Flutter - Flip animation - Flip a card over its right or left side based on the tap's location - flutter

Question

I've started playing with Flutter and now thinking about the best way how I can implement a card's flipping animation.
I found this flip_card package and I'm trying to adjust its source code to my needs.
Here is the app which I have now:
import 'dart:math';
import 'package:flutter/material.dart';
void main() => runApp(FlipAnimationApp());
class FlipAnimationApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
home: Scaffold(
appBar: AppBar(
title: Text("Flip animation"),
),
body: Center(
child: Container(
width: 200,
height: 200,
child: WidgetFlipper(
frontWidget: Container(
color: Colors.green[200],
child: Center(
child: Text(
"FRONT side.",
),
),
),
backWidget: Container(
color: Colors.yellow[200],
child: Center(
child: Text(
"BACK side.",
),
),
),
),
),
),
),
);
}
}
class WidgetFlipper extends StatefulWidget {
WidgetFlipper({
Key key,
this.frontWidget,
this.backWidget,
}) : super(key: key);
final Widget frontWidget;
final Widget backWidget;
#override
_WidgetFlipperState createState() => _WidgetFlipperState();
}
class _WidgetFlipperState extends State<WidgetFlipper> with SingleTickerProviderStateMixin {
AnimationController controller;
Animation<double> _frontRotation;
Animation<double> _backRotation;
bool isFrontVisible = true;
#override
void initState() {
super.initState();
controller = AnimationController(duration: Duration(milliseconds: 500), vsync: this);
_frontRotation = TweenSequence(
<TweenSequenceItem<double>>[
TweenSequenceItem<double>(
tween: Tween(begin: 0.0, end: pi / 2).chain(CurveTween(curve: Curves.linear)),
weight: 50.0,
),
TweenSequenceItem<double>(
tween: ConstantTween<double>(pi / 2),
weight: 50.0,
),
],
).animate(controller);
_backRotation = TweenSequence(
<TweenSequenceItem<double>>[
TweenSequenceItem<double>(
tween: ConstantTween<double>(pi / 2),
weight: 50.0,
),
TweenSequenceItem<double>(
tween: Tween(begin: -pi / 2, end: 0.0).chain(CurveTween(curve: Curves.linear)),
weight: 50.0,
),
],
).animate(controller);
}
#override
void dispose() {
controller.dispose();
super.dispose();
}
#override
Widget build(BuildContext context) {
return Stack(
fit: StackFit.expand,
children: [
AnimatedCard(
animation: _backRotation,
child: widget.backWidget,
),
AnimatedCard(
animation: _frontRotation,
child: widget.frontWidget,
),
_tapDetectionControls(),
],
);
}
Widget _tapDetectionControls() {
return Stack(
fit: StackFit.expand,
children: <Widget>[
GestureDetector(
onTap: _leftRotation,
child: FractionallySizedBox(
widthFactor: 0.5,
heightFactor: 1.0,
alignment: Alignment.topLeft,
child: Container(
color: Colors.transparent,
),
),
),
GestureDetector(
onTap: _rightRotation,
child: FractionallySizedBox(
widthFactor: 0.5,
heightFactor: 1.0,
alignment: Alignment.topRight,
child: Container(
color: Colors.transparent,
),
),
),
],
);
}
void _leftRotation() {
_toggleSide();
}
void _rightRotation() {
_toggleSide();
}
void _toggleSide() {
if (isFrontVisible) {
controller.forward();
isFrontVisible = false;
} else {
controller.reverse();
isFrontVisible = true;
}
}
}
class AnimatedCard extends StatelessWidget {
AnimatedCard({
this.child,
this.animation,
});
final Widget child;
final Animation<double> animation;
#override
Widget build(BuildContext context) {
return AnimatedBuilder(
animation: animation,
builder: (BuildContext context, Widget child) {
var transform = Matrix4.identity();
transform.setEntry(3, 2, 0.001);
transform.rotateY(animation.value);
return Transform(
transform: transform,
alignment: Alignment.center,
child: child,
);
},
child: child,
);
}
}
Here is how it looks like:
What I'd like to achieve is to make the card flip over its right side if it was tapped on its right half and over its left side if it was tapped on its left half. If it is tapped several times in a row on the same half it should flip over the same side (not back and forth as it is doing now).
So the desired animation should behave as the following one from Quizlet app.

Answer 1

You should know when you tap on the right or left to change the animations dynamically, for that you could use a flag isRightTap. Then, you should invert the values of the Tweens if it has to rotate to one side or to the other.
And the side you should rotate would be:
Rotate to left if the front is visible and you tapped on the left, or, because the back animation is reversed, if the back is is visible and you tapped on the right
Otherwise, rotate to right
Here are the things I changed in _WidgetFlipperState from the code in the question:
_updateRotations(bool isRightTap) {
setState(() {
bool rotateToLeft = (isFrontVisible && !isRightTap) || !isFrontVisible && isRightTap;
_frontRotation = TweenSequence(
<TweenSequenceItem<double>>[
TweenSequenceItem<double>(
tween: Tween(begin: 0.0, end: rotateToLeft ? (pi / 2) : (-pi / 2))
.chain(CurveTween(curve: Curves.linear)),
weight: 50.0,
),
TweenSequenceItem<double>(
tween: ConstantTween<double>(rotateToLeft ? (-pi / 2) : (pi / 2)),
weight: 50.0,
),
],
).animate(controller);
_backRotation = TweenSequence(
<TweenSequenceItem<double>>[
TweenSequenceItem<double>(
tween: ConstantTween<double>(rotateToLeft ? (pi / 2) : (-pi / 2)),
weight: 50.0,
),
TweenSequenceItem<double>(
tween: Tween(begin: rotateToLeft ? (-pi / 2) : (pi / 2), end: 0.0)
.chain(CurveTween(curve: Curves.linear)),
weight: 50.0,
),
],
).animate(controller);
});
}
#override
void initState() {
super.initState();
controller =
AnimationController(duration: Duration(milliseconds: 500), vsync: this);
_updateRotations(true);
}
void _leftRotation() {
_toggleSide(false);
}
void _rightRotation() {
_toggleSide(true);
}
void _toggleSide(bool isRightTap) {
_updateRotations(isRightTap);
if (isFrontVisible) {
controller.forward();
isFrontVisible = false;
} else {
controller.reverse();
isFrontVisible = true;
}
}

Answer 2

import 'dart:math';
import 'package:flutter/material.dart';
void main() {
runApp(const MyApp());
}
class MyApp extends StatelessWidget {
const MyApp();
#override
Widget build(BuildContext context) {
return const MaterialApp(
debugShowCheckedModeBanner: false,
home: MyHomePage(),
);
}
}
class MyHomePage extends StatefulWidget {
const MyHomePage();
#override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
bool _toggler = true;
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(actions: [
TextButton(
onPressed: _onFlipCardPressed,
child: const Text('change', style: TextStyle(color: Colors.white)),
)
]),
body: Center(
child: SizedBox.square(
dimension: 140,
child: FlipCard(
toggler: _toggler,
frontCard: AppCard(title: 'Front'),
backCard: AppCard(title: 'Back'),
),
),
),
);
}
void _onFlipCardPressed() {
setState(() {
_toggler = !_toggler;
});
}
}
class AppCard extends StatelessWidget {
final String title;
const AppCard({
required this.title,
});
#override
Widget build(BuildContext context) {
return DecoratedBox(
decoration: BoxDecoration(
borderRadius: BorderRadius.circular(20.0),
color: Colors.deepPurple[400],
),
child: Center(
child: Text(
title,
style: const TextStyle(
fontSize: 40.0,
color: Colors.white,
),
textAlign: TextAlign.center,
),
),
);
}
}
class FlipCard extends StatelessWidget {
final bool toggler;
final Widget frontCard;
final Widget backCard;
const FlipCard({
required this.toggler,
required this.backCard,
required this.frontCard,
});
#override
Widget build(BuildContext context) {
return GestureDetector(
child: AnimatedSwitcher(
duration: const Duration(milliseconds: 800),
transitionBuilder: _transitionBuilder,
layoutBuilder: (widget, list) => Stack(children: [widget!, ...list]),
switchInCurve: Curves.ease,
switchOutCurve: Curves.ease.flipped,
child: toggler
? SizedBox(key: const ValueKey('front'), child: frontCard)
: SizedBox(key: const ValueKey('back'), child: backCard),
),
);
}
Widget _transitionBuilder(Widget widget, Animation<double> animation) {
final rotateAnimation = Tween(begin: pi, end: 0.0).animate(animation);
return AnimatedBuilder(
animation: rotateAnimation,
child: widget,
builder: (context, widget) {
final isFront = ValueKey(toggler) == widget!.key;
final rotationY = isFront ? rotateAnimation.value : min(rotateAnimation.value, pi * 0.5);
return Transform(
transform: Matrix4.rotationY(rotationY)..setEntry(3, 0, 0),
alignment: Alignment.center,
child: widget,
);
},
);
}
}

Answer 3

Try this code I've made some changes to your code, now the GestureDetector is divided equally in width on widget so when you tap on the left side of the box it will reverse the animation and if you tap on right side part it will forward the animation.
Widget _tapDetectionControls() {
return Flex(
direction: Axis.horizontal,
children: <Widget>[
Expanded(
flex: 1,
child: GestureDetector(
onTap: _leftRotation,
),
),
Expanded(
flex: 1,
child: GestureDetector(
onTap: _rightRotation,
),
),
],
);
}
void _leftRotation() {
controller.reverse();
}
void _rightRotation() {
controller.forward();
}