import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('GestureDetector 手势识别（拖曳）- 手势竞争'),
        ),
        body: GestureCompetePage(),
      ),
    );
  }
}

// 手势竞争
// 在手势识别中 可以监听多个手势事件，但最终只有一个手势能够得到本次事件的处理权

class GestureCompetePage extends StatefulWidget {
  @override
  _GestureCompetePageState createState() => _GestureCompetePageState();
}

class _GestureCompetePageState extends State<GestureCompetePage> {
  double _top = 0.0;
  double _left = 0.0;
  @override
  Widget build(BuildContext context) {
    return Stack(
      children: [
        Positioned(
          top: _top,
          left: _left,
          child: GestureDetector(
            child: CircleAvatar(
              minRadius: 40,
              child: Text(
                "手势竞争",
                style: TextStyle(fontSize: 16),
              ),
            ),
            // 垂直方向拖曳更新
            onVerticalDragUpdate: (detail) {
              setState(() {
                _top += detail.delta.dy;
              });
            },
            // 水平方向拖曳更新
            onHorizontalDragUpdate: (detail) {
              setState(() {
                _left += detail.delta.dx;
              });
            },
          ),
        ),
      ],
    );
  }
}