The system share sheet is the standard exit to other apps

What it is

The system share sheet is the OS-provided exit that hands the current payload to another app. The sender declares that something is shareable; it does not enumerate every installed app or open the receiver's composer itself. The OS assembles destinations from registered receivers, recents, and pinned items, then delivers after the person picks one. In-app "send to a friend" follows the product's social graph. The sheet follows the device's cross-app graph. This entry is about that exit role. It is not about why a homemade icon row misses targets, and not about which payload format the receiver can actually open.

Why it happens

Sandboxing blocks a sender from seeing the full install list or invoking arbitrary write entry points. The sheet is a system broker: the sender registers content, the OS matches extensions or intent filters that claimed they accept that kind of thing, and the chosen receiver is wired up. Recents and pins are the OS's memory of this device's sharing graph, not the sender's contact list, so the same button expands to different targets on different phones. The cost of a standard exit is that the sender loses control of the destination UI. What happens after delivery is a contract between the receiver and the OS, not a step in the sender's navigation stack.

Where it stops holding

Closed devices with no third-party receivers (some feature phones, managed terminals with an allowlist) may show an empty sheet or only "Save to Files"; in-app send remains the only path. Intra-enterprise handoff that never leaves a logged-in product (expense submit, ticket transfer) is not a device-level share and should not be forced through the sheet. On desktop the equivalents are drag-and-drop and the clipboard, not a card sliding up from the bottom edge. Saving inside the current app (favorites, add to album) is an in-app action, not a cross-app exit.

Applying it

• Route any "continue this in another app" action to the system share sheet, rather than opening only the product's own friend picker.
• Have the sender hand over the payload and a readable preview title; do not insert a "pick a platform" page before the sheet.
• Verify by installing a notes or files app the product has never integrated with. Sharing from the product should list that app and complete delivery with no extra row added in product code.

Related

• Within the group: K1.07.2 Homegrown share lists miss the destinations people already use · K1.07.3 Share payload format determines whether the receiver can use it
• Adjacent: K2.05 Cross-application drag and drop · K2.10 Clipboard and system services
• Search terms: share sheet · UIActivityViewController · Android Sharesheet