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;

import java.util.Map;

public class Note {
    private String documentId;
    private String title;
    private String description;
    private int priority;
    Map<String, Boolean> tags;

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

    public Note(String title, String description, int priority, Map<String, Boolean> tags) {
        this.title = title;
        this.description = description;
        this.priority = priority;
        this.tags = tags;
    }

    @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 Map<String, Boolean> getTags() {
        return tags;
    }
}

<?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" />

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

    <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.firebase.firestore.CollectionReference;
import com.google.firebase.firestore.FirebaseFirestore;
import com.google.firebase.firestore.QueryDocumentSnapshot;
import com.google.firebase.firestore.QuerySnapshot;

import java.util.HashMap;
import java.util.Map;

public class MainActivity extends AppCompatActivity {
    private EditText editTextTitle;
    private EditText editTextDescription;
    private EditText editTextPriority;
    private EditText editTextTags;
    private TextView textViewData;

    private FirebaseFirestore db = FirebaseFirestore.getInstance();
    private CollectionReference notebookRef = db.collection("Notebook");

    @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);
        editTextTags = findViewById(R.id.edit_text_tags);
        textViewData = findViewById(R.id.text_view_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());

        String tagInput = editTextTags.getText().toString();
        String[] tagArray = tagInput.split("\\s*,\\s*");
        Map<String, Boolean> tags = new HashMap<>();

        for (String tag : tagArray) {
            tags.put(tag, true);
        }

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

        notebookRef.document("14g7Y5YjuaRcmGAiikUi")
                .collection("Child Notes").add(note);
    }

    public void loadNotes(View v) {
        notebookRef.document("14g7Y5YjuaRcmGAiikUi")
                .collection("Child Notes").get()
                .addOnSuccessListener(new OnSuccessListener<QuerySnapshot>() {
                    @Override
                    public void onSuccess(QuerySnapshot queryDocumentSnapshots) {
                        String data = "";

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

                            String documentId = note.getDocumentId();

                            data += "ID: " + documentId;

                            for (String tag : note.getTags().keySet()) {
                                data += "\n-" + tag;
                            }

                            data += "\n\n";
                        }
                        textViewData.setText(data);
                    }
                });
    }
}