Flutter - Animation from bottom to top in CustomPainter - dart

Question

I'm trying to create an animation in a CustomPainter in which the animation starts from the bottom to up, but it's starting at the top.
When clicking on the FloatActionButton the rectangle should rise to the maximum height of the screen, and when tap again go back to the minimum size.
I can get the size of the screen but I'm not able to insert this animation from the bottom to up. can you help me?
import 'package:flutter/material.dart';
import 'dart:ui' as ui;
void main() {
runApp(new MaterialApp(home: new HomePage()));
}
class HomePage extends StatefulWidget {
#override
HomePageState createState() => new HomePageState();
}
class HomePageState extends State<HomePage> with TickerProviderStateMixin {
AnimationController _controller;
Animation<double> _animation;
bool upDown = true;
#override
void initState() {
_controller = new AnimationController(
vsync: this,
duration: const Duration(milliseconds: 180),
);
_animation = new CurvedAnimation(
parent: _controller,
curve: new Interval(0.0, 1.0, curve: Curves.linear),
);
}
#override
Widget build(BuildContext context) {
final ui.Size logicalSize = MediaQuery.of(context).size;
final double _width = logicalSize.width;
final double _height = logicalSize.height;
void _up(){
setState((){
if(upDown) {
upDown = false;
_controller.forward(from: 0.0);
} else {
upDown = true;
_controller.reverse(from: 1.0);
}
});
}
return new Scaffold(
body: new Stack(
children: <Widget>[
new Positioned(
bottom: 0.0,
child: new AnimatedBuilder(
animation: _animation,
builder: (BuildContext context, Widget child) {
return new Container(
height: _height,
child: new CustomPaint(
painter: new Sky(_width, _height * _animation.value),
//child: new Text('$_height '+ _animation.value.toString()),
),
);
},
),
),
new Positioned(
bottom: 16.0,
right: 16.0,
child: new FloatingActionButton(
backgroundColor: new Color(0xFFE57373),
child: new Icon(Icons.add),
onPressed: (){
_up();
},
)
)
]
)
);
}
}
class Sky extends CustomPainter {
final double _width;
double _rectHeight;
Sky(this._width, this._rectHeight);
#override
void paint(Canvas canvas, Size size) {
canvas.drawRect(
new Rect.fromLTRB(
0.0, 0.0, this._width, _rectHeight
),
new Paint()..color = new Color(0xFF0099FF),
);
}
#override
bool shouldRepaint(Sky oldDelegate) {
return _width != oldDelegate._width || _rectHeight != oldDelegate._rectHeight;
}
}

Answer 1

You can use an AnimatedBuilder to do this. Also, make sure that you provide a working implementation of shouldRepaint. Your upDown member variable should be a member of the State rather than part of the build function.
import 'package:flutter/material.dart';
import 'dart:ui' as ui;
void main() {
runApp(new MaterialApp(home: new HomePage()));
}
class HomePage extends StatefulWidget {
#override
HomePageState createState() => new HomePageState();
}
class HomePageState extends State<HomePage> with TickerProviderStateMixin {
AnimationController _controller;
Animation<double> _animation;
bool upDown = true;
#override
void initState() {
_controller = new AnimationController(
vsync: this,
duration: const Duration(milliseconds: 180),
);
_animation = new CurvedAnimation(
parent: _controller,
curve: new Interval(0.0, 1.0, curve: Curves.linear),
);
}
#override
Widget build(BuildContext context) {
final ui.Size logicalSize = MediaQuery.of(context).size;
final double _width = logicalSize.width;
final double _height = logicalSize.height;
void _up(){
setState((){
if(upDown) {
upDown = false;
_controller.forward(from: 0.0);
} else {
upDown = true;
_controller.reverse(from: 1.0);
}
});
}
return new Scaffold(
body: new Stack(
children: <Widget>[
new Positioned(
bottom: 0.0,
child: new AnimatedBuilder(
animation: _animation,
builder: (BuildContext context, Widget child) {
return new Container(
height: _height,
child: new CustomPaint(
painter: new Sky(_width, _height * _animation.value),
),
);
},
),
),
new Positioned(
bottom: 16.0,
right: 16.0,
child: new FloatingActionButton(
backgroundColor: new Color(0xFFE57373),
child: new Icon(Icons.add),
onPressed: (){
_up();
},
)
)
]
)
);
}
}
class Sky extends CustomPainter {
final double _width;
double _rectHeight;
Sky(this._width, this._rectHeight);
#override
void paint(Canvas canvas, Size size) {
canvas.drawRect(
new Rect.fromLTRB(
0.0, size.height - _rectHeight, this._width, size.height
),
new Paint()..color = new Color(0xFF0099FF),
);
}
#override
bool shouldRepaint(Sky oldDelegate) {
return _width != oldDelegate._width || _rectHeight != oldDelegate._rectHeight;
}
}