Package “Android Emulator” with revision at least 28.1.9 not available
問題困擾了好幾天，最後google到了答案，這裏貼出來。
https://medium.com/code-procedure-and-rants/android-emulator-q-preview-f80a3568a276
This happens because Android Q is still in beta and therefore it’s only be available through the Canary and Development channels. This makes sense, since it’s on the development stage and we can still have changes between versions. The emulator images seem to follow the same reasoning and with this, for now, you need to download it through these channels.
With this in mind, we’ve got some workarounds on how to install it.
翻譯的大致意思是，Android Q目前處於Beta階段，使用stable版本的SdkManager或者AndroidStudio不能下載到beta版本的東西。相當於不在一個頻道上。所以，你需要下載其他版本的sdkmanager或者AndroidStudio。
方法1，
下載Android Studio 3.5，然後再最新版本中下載新sdk。
The easiest way here is to download and install Android Studio 3.5. Don’t worry, you can have them both installed at the same time. Moreover, it’s easier to distinguish them both, since the Canary’s icon is yellow and the Stable version green.
You can download this version from the official channel.
這裏下載新版本的3.5，使用最新版，下載和管理sdk和AVD。
方法2，
1，改變sdkmanager 頻道
sdkmanager -update -channel=3
- 0-stable
- 1-beta
- 2-developer
- 3-canary
2，Android Studio → Preferences-->Appearance & Behaviour → System Settings → Updates
從stable修改到Canary。然後就可以升級sdk和emulator了。