问题
Earlier today I had an issue where controls weren't rendering in the layout designer (see here) - I managed to fix this by setting the target framework of the app to 8.0 to match the version set at the top of the designer.
Problem is I need the target framework to be 9.0 and I only have 8.0 available in the designer. How do you add versions here? I have 9.0 installed in Tools/Android/Android SDK Manager/Platforms.
Any help would be appreciated.
来源：https://stackoverflow.com/questions/55186949/xamarin-android-adding-versions-to-the-layout-designer