如何获取颤动中InteractiveViewer的当前标度的值？

import 'package:flutter/material.dart';

class MyInteractiveViewer extends StatefulWidget {
  @override
  _MyInteractiveViewerState createState() => _MyInteractiveViewerState();
}

class _MyInteractiveViewerState extends State<MyInteractiveViewer> {
  TransformationController _controller = TransformationController();

  @override
  Widget build(BuildContext context) {
    return InteractiveViewer(
      transformationController: _controller,
      onInteractionEnd: (details) {
        Matrix4 matrix = _controller.value;
        double scale = matrix.getMaxScaleOnAxis();
        print('当前缩放值：$scale');
      },
      child: Container(
        width: 200,
        height: 200,
        color: Colors.blue,
      ),
    );
  }
}