在iOS12下使用Replaykit时，新增了Broadcast Upload Extension，并且设置了正确的preferredExtension，但是那个唤起的界面始终没有我设置的Extention.
找了两天，各种搜索，最终在Stack Overflow中一条无人赞的评论发现了问题所在！
If your app extension is not visible in PickerView as well as in Control Center, it means that the extension is not installed. Check out the deployment Info in the general section of the Xcode project's target. In my case, I had the same experience when the iOS version of the device was lower than the deployment target version.
在此记录一下，防止有人遇到相同的问题浪费时间。
