We have the same philosophy. Most of my experience here is with iOS and Android, but also a bit of Windows/Linux/Mac. If it's going to feel polished, then it's going to need a separate UI front-end for each platform.
It's not that there's not yet a sufficiently good cross-platform library; it's that an Android app and an iOS app are different! They're structured differently! And if you try to use an x-platform library, you're going to end up with an iOS-app-that-runs-on-Android, or an Android-app-that-runs-on-iOS, or a this-app-doesn't-feel-right-anywhere.
My approach varies based on the application, but in general one of two things end up happening: either the majority of the processing gets pushed onto a server with a well-defined REST API, or the processing gets put in a C++ library that gets linked everywhere (with JNI shims, ctypes shims, whatever's needed to load it in the appropriate environment).
This approach does a few things: it ensures that you've got a UI that fits every platform, it improves code quality (you can't add a chunk of business logic in your view handler), and it makes porting so much easier.
It's not that there's not yet a sufficiently good cross-platform library; it's that an Android app and an iOS app are different! They're structured differently! And if you try to use an x-platform library, you're going to end up with an iOS-app-that-runs-on-Android, or an Android-app-that-runs-on-iOS, or a this-app-doesn't-feel-right-anywhere.
My approach varies based on the application, but in general one of two things end up happening: either the majority of the processing gets pushed onto a server with a well-defined REST API, or the processing gets put in a C++ library that gets linked everywhere (with JNI shims, ctypes shims, whatever's needed to load it in the appropriate environment).
This approach does a few things: it ensures that you've got a UI that fits every platform, it improves code quality (you can't add a chunk of business logic in your view handler), and it makes porting so much easier.