rive-flutter/example/lib/main.dart

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:rive/rive.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> with SingleTickerProviderStateMixin {
  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      home: MyHomePage(),
    );
  }
}

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

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  void _togglePlay() {
    setState(() => _controller.isActive = !_controller.isActive);
  }

  /// We track if the animation is playing by whether or not the controller is
  /// running.
  bool get isPlaying => _controller?.isActive ?? false;

  Artboard _riveArtboard;
  RiveAnimationController _controller;
  @override
  void initState() {
    super.initState();

    // Load the animation file from the bundle, note that you could also
    // download this. The RiveFile just expects a list of bytes.
    rootBundle.load('assets/colors_juice.riv').then(
      (data) async {
        var file = RiveFile();
        // Load the RiveFile from the binary data.
        var success = file.import(data);
        if (success) {
          // The artboard is the root of the animation and is what gets drawn
          // into the Rive widget.
          var artboard = file.mainArtboard;
          // Add a controller to play back a known animation on the main/default
          // artboard.We store a reference to it so we can toggle playback.
          artboard.addController(
            _controller = SimpleAnimation('walk'),
          );
          setState(() => _riveArtboard = artboard);
        }
      },
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: _riveArtboard == null
            ? const SizedBox()
            : Rive(artboard: _riveArtboard),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _togglePlay,
        tooltip: isPlaying ? 'Pause' : 'Play',
        child: Icon(
          isPlaying ? Icons.pause : Icons.play_arrow,
        ),
      ),
    );
  }
}