rive-flutter/example/lib/example_animation.dart

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

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

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

class _ExampleAnimationState extends State<ExampleAnimation> {
  void _togglePlay() {
    if (_controller == null) {
      return;
    }
    setState(() => _controller!.isActive = !_controller!.isActive);
  }

  /// Tracks if the animation is playing by whether 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/dino.riv').then(
      (data) async {
        // Load the RiveFile from the binary data.
        final file = RiveFile.import(data);

        // The artboard is the root of the animation and gets drawn in the
        // Rive widget.
        final 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('Run'));
        setState(() => _riveArtboard = artboard);
      },
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Animation Example'),
      ),
      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,
        ),
      ),
    );
  }
}