When comparing Codename One vs ASP.NET Core, the Slant community recommends ASP.NET Core for most people. In the question“What are the best free cross-platform (mobile and desktop no web) app development frameworks that can be used to create commercial apps?” ASP.NET Core is ranked 4th while Codename One is ranked 6th.
Ranked in these QuestionsQuestion Ranking
Pro High performance
Pro Open source
Pro Highly customizable
By utilizing lightweight component architecture and the built in graphical designer and theming options you are able to customize a good looking app on any platform.
Pro Java 8 support
Pro Works with all IDEs
Works with NetBeans, Eclipse, IntelliJ, etc.
Pro Multi-platform development environments (via build server)
You can even use Linux desktops to build native iOS apps, no need for a Mac.
Pro Vibrant & helpful community
Pro Attractive pricing
It is possible to build production grade apps even with the free version. Pricing is decent when compared to competitors like Xamarin.
Pro Fast and getting faster
Pro Built-in middleware
Pro Multi Platform
Can run on Windows, Linux and Mac (also Visual Studio Code editor).
Ability to host on IIS, Nginx, Apache, Docker, or self-host in your own process.