老孟导读：此篇文章是 Flutter 动画系列文章第五篇，本文介绍2个自定义动画：涟漪和雷达扫描效果。
涟漪
实现涟漪动画效果如下：
此动画通过 CustomPainter 绘制配合 AnimationController 动画控制实现，定义动画控制部分：
class WaterRipple extends StatefulWidget {
final int count;
final Color color;
const WaterRipple({Key key, this.count = 3, this.color = const Color(0xFF0080ff)}) : super(key: key);
@override
_WaterRippleState createState() => _WaterRippleState();
}
class _WaterRippleState extends State<WaterRipple>
with SingleTickerProviderStateMixin {
AnimationController _controller;
@override
void initState() {
_controller =
AnimationController(vsync: this, duration: Duration(milliseconds: 2000))
..repeat();
super.initState();
}
@override
void dispose() {
_controller.dispose();
super.dispose();
}
@override
Widget build(BuildContext context) {
return AnimatedBuilder(
animation: _controller,
builder: (context, child) {
return CustomPaint(
painter: WaterRipplePainter(_controller.value,count: widget.count,color: widget.color),
);
},
);
}
}
count 和 color 分别代表水波纹的数量和颜色。
WaterRipplePainter 定义如下：
class WaterRipplePainter extends CustomPainter {
final double progress;
final int count;
final Color color;
Paint _paint = Paint()..style = PaintingStyle.fill;
WaterRipplePainter(this.progress,
{this.count = 3, this.color = const Color(0xFF0080ff)});
@override
void paint(Canvas canvas, Size size) {
double radius = min(size.width / 2, size.height / 2);
for (int i = count; i >= 0; i--) {
final double opacity = (1.0 - ((i + progress) / (count + 1)));
final Color _color = color.withOpacity(opacity);
_paint..color = _color;
double _radius = radius * ((i + progress) / (count + 1));
canvas.drawCircle(
Offset(size.width / 2, size.height / 2), _radius, _paint);
}
}
@override
bool shouldRepaint(CustomPainter oldDelegate) {
return true;
}
}
重点是 paint 方法，根据动画进度计算颜色的透明度和半径。
使用如下：
class WaterRipplePage extends StatelessWidget {
@override
Widget build(BuildContext context) {
return Scaffold(
body: Center(
child: Container(height: 200, width: 200, child: WaterRipple())),
);
}
}
雷达扫描
实现雷达扫描效果：
此效果分为两部分：中间的 logo 图片和扫描部分。
中间的 logo 图片
中间的 logo 图片边缘有阴影效果，像是太阳发光一样，实现：
Container(
height: 70.0,
width: 70.0,
decoration: BoxDecoration(
color: Colors.grey,
image: DecorationImage(
image: AssetImage('assets/images/logo.png')),
shape: BoxShape.circle,
boxShadow: [
BoxShadow(
color: Colors.white.withOpacity(.5),
blurRadius: 5.0,
spreadRadius: 3.0,
),
]),
)
扫描
定义雷达扫描的动画控制器：
class RadarView extends StatefulWidget {
@override
_RadarViewState createState() => _RadarViewState();
}
class _RadarViewState extends State<RadarView>
with SingleTickerProviderStateMixin {
AnimationController _controller;
Animation<double> _animation;
@override
void initState() {
_controller =
AnimationController(vsync: this, duration: Duration(seconds: 5));
_animation = Tween(begin: .0, end: pi * 2).animate(_controller);
_controller.repeat();
super.initState();
}
@override
void dispose() {
_controller.dispose();
super.dispose();
}
@override
Widget build(BuildContext context) {
return AnimatedBuilder(
animation: _animation,
builder: (context, child) {
return CustomPaint(
painter: RadarPainter(_animation.value),
);
},
);
}
}
RadarPainter 定义如下：
class RadarPainter extends CustomPainter {
final double angle;
Paint _bgPaint = Paint()
..color = Colors.white
..strokeWidth = 1
..style = PaintingStyle.stroke;
Paint _paint = Paint()..style = PaintingStyle.fill;
int circleCount = 3;
RadarPainter(this.angle);
@override
void paint(Canvas canvas, Size size) {
var radius = min(size.width / 2, size.height / 2);
canvas.drawLine(Offset(size.width / 2, size.height / 2 - radius),
Offset(size.width / 2, size.height / 2 + radius), _bgPaint);
canvas.drawLine(Offset(size.width / 2 - radius, size.height / 2),
Offset(size.width / 2 + radius, size.height / 2), _bgPaint);
for (var i = 1; i <= circleCount; ++i) {
canvas.drawCircle(Offset(size.width / 2, size.height / 2),
radius * i / circleCount, _bgPaint);
}
_paint.shader = ui.Gradient.sweep(
Offset(size.width / 2, size.height / 2),
[Colors.white.withOpacity(.01), Colors.white.withOpacity(.5)],
[.0, 1.0],
TileMode.clamp,
.0,
pi / 12);
canvas.save();
double r = sqrt(pow(size.width, 2) + pow(size.height, 2));
double startAngle = atan(size.height / size.width);
Point p0 = Point(r * cos(startAngle), r * sin(startAngle));
Point px = Point(r * cos(angle + startAngle), r * sin(angle + startAngle));
canvas.translate((p0.x - px.x) / 2, (p0.y - px.y) / 2);
canvas.rotate(angle);
canvas.drawArc(
Rect.fromCircle(
center: Offset(size.width / 2, size.height / 2), radius: radius),
0,
pi / 12,
true,
_paint);
canvas.restore();
}
@override
bool shouldRepaint(CustomPainter oldDelegate) {
return true;
}
}
将两者结合在一起：
class RadarPage extends StatelessWidget {
@override
Widget build(BuildContext context) {
return Scaffold(
backgroundColor: Color(0xFF0F1532),
body: Stack(
children: [
Positioned.fill(
left: 10,
right: 10,
child: Center(
child: Stack(children: [
Positioned.fill(
child: RadarView(),
),
Positioned(
child: Center(
child: Container(
height: 70.0,
width: 70.0,
decoration: BoxDecoration(
color: Colors.grey,
image: DecorationImage(
image: AssetImage('assets/images/logo.png')),
shape: BoxShape.circle,
boxShadow: [
BoxShadow(
color: Colors.white.withOpacity(.5),
blurRadius: 5.0,
spreadRadius: 3.0,
),
]),
),
),
),
]),
),
)
],
));
}
}
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