有没有办法检查Flutter video-player包中的VideoPlayerController是否已经被释放？

import 'package:flutter/material.dart';
import 'package:video_player/video_player.dart';

class VideoPlayerScreen extends StatefulWidget {
  @override
  _VideoPlayerScreenState createState() => _VideoPlayerScreenState();
}

class _VideoPlayerScreenState extends State<VideoPlayerScreen> {
  VideoPlayerController _controller;

  @override
  void initState() {
    super.initState();
    _controller = VideoPlayerController.network('https://example.com/video.mp4');
    _controller.initialize().then((_) {
      setState(() {});
    });
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    if (_controller.value == null) {
      // VideoPlayerController已经被释放
      return Text('VideoPlayerController已经被释放');
    }

    if (!_controller.value.isInitialized) {
      // VideoPlayerController正在初始化
      return CircularProgressIndicator();
    }

    return AspectRatio(
      aspectRatio: _controller.value.aspectRatio,
      child: VideoPlayer(_controller),
    );
  }
}