Unity設置.Net版本為4.6後, IDE失去了智能提示功能. 查看輸出發現錯誤訊息:

The reference assemblies for framework ".NETFramework,Version=v4.6" were not found.

意思是找不到 .Net 4.6的程序集.

只要安裝 .Net 4.6的Targeting Pack就能解決.