如何防止堆栈中的可拖动小部件(使用Matrix4转换创建)在添加另一个可拖动小部件时改变其位置？

import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';
import 'package:vector_math/vector_math_64.dart' show Vector3;

class DraggableWidget extends StatefulWidget {
  @override
  _DraggableWidgetState createState() => _DraggableWidgetState();
}

class _DraggableWidgetState extends State<DraggableWidget> {
  Matrix4 _transform = Matrix4.identity();
  Offset _startPosition;

  @override
  Widget build(BuildContext context) {
    return GestureDetector(
      onPanStart: (details) {
        _startPosition = details.globalPosition;
      },
      onPanUpdate: (details) {
        final currentPosition = details.globalPosition;
        final delta = currentPosition - _startPosition;
        setState(() {
          _transform = Matrix4.translationValues(delta.dx, delta.dy, 0);
        });
      },
      onPanEnd: (_) {
        _startPosition = null;
        // You can save the final position here if needed.
      },
      child: Transform(
        transform: _transform,
        child: Container(
          width: 100,
          height: 100,
          color: Colors.blue,
        ),
      ),
    );
  }
}

class MyHomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Draggable Widget'),
      ),
      body: Stack(
        children: [
          Positioned(
            top: 100,
            left: 100,
            child: DraggableWidget(),
          ),
          // Add more draggable widgets here.
        ],
      ),
    );
  }
}

void main() {
  runApp(MaterialApp(home: MyHomePage()));
}