trifid_mobile/lib/components/SpecialButton.dart

import 'dart:io';

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

// This is a button that pushes the bare minimum onto you, it doesn't even respect button themes - unless you tell it to
class SpecialButton extends StatefulWidget {
  const SpecialButton({Key key, this.child, this.color, this.onPressed, this.useButtonTheme = false, this.decoration}) : super(key: key);

  final Widget child;
  final Color color;
  final bool useButtonTheme;
  final BoxDecoration decoration;

  final Function onPressed;

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

class _SpecialButtonState extends State<SpecialButton> with SingleTickerProviderStateMixin {
  @override
  Widget build(BuildContext context) {
    return Platform.isAndroid ? _buildAndroid() : _buildGeneric();
  }

  Widget _buildAndroid() {
    var textStyle;
    if (widget.useButtonTheme) {
      textStyle = Theme.of(context).textTheme.button;
    }

    return Material(
        textStyle: textStyle,
        child: Ink(
          decoration: widget.decoration,
          color: widget.color,
          child: InkWell(
            child: widget.child,
            onTap: widget.onPressed,
          )));
  }

  Widget _buildGeneric() {
    var textStyle = CupertinoTheme.of(context).textTheme.textStyle;
    if (widget.useButtonTheme) {
      textStyle = CupertinoTheme.of(context).textTheme.actionTextStyle;
    }

    return Container(
      decoration: widget.decoration,
      child: GestureDetector(
        behavior: HitTestBehavior.opaque,
        onTapDown: _handleTapDown,
        onTapUp: _handleTapUp,
        onTapCancel: _handleTapCancel,
        onTap: widget.onPressed,
        child: Semantics(
          button: true,
          child: FadeTransition(
            opacity: _opacityAnimation,
            child: DefaultTextStyle(style: textStyle, child: Container(child: widget.child, color: widget.color)),
          ),
        ),
      )
    );
  }

  // Eyeballed values. Feel free to tweak.
  static const Duration kFadeOutDuration = Duration(milliseconds: 10);
  static const Duration kFadeInDuration = Duration(milliseconds: 100);
  final Tween<double> _opacityTween = Tween<double>(begin: 1.0);

  AnimationController _animationController;
  Animation<double> _opacityAnimation;

  @override
  void initState() {
    super.initState();
    _animationController = AnimationController(
      duration: const Duration(milliseconds: 200),
      value: 0.0,
      vsync: this,
    );
    _opacityAnimation = _animationController.drive(CurveTween(curve: Curves.decelerate)).drive(_opacityTween);
    _setTween();
  }

  @override
  void didUpdateWidget(SpecialButton old) {
    super.didUpdateWidget(old);
    _setTween();
  }

  void _setTween() {
    _opacityTween.end = 0.4;
  }

  @override
  void dispose() {
    _animationController.dispose();
    _animationController = null;
    super.dispose();
  }

  bool _buttonHeldDown = false;

  void _handleTapDown(TapDownDetails event) {
    if (!_buttonHeldDown) {
      _buttonHeldDown = true;
      _animate();
    }
  }

  void _handleTapUp(TapUpDetails event) {
    if (_buttonHeldDown) {
      _buttonHeldDown = false;
      _animate();
    }
  }

  void _handleTapCancel() {
    if (_buttonHeldDown) {
      _buttonHeldDown = false;
      _animate();
    }
  }

  void _animate() {
    if (_animationController.isAnimating) {
      return;
    }

    final bool wasHeldDown = _buttonHeldDown;
    final TickerFuture ticker = _buttonHeldDown
        ? _animationController.animateTo(1.0, duration: kFadeOutDuration)
        : _animationController.animateTo(0.0, duration: kFadeInDuration);

    ticker.then<void>((void value) {
      if (mounted && wasHeldDown != _buttonHeldDown) {
        _animate();
      }
    });
  }
}