如何在DragTarget内部重置值？

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: MyDragTarget(),
      ),
    );
  }
}

class MyDragTarget extends StatefulWidget {
  @override
  _MyDragTargetState createState() => _MyDragTargetState();
}

class _MyDragTargetState extends State<MyDragTarget> {
  String value = '';

  void resetValue() {
    setState(() {
      value = '';
    });
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        Container(
          height: 200,
          width: 200,
          color: Colors.grey,
          child: DragTarget(
            onWillAccept: (data) {
              resetValue(); // 在拖动进入时重置值
              return true;
            },
            onAccept: (data) {
              setState(() {
                value = data; // 更新值
              });
            },
            builder: (context, candidateData, rejectedData) {
              return Center(
                child: Text(
                  value,
                  style: TextStyle(fontSize: 20),
                ),
              );
            },
          ),
        ),
        Draggable(
          data: 'New Value',
          child: Container(
            height: 50,
            width: 100,
            color: Colors.blue,
            child: Center(
              child: Text(
                'Drag Me',
                style: TextStyle(color: Colors.white),
              ),
            ),
          ),
          feedback: Container(
            height: 50,
            width: 100,
            color: Colors.blue.withOpacity(0.5),
            child: Center(
              child: Text(
                'Drag Me',
                style: TextStyle(color: Colors.white),
              ),
            ),
          ),
        ),
      ],
    );
  }
}