如何在上一个圆弧动画完成后渲染圆弧路径

问题描述

当我尝试在同一路径中渲染两个圆弧时，两个圆弧都同时渲染，但我需要在第一个圆弧的动画完成后渲染第二个圆弧。

我只想渲染第二个弧，因为它应该从第一个弧的末端开始并完成动画的其余部分（连续动画）。

预期结果	实际结果

我附上了下面的代码片段，任何人都可以帮我解决这个问题。

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

class _HomePageState extends State<HomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Container(
        child: Circle(),),);
  }
}

class Circle extends StatefulWidget {
  @override
  _CircleState createState() => _CircleState();
}

class _CircleState extends State<Circle> with SingleTickerProviderStateMixin {
  double? _fraction = 0.0;
  late Animation<double> _animation;
  late AnimationController _controller;
  @override
  void initState() {
    super.initState();

    _controller =
        AnimationController(duration: Duration(milliseconds: 5000),vsync: this);

    _animation = Tween(begin: 0.0,end: 1.0).animate(_controller)
      ..addListener(() {
        setState(() {
          _fraction = _animation.value;
        });
      });

    _controller.forward();
  }

  @override
  Widget build(BuildContext context) {
    return Container(
      child: Center(
        child: Padding(
            padding: const EdgeInsets.all(24.0),child: CustomPaint(
              painter: CirclePainter(fraction: _fraction!),);
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }
}

class CirclePainter extends CustomPainter {
  final double? fraction;
  late Paint _circlePaint;

  CirclePainter({this.fraction}) {
    _circlePaint = Paint()
      ..color = Colors.red
      ..style = PaintingStyle.fill;
  }
  final Paint _paint = Paint()
  ..color = Colors.black
  ..style = PaintingStyle.stroke
  ..strokeWidth = 3;

  @override
  void paint(Canvas canvas,Size size) {
    final Path path = Path();
    path.addArc(
      Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 131.0909090909091),_degreesToradians(-90).todouble(),(_degreesToradians(269.999 * fraction!).todouble() - _degreesToradians(-90).todouble()));
    path.arcTo(
      Rect.fromCircle(center: Offset(size.width/2,radius: 42.32727272727273),_degreesToradians(269.999 * fraction!).todouble(),_degreesToradians(-90).todouble() - _degreesToradians((269.999) * fraction!).todouble(),false);
    path.addArc(
      Rect.fromCircle(center: Offset(size.width/2,(_degreesToradians(179.999 * fraction!).todouble() - _degreesToradians(-90).todouble()));
    path.arcTo(
      Rect.fromCircle(center: Offset(size.width/2,_degreesToradians(179.999 * fraction!).todouble(),_degreesToradians(-90).todouble() - _degreesToradians((179.999) * fraction!).todouble(),false);
  canvas.drawPath(path,_circlePaint);
  canvas.drawPath(path,_paint);
  }

  @override
  bool shouldRepaint(CirclePainter oldDelegate) {
    return oldDelegate.fraction != fraction;
  }
}
num _degreesToradians(num deg) => deg * (pi / 180);

预期：

解决方法

你可以这样做，第一个角是起始角，第二个角是终止角。你可以随意调整其他东西，但要获得旋转的效果，你需要不断改变结束角度。

我不想让笔尖变圆，你可以放 StrokeCap.butt

这个弧度函数的库是 vector_math。

 _path.addArc(Rect.fromLTWH(0,size.width,size.height),vm.radians(-90),vm.radians(90));

    canvas.drawPath(
        _path,Paint()
          ..strokeCap = StrokeCap.round
          ..strokeWidth = 40
          ..style = PaintingStyle.stroke);

对于第二个开始，您可以再次使用与我在上面代码中编写的相同的概念，并结合交错动画。

 final Animation<double> firstAnimation=
        Tween<double>(begin: 0,end: 1).animate(CurvedAnimation(
      parent: animationController,curve: Interval(0,0.5,curve: Curves.easeIn),));

final Animation<double> secondAnimation=
        Tween<double>(begin: 0,curve: Interval(0.5,1,));