如何才能检测到TabBarView刚刚被拖走？

import 'package:flutter/material.dart';

class MyTabBarView extends StatefulWidget {
  @override
  _MyTabBarViewState createState() => _MyTabBarViewState();
}

class _MyTabBarViewState extends State<MyTabBarView> {
  bool isTabBarViewDragged = false;
  double initialPosition = 0.0;

  @override
  Widget build(BuildContext context) {
    return GestureDetector(
      onVerticalDragStart: (details) {
        initialPosition = details.globalPosition.dy;
      },
      onVerticalDragUpdate: (details) {
        double currentPosition = details.globalPosition.dy;
        if (currentPosition - initialPosition > 50) {
          setState(() {
            isTabBarViewDragged = true;
          });
        }
      },
      onVerticalDragEnd: (details) {
        setState(() {
          isTabBarViewDragged = false;
        });
      },
      child: Scaffold(
        appBar: AppBar(
          title: Text('TabBarView'),
        ),
        body: isTabBarViewDragged
            ? Center(
                child: Text('TabBarView被拖走了！'),
              )
            : TabBarView(
                children: [
                  // TabBarView的子页面
                ],
              ),
      ),
    );
  }
}