genui-workshop-step-4

name	genui_workshop_step_4
description	Execute Step 4 of the GenUI Workshop, setting up the GenUI scaffolding and initial chat interface.

GenUI Workshop - Step 4

Goal: Execute Step 4 of the GenUI workshop.

Instructions: Use your code editing tools to create or overwrite the following files in the project.

1. Create lib/genui_utils.dart:

sealed class ConversationItem {}

class TextItem extends ConversationItem {
  final String text;
  final bool isUser;
  TextItem({required this.text, this.isUser = false});
}

const systemInstruction = '''
  ## PERSONA
  You are a meteorologist.

  ## GOAL
  Work with me to produce of weather forecasts.

  ## RULES

  Do not offer opinions unless I ask for them.

  ## PROCESS
  ### Planning
  *   Ask me for a location to check the weather.
  *   Follow up and ask for a date if not provided.
  *   Synthesize a list of weather forecasts from the provided information.
  *   Where available, you will use tool calls to retreive the info (not implemented yet)
  *   Advise if you are pulling the data from a real source or making it up.
  *   Ask clarifying questions if you need to.
  *   Respond to my suggestions for changes to date or location, if I have any.
''';

2. Create lib/message_bubble.dart:

import 'package:flutter/material.dart';

class MessageBubble extends StatelessWidget {
  final String text;
  final bool isUser;

  const MessageBubble({super.key, required this.text, required this.isUser});

  @override
  Widget build(BuildContext context) {
    final theme = Theme.of(context);
    final colorScheme = theme.colorScheme;

    final bubbleColor = isUser
        ? colorScheme.primary
        : colorScheme.surfaceContainerHighest;

    final textColor = isUser
        ? colorScheme.onPrimary
        : colorScheme.onSurfaceVariant;

    return Padding(
      padding: const EdgeInsets.symmetric(vertical: 6.0, horizontal: 8.0),
      child: Column(
        crossAxisAlignment: isUser
            ? CrossAxisAlignment.end
            : CrossAxisAlignment.start,
        children: [
          Row(
            mainAxisAlignment: isUser
                ? MainAxisAlignment.end
                : MainAxisAlignment.start,
            children: [
              Flexible(
                child: Container(
                  padding: const EdgeInsets.symmetric(
                    horizontal: 16.0,
                    vertical: 12.0,
                  ),
                  decoration: BoxDecoration(
                    color: bubbleColor,
                    borderRadius: BorderRadius.only(
                      topLeft: const Radius.circular(20),
                      topRight: const Radius.circular(20),
                      bottomLeft: Radius.circular(isUser ? 20 : 0),
                      bottomRight: Radius.circular(isUser ? 0 : 20),
                    ),
                    boxShadow: [
                      BoxShadow(
                        color: Colors.black.withAlpha(20),
                        blurRadius: 4,
                        offset: const Offset(0, 2),
                      ),
                    ],
                    gradient: isUser
                        ? LinearGradient(
                            colors: [
                              colorScheme.primary,
                              colorScheme.primary.withAlpha(200),
                            ],
                            begin: Alignment.topLeft,
                            end: Alignment.bottomRight,
                          )
                        : null,
                  ),
                  child: Text(
                    text,
                    style: theme.textTheme.bodyLarge?.copyWith(
                      color: textColor,
                      height: 1.3,
                    ),
                  ),
                ),
              ),
            ],
          ),
          const SizedBox(height: 2),
        ],
      ),
    );
  }
}

3. Overwrite lib/main.dart with:

import 'package:flutter/material.dart';
import 'package:firebase_core/firebase_core.dart';
import 'package:firebase_ai/firebase_ai.dart';
import 'package:genui_workshop/message_bubble.dart';
import 'package:genui_workshop/genui_utils.dart';
import 'firebase_options.dart';

Future<void> main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp(options: DefaultFirebaseOptions.currentPlatform);
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Weather Today',
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.blue),
      ),
      home: const MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key});

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  final List<ConversationItem> _items = [];
  final _textController = TextEditingController();
  final _scrollController = ScrollController();
  late final ChatSession _chatSession;

  @override
  void initState() {
    super.initState();
    final model = FirebaseAI.googleAI().generativeModel(
      model: 'gemini-3.1-flash-lite',
    );
    _chatSession = model.startChat();
    _chatSession.sendMessage(Content.text(systemInstruction));
  }

  void _scrollToBottom() {
    WidgetsBinding.instance.addPostFrameCallback((_) {
      if (_scrollController.hasClients) {
        _scrollController.animateTo(
          _scrollController.position.maxScrollExtent,
          duration: const Duration(milliseconds: 300),
          curve: Curves.easeOut,
        );
      }
    });
  }

  @override
  void dispose() {
    _textController.dispose();
    _scrollController.dispose();
    super.dispose();
  }

  Future<void> _addMessage() async {
    final text = _textController.text;

    if (text.trim().isEmpty) {
      return;
    }
    _textController.clear();

    setState(() {
      _items.add(TextItem(text: text, isUser: true));
    });

    _scrollToBottom();

    final response = await _chatSession.sendMessage(Content.text(text));

    if (response.text?.isNotEmpty ?? false) {
      setState(() {
        _items.add(TextItem(text: response.text!, isUser: false));
      });
      _scrollToBottom();
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Theme.of(context).colorScheme.inversePrimary,
        title: const Text('Weather'),
      ),
      body: Column(
        children: [
          Expanded(
            child: ListView(
              controller: _scrollController,
              padding: const EdgeInsets.all(16),
              children: [
                for (final item in _items)
                  switch (item) {
                    TextItem() => MessageBubble(
                      text: item.text,
                      isUser: item.isUser,
                    ),
                  },
              ],
            ),
          ),
          SafeArea(
            child: Padding(
              padding: const EdgeInsets.symmetric(horizontal: 16.0),
              child: Row(
                children: [
                  Expanded(
                    child: TextField(
                      controller: _textController,
                      onSubmitted: (_) => _addMessage(),
                      decoration: const InputDecoration(
                        hintText: 'Enter a message',
                      ),
                    ),
                  ),
                  const SizedBox(width: 8),
                  ElevatedButton(
                    onPressed: _addMessage,
                    child: const Text('Send'),
                  ),
                ],
              ),
            ),
          ),
        ],
      ),
    );
  }
}