The short answer is: Parcelable implementations are overly complicated and brittle, I’m bad at finding and fixing “Unmarshalling unknown type code” errors and I’m tired of being surprised by them.
There are hundreds of questions about Parcelable errors on StackOverflow. I’ve had my fill of trying to implement solutions (e.g. proguard configuration adjustments, read/write out of order, etc) and then hoping that the errors stop happening.
If my app runs in a single process and I want to pass some arbitrary custom object to an Activity or Fragment, I’ll create a singleton and store the object as a property on that singleton. Then my Activity or Fragment can get that custom object by calling a “get” method on the singleton. (Of course, it’s important to keep that singleton from holding on to excessive amounts of memory.)
Anyway, the official documentation apparently says we should avoid using Parcelable unless we have to pass an object instance to another process.