Flutter--捕捉手势的弧度和角度

两个工具类

import 'package:flutter/material.dart';




class GestureAngleView extends StatelessWidget{

  final double angel;

  final Function(double angel, bool end) onChanged;
  final List<Widget> Function(BuildContext context, Size size, double radian)buildChildren;

  const GestureAngleView(this.angel, this.onChanged, this.buildChildren);

  @override
  Widget build(BuildContext context) {
    return GestureView(
      builder: (context, size) {
        return Stack(
          alignment:Alignment.center ,
          children: buildChildren(context, size, angel / 180 * pi),
        );
      },
      onChanged: (point, size, isEnd) {
        turn(point, size, isEnd);
      },
    );
  }


  void turn(Offset point, Size size, bool isEnd){
    var radian = getRadians(size.center(Offset.zero), point);
    var angel = getAngel(radian);
    onChanged(angel, isEnd);
  }


  double getRadius(Offset point, Offset center) {
    return sqrt(pow((point.dx - center.dx), 2) + pow(point.dy - center.dy, 2));
  }

  double getRadians(Offset center, Offset point) {
    var a = point.dx - center.dx;
    var b = center.dy - point.dy;
    double radians = atan2(b, a);
    return radians < 0 ? -radians : 2 * pi - radians;
  }


  double getAngel(double radian) {
    if(radian >= 2 * pi) {
      radian -= 2 * pi;
    }
    if(radian < 0) {
      radian += 2 * pi;
    }

    return (radian / pi) * 180;
  }


}




class GestureView extends StatefulWidget {

  final Function(Offset point, Size size, bool end) onChanged;
  final Widget Function(BuildContext context, Size size) builder;

  const GestureView({@required this.builder, @required this.onChanged, Key key}) : super(key: key);

  @override
  State<StatefulWidget> createState() => _GestureState();

}
class _GestureState extends State<GestureView> {

  Offset point;
  Size size;

  @override
  Widget build(BuildContext context) {
    return LayoutBuilder(builder: (BuildContext ctx, BoxConstraints constraints) {
      double width = constraints.maxWidth;
      double height = constraints.maxHeight;

      size = Size(width, height);

      return Center(child: GestureDetector(
        onHorizontalDragDown: (DragDownDetails details) => turn(details.globalPosition, details.localPosition),
        onHorizontalDragUpdate: (DragUpdateDetails details) => turn(details.globalPosition,  details.localPosition),
        onHorizontalDragEnd: (DragEndDetails details) => widget.onChanged(point, size, true),
        onVerticalDragDown: (DragDownDetails details) => turn(details.globalPosition,  details.localPosition),
        onVerticalDragUpdate: (DragUpdateDetails details) => turn(details.globalPosition,  details.localPosition),
        onVerticalDragEnd: (DragEndDetails details) => widget.onChanged(point, size, true),
        child: SizedBox(
          width: width,
          height: height,
          child: widget.builder(context, size),
        ),
      ),);
    },);

  }

  void turn(Offset globalPosition, Offset localPosition){
    point = localPosition;
    widget.onChanged(point, size, false);
  }

}