Smartphone apps shouldn't be used, or cited to build a proper answer or question.
Smart phone apps shouldn't be cited on scientific stacks. Even if they are knowledge databases of some kind, we need more proper sources than that. Personally I dislike even wikipedia as a source for the premise of an answer (or question), as the content is volatile, subject to change, stacked with circle referencing (A can be explained by B - link to B says that B can be explained by A) and indeed often outright incorrect. It's fine to use it as a link to highlight a term and use it for background purposes, but to use wilkipedia as a source to build your answer on, I would say no. Likewise, smartphone apps can be build by anyone, and stuffed with nonsense matter, which is not regulated, controlled, or reviewed in any way.