We've spent the past 5 months rebuilding our mobile apps with Google Flutter enabling us to replace our two codebases (ObjectiveC and Java) with a single codebase.
Here's the code on GitHub:
https://github.com/invoiceninja/flutter-mobile
I've also written about some of our experiences on my blog:
https://hillelcoren.com/2018/05/18/flutter-is-darts-killer-a...
If you have any questions let me know.