebase.firestore.CollectionReference;
import com.google.firebase.firestore.DocumentSnapshot;
import com.google.firebase.firestore.FirebaseFirestore;
import com.google.firebase.firestore.Query;

public class MainActivity extends AppCompatActivity {
    private FirebaseFirestore db = FirebaseFirestore.getInstance();
    private CollectionReference notebookRef = db.collection("Notebook");

    private NoteAdapter adapter;

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

        FloatingActionButton buttonAddNote = findViewById(R.id.button_add_note);
        buttonAddNote.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                startActivity(new Intent(MainActivity.this, NewNoteActivity.class));
            }
        });

        setUpRecyclerView();
    }

    private void setUpRecyclerView() {
        Query query = notebookRef.orderBy("priority", Query.Direction.DESCENDING);

        FirestoreRecyclerOptions<Note> options = new FirestoreRecyclerOptions.Builder<Note>()
                .setQuery(query, Note.class)
                .build();

        adapter = new NoteAdapter(options);

        RecyclerView recyclerView = findViewById(R.id.recycler_view);
        recyclerView.setHasFixedSize(true);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        recyclerView.setAdapter(adapter);

        new ItemTouchHelper(new ItemTouchHelper.SimpleCallback(0,
                ItemTouchHelper.LEFT | ItemTouchHelper.RIGHT) {
            @Override
            public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, RecyclerView.ViewHolder target) {
                return false;
            }

            @Override
            public void onSwiped(RecyclerView.ViewHolder viewHolder, int direction) {
                adapter.deleteItem(viewHolder.getAdapterPosition());
            }
        }).attachToRecyclerView(recyclerView);

        adapter.setOnItemClickListener(new NoteAdapter.OnItemClickListener() {
            @Override
            public void onItemClick(DocumentSnapshot documentSnapshot, int position) {
                Note note = documentSnapshot.toObject(Note.class);
                String id = documentSnapshot.getId();
                String path = documentSnapshot.getReference().getPath();
                Toast.makeText(MainActivity.this,
                        "Position: " + position + " ID: " + id, Toast.LENGTH_SHORT).show();
            }
        });
    }

    @Override
    protected void onStart() {
        super.onStart();
        adapter.startListening();
    }

    @Override
    protected void onStop() {
        super.onStop();
        adapter.stopListening();
    }
}
<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout 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"
    tools:context=".MainActivity">

    <android.support.v7.widget.RecyclerView
        android:id="@+id/recycler_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

    <android.support.design.widget.FloatingActionButton
        android:id="@+id/button_add_note"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom|end"
        android:layout_margin="16dp"
        android:src="@drawable/ic_add" />

</android.support.design.widget.CoordinatorLayout>
<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_marginEnd="8dp"
    android:layout_marginStart="8dp"
    android:layout_marginTop="8dp"
    app:cardBackgroundColor="#FFFFE8">

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:padding="8dp">

        <TextView
            android:id="@+id/text_view_title"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentStart="true"
            android:layout_toStartOf="@id/text_view_priority"
            android:ellipsize="end"
            android:maxLines="1"
            android:text="Title"
            android:textAppearance="@style/TextAppearance.AppCompat.Large" />

        <TextView
            android:id="@+id/text_view_priority"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentEnd="true"
            android:layout_alignParentTop="true"
            android:text="1"
            android:textAppearance="@style/TextAppearance.AppCompat.Large" />

        <TextView
            android:id="@+id/text_view_description"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentStart="true"
            android:layout_below="@id/text_view_title"
            android:text="Description" />

    </RelativeLayout>

</android.support.v7.widget.CardView>
package com.codinginflow.firebaseui_firestoreexample;

public class Note {
    private String title;
    private String description;
    private int priority;

    public Note() {
        //empty constructor needed
    }

    public Note(String title, String description, int priority) {
        this.title = title;
        this.description = description;
        this.priority = priority;
    }

    public String getTitle() {
        return title;
    }

    public String getDescription() {
        return description;
    }

    public int getPriority() {
        return priority;
    }
}
<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">
    <item
        android:id="@+id/save_note"
        android:icon="@drawable/ic_save"
        android:title="Save"
        app:showAsAction="ifRoom" />
</menu>