Links & DependenciesNote.javaactivity_main.xmlMainActivity.java

Firebase setup guide with dependencies and console link:

firebase.google.com/docs/android/setup

package com.codinginflow.firestoreexampleproject;

import com.google.firebase.firestore.Exclude;

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

    public Note() {
        //public no-arg constructor needed
    }

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

    @Exclude
    public String getDocumentId() {
        return documentId;
    }

    public void setDocumentId(String documentId) {
        this.documentId = documentId;
    }

    public String getTitle() {
        return title;
    }

    public String getDescription() {
        return description;
    }

    public int getPriority() {
        return priority;
    }

    public void setPriority(int priority) {
        this.priority = priority;
    }
}

<?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="com.codinginflow.firestoreexampleproject.MainActivity">

    <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="text" />

    <EditText
        android:id="@+id/edit_text_priority"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Priority"
        android:inputType="number" />

    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="addNote"
        android:text="Add" />

    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="loadNotes"
        android:text="Load" />

    <android.support.v4.widget.NestedScrollView
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <TextView
            android:id="@+id/text_view_data"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textSize="20sp" />

    </android.support.v4.widget.NestedScrollView>
</LinearLayout>

package com.codinginflow.firestoreexampleproject;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;

import com.google.android.gms.tasks.OnSuccessListener;
import com.google.android.gms.tasks.Task;
import com.google.android.gms.tasks.Tasks;
import com.google.firebase.firestore.CollectionReference;
import com.google.firebase.firestore.DocumentReference;
import com.google.firebase.firestore.EventListener;
import com.google.firebase.firestore.FirebaseFirestore;
import com.google.firebase.firestore.FirebaseFirestoreException;
import com.google.firebase.firestore.QueryDocumentSnapshot;
import com.google.firebase.firestore.QuerySnapshot;

import java.util.List;

public class MainActivity extends AppCompatActivity {
    private static final String TAG = "MainActivity";

    private static final String KEY_TITLE = "title";
    private static final String KEY_DESCRIPTION = "description";

    private EditText editTextTitle;
    private EditText editTextDescription;
    private EditText editTextPriority;
    private TextView textViewData;

    private FirebaseFirestore db = FirebaseFirestore.getInstance();
    private CollectionReference notebookRef = db.collection("Notebook");
    private DocumentReference noteRef = db.document("Notebook/My First Note");

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

        editTextTitle = findViewById(R.id.edit_text_title);
        editTextDescription = findViewById(R.id.edit_text_description);
        editTextPriority = findViewById(R.id.edit_text_priority);
        textViewData = findViewById(R.id.text_view_data);
    }

    @Override
    protected void onStart() {
        super.onStart();
        notebookRef.addSnapshotListener(this, new EventListener<QuerySnapshot>() {
            @Override
            public void onEvent(QuerySnapshot queryDocumentSnapshots, FirebaseFirestoreException e) {
                if (e != null) {
                    return;
                }

                String data = "";

                for (QueryDocumentSnapshot documentSnapshot : queryDocumentSnapshots) {
                    Note note = documentSnapshot.toObject(Note.class);
                    note.setDocumentId(documentSnapshot.getId());

                    String documentId = note.getDocumentId();
                    String title = note.getTitle();
                    String description = note.getDescription();
                    int priority = note.getPriority();

                    data += "ID: " + documentId
                            + "\nTitle: " + title + "\nDescription: " + description
                            + "\nPriority: " + priority + "\n\n";
                }

                textViewData.setText(data);
            }
        });
    }

    public void addNote(View v) {
        String title = editTextTitle.getText().toString();
        String description = editTextDescription.getText().toString();

        if (editTextPriority.length() == 0) {
            editTextPriority.setText("0");
        }

        int priority = Integer.parseInt(editTextPriority.getText().toString());

        Note note = new Note(title, description, priority);

        notebookRef.add(note);
    }

    public void loadNotes(View v) {
        Task task1 = notebookRef.whereLessThan("priority", 2)
                .orderBy("priority")
                .get();

        Task task2 = notebookRef.whereGreaterThan("priority", 2)
                .orderBy("priority")
                .get();

        Task<List<QuerySnapshot>> allTasks = Tasks.whenAllSuccess(task1, task2);
        allTasks.addOnSuccessListener(new OnSuccessListener<List<QuerySnapshot>>() {
            @Override
            public void onSuccess(List<QuerySnapshot> querySnapshots) {
                String data = "";

                for (QuerySnapshot queryDocumentSnapshots : querySnapshots) {
                    for (QueryDocumentSnapshot documentSnapshot : queryDocumentSnapshots) {
                        Note note = documentSnapshot.toObject(Note.class);
                        note.setDocumentId(documentSnapshot.getId());

                        String documentId = note.getDocumentId();
                        String title = note.getTitle();
                        String description = note.getDescription();
                        int priority = note.getPriority();

                        data += "ID: " + documentId
                                + "\nTitle: " + title + "\nDescription: " + description
                                + "\nPriority: " + priority + "\n\n";
                    }
                }

                textViewData.setText(data);
            }
        });
    }
}