网上下了一个基于Xamarin开发的安卓应用源码项目，当我修改代码等检查都没有问题后就开始存档，但每次存档VS2017总是跳出失败，提示“请先确保存档前先生成项目”我就很纳闷。
这是错误代码
2>------ 已启动生成: 项目: PlayTube.Android, 配置: Debug Any CPU ------
2>D:\playtube-mobile-application\PlayTube_v1.1\packages\Microsoft.Bcl.Build.1.0.14\tools\Microsoft.Bcl.Build.targets(225,5): warning : All projects referencing PlayTube.csproj must install nuget package Microsoft.Bcl.Build. For more information, see http://go.microsoft.com/fwlink/?LinkID=317569.
2>D:\Program Files (x86)\Microsoft Visual Studio\2017\Community\MSBuild\15.0\Bin\Microsoft.Common.CurrentVersion.targets(2110,5): warning MSB3277: 发现“Microsoft.CSharp”的不同版本间存在无法解决的冲突。当日志详细信息设置为“详细”时，这些引用冲突将会在生成日志中列出。
2>D:\playtube-mobile-application\PlayTube_v1.1\packages\Xamarin.Build.Download.0.4.7\build\Xamarin.Build.Download.targets(62,3): error XBD009: Partial Download Failed for one or more parts
2>D:\playtube-mobile-application\PlayTube_v1.1\packages\Xamarin.Build.Download.0.4.7\build\Xamarin.Build.Download.targets(62,3): error : 发送请求时出错。
2>D:\playtube-mobile-application\PlayTube_v1.1\packages\Xamarin.Build.Download.0.4.7\build\Xamarin.Build.Download.targets(62,3): error XBD404: Please open the Android SDK Manager and install the latest version of 'Google Repository' from the 'Extras' section, and then reload your solution.
这是生成解决方案错误提示
