An opensource app showcasing Flutter components, with side-by-side source code view. Source code: Click on list items of home page to see demos of different Flutter components, the source code is just besides the previews!; ).
X.WEI is the official developer of Flutter Catalog with source code side-by-side that can be found in the Libraries & Demo category. The most recent update was on Nov 5, 2019 and the tool was downloaded and set up by over 10K users. According to the latest info, this application is rated 5 on Google Play.