视频播放器找不到exoplayer,Gradle出错

我是个新手,正在尝试对视频播放器包做一个简单的测试。但是,当我尝试在Android Emulator上运行此设置时;另外,当我在Android设备上运行它(在IOS上运行正常)时,它会失败,并显示以下错误消息:

失败:生成失败,出现异常。 *出了什么问题:

找不到com.google.android.exoplayer:exoplayer核心:2.8.0。

Gradle任务assembleDebug失败,退出代码为1

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

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {

  @override
    Widget build(BuildContext context) {

      return MaterialApp(
        title: 'Video Example',
        home: VideoExample(),
      );
    }
}

class VideoExample extends StatefulWidget {

  VideoState createState() => VideoState();
}

class VideoState extends State<VideoExample> {
 VideoPlayerController playerController;
 VoidCallback listener;

  @override
  void initState() {
    super.initState();
    listener = () {
      setState(() {});
    };
  }

  void createVideo() {
    if (playerController == null) {
      playerController =
          VideoPlayerController.asset('assets/videos/PilatesTestOverview.mp4')
            ..addListener(listener)
            ..setVolume(1.0)
            ..initialize();
    }
  }

@override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Video Example'),
      ),
      body: Center(
        child: AspectRatio(
          aspectRatio: 16 / 9,
          child: Container(
            child: (playerController != null
            ? VideoPlayer(playerController)
            : Container()),
          ),
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          createVideo();
          playerController.play();
        },
        child: Icon(Icons.play_arrow),
      ),
    );
  }
}

和我的Pubsepc.Yaml包依赖项: