How can i detect the contact of the finger with a specific widget (after being swiping from another point )

Question

lets say the user put his finger on the screen , then swipe his finger to the specific widget How can i detect when the finger access to that widget

this is simple code

import 'package:flutter/material.dart';

class App extends StatefulWidget {
  const App({Key? key}) : super(key: key);

  @override
  State<App> createState() => _AppState();
}

class _AppState extends State<App> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(),
      body: Center(
        child: Column(
          children: [
            const SizedBox(height: 20,),
            Container(
              alignment: Alignment.center,
              color: Colors.green,
              height: 200,
                width: 200,
                child: Text('let me know when you arrive me',style: TextStyle(color: Colors.white),)
            ),
            const Spacer(),
            Container(
                alignment: Alignment.center,
                color: Colors.red,
                height: 200,
                width: 200,
                child: Text('start pont here',style: TextStyle(color: Colors.white))
            ),
            const SizedBox(height: 20,)
          ],

        ),
      ),
    );
  }
}

Note: i have read in flutter doc that there Draggable class which handle this case and to be honest it is doing very well but opportunity this is not fit my code

any other way is most welcome guys . thanks