This is a profoundly stupid decision by Apple. James Thomson, PCalc’s developer, was apparently told that “Notification Center widgets on iOS cannot perform any calculations, and the current PCalc widget must be removed.” That, despite Apple’s own app review guidelines and extension programming guide (PDF) making no mention of this restriction. The App Store editorial team must not be aware of this rule, because PCalc is currently featured as an example of iOS 8’s extensible Notification Centre feature — this is what inspired my use of the word “profound” above.
It’s not the rules themselves that are necessarily a burden on app developers. It’s Apple’s store, so they get to set the rules. But it’s seemingly-arbitrary stuff like this that makes developers lose sleep at night. Thomson clearly spent a great deal of time and care building this extension, and now that’s gone to waste with unfortunately characteristic indifference from Apple. And it’s not like PCalc was rejected outright — Apple allowed it in the store for the past month and a half before pulling it for violating a rule that doesn’t even exist.
It can’t be that Apple doesn’t want interaction in widgets — Strava’s widget allows you to start and stop a session. It can’t even be that calculations aren’t allowed, unless it only pertains to iOS for inexplicable reasons, as Yosemite includes a calculator in its default Today widget bundle. If it’s either of these things, Apple ought to better explain their expectations before developers waste hours doing stuff that’s allowed, only to be summarily rejected for new and unwritten rules.