How to get data from Firestore and show it on `FlutterBuilder` or `StreamBuilder`

#flutter #dart #firebase #firestore

I'm learning Flutter. I was stacked when I got data from Firestore. So this is a solution to that.

I was confused that there were some deprecated methods and complicated handling of the return value.

Here are examples for using it with FutureBuilder and StreamBuilder.

※ I omitted some steps like Firebase.initializeApp() etc.

FutureBuilder (Read once at first)

import 'package:flutter/material.dart';
import 'package:cloud_firestore/cloud_firestore.dart';

class HogeApp extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
    // <1> Use FutureBuilder
    return FutureBuilder<QuerySnapshot>(
        // <2> Pass `Future<QuerySnapshot>` to future
        future: FirebaseFirestore.instance.collection('posts').get(),
        builder: (context, snapshot) {
          if (snapshot.hasData) {
            // <3> Retrieve `List<DocumentSnapshot>` from snapshot
            final List<DocumentSnapshot> documents = snapshot.data.docs;
            return ListView(
                children: documents
                    .map((doc) => Card(
                          child: ListTile(
                            title: Text(doc['text']),
                            subtitle: Text(doc['email']),
                          ),
                        ))
                    .toList());
          } else if (snapshot.hasError) {
            return Text('It's Error!');
          }
        });
  }
}

Use FutureBuilder
Pass Future<QuerySnapshot> to future FirebaseFirestore.instance.collection('posts').get() If you reference an old tutorial you might find getDocuments(), but it's deprecated. Now it is replaced with get()
Retrieve List<DocumentSnapshot> from a snapshot. You can use methods like map(). documents is also deprecated.

StreamBuilder (updating data continuously)

It is useful for apps like chatting which requires frequent updates.

import 'package:flutter/material.dart';
import 'package:cloud_firestore/cloud_firestore.dart';

class HogeApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    // <1> Use StreamBuilder
    return StreamBuilder<QuerySnapshot>(
        // <2> Pass `Stream<QuerySnapshot>` to stream
        stream: FirebaseFirestore.instance.collection('posts').snapshots(),
        builder: (context, snapshot) {
          if (snapshot.hasData) {
            // <3> Retrieve `List<DocumentSnapshot>` from snapshot
            final List<DocumentSnapshot> documents = snapshot.data.docs;
            return ListView(
                children: documents
                    .map((doc) => Card(
                          child: ListTile(
                            title: Text(doc['text']),
                            subtitle: Text(doc['email']),
                          ),
                        ))
                    .toList());
          } else if (snapshot.hasError) {
            return Text('It's Error!');
          }
        });
  }
}

Use StreamBuilder
Pass Stream<QuerySnapshot> to stream
FirebaseFirestore.instance.collection('posts'). snapshot()
Retrieve List<DocumentSnapshot> from a snapshot. This part is the same as FutureBuilder