animated_rotation_button_full_code.dart

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

void main() {
  runApp(
    MaterialApp(
      theme: ThemeData.dark(),
      home: Scaffold(body: HomePage()),
      debugShowCheckedModeBanner: false,
    ),
  );
}

class HomePage extends StatefulWidget {
  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  double _angle = 0;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: AnimatedRotationButton(
          child: Text(
            'Clique me!',
            style: TextStyle(color: Colors.white),
          ),
          angle: _angle,
          onPressed: () {
            setState(() {
              _angle += 45 * pi / 180;
            });
          },
        ),
      ),
    );
  }
}

class AnimatedRotationButton extends ImplicitlyAnimatedWidget {
  final Widget child;
  final double angle;
  final Function onPressed;

  const AnimatedRotationButton({
    Key key,
    this.child,
    this.angle,
    this.onPressed,
  }) : super(key: key, duration: const Duration(milliseconds: 300));

  @override
  ImplicitlyAnimatedWidgetState createState() => _AnimatedRotationButtonState();
}

class _AnimatedRotationButtonState
    extends AnimatedWidgetBaseState<AnimatedRotationButton> {
  Tween<double> _angleTween;

  @override
  void forEachTween(visitor) {
    _angleTween = visitor(
      _angleTween,
      widget.angle,
      (value) => Tween<double>(begin: value),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Transform.rotate(
      angle: _angleTween.evaluate(animation),
      child: RaisedButton(
        color: Colors.blue,
        child: widget.child,
        onPressed: widget.onPressed,
      ),
    );
  }
}