Shiny.AppFunctions — Siri and Gemini, From One C# Record | Community Feed

Assistants are becoming the front door of the phone, but Apple’s App Intents (Swift) and Google’s Android 16 AppFunctions (Kotlin) have nothing in common — so “let the assistant create an order” normally becomes two features in two languages your app isn’t written in. Allan Ritchie built Shiny.AppFunctions to declare it once in C#.

What you’ll learn

One record, both assistants — an [AppFunction] record with an IAppFunctionHandler becomes a real iOS App Intent (Siri, Spotlight, Shortcuts, Apple Intelligence) and an Android 16 AppFunction for Gemini, same id and handler
No Swift, Kotlin, or plist — a Roslyn source generator emits the Swift intents, AppShortcutsProvider, and Android schema; build targets run swiftc and Apple’s metadata/Siri phrase processors before signing
The “which customer?” problem — one [AppEntity] + IAppEntityQuery gives iOS a native picker and generates a companion search_customer function for Android, which has no picker
Delegates as a gate — auth checks per call, with Deny and iOS’s nicer OpenApp flow, plus context.Platform telling you Siri vs Gemini
A free tool registry — every function exposes GetParametersJsonSchema(), so an in-app chat or MCP server can call the same handlers as a third assistant

Read the full post for the sample orders app, supported types, error mapping, and the compile-time diagnostics that catch a missing handler before deploy.