Building a Native Bluetooth Pairing Sheet with AccessorySetupKit

Activate a session and show the picker

Hold one ASAccessorySession, subscribe to events, then present the picker. ASDiscoveryDescriptor decides "what to show," and ASPickerDisplayItem decides "how it looks."

import AccessorySetupKit
import CoreBluetooth
 
@MainActor
final class AccessoryManager: ObservableObject {
    private let session = ASAccessorySession()
    @Published var current: ASAccessory?
 
    func activate() {
        session.activate(on: .main) { [weak self] event in
            self?.handle(event)
        }
    }
 
    func showPicker() {
        let descriptor = ASDiscoveryDescriptor()
        descriptor.bluetoothServiceUUID = CBUUID(string: "FE2C")
        // Narrow by a name substring to keep unrelated nearby devices out
        descriptor.bluetoothNameSubstring = "MyDevice"
 
        let item = ASPickerDisplayItem(
            name: "My Device",
            productImage: UIImage(named: "device-thumb")!,
            descriptor: descriptor
        )
 
        session.showPicker(for: [item]) { error in
            if let error { print("picker failed: \(error)") }
        }
    }
}

Adding bluetoothNameSubstring filters out unrelated devices advertising the same service. When similar devices crowd the area, a sheet without it gets hard to choose from, so I recommend narrowing by at least part of the name when you can.

Handle events and connect

The closure you pass to activate(on:) receives picker results and device state as events. Branch by type.

When a device is added

When the user picks and approves a device, .accessoryAdded arrives. Save the identifier of the received ASAccessory and, if needed, proceed to a CoreBluetooth connection.

When renamed or removed

Users can rename a device or unpair it from system settings. Handle .accessoryChanged and .accessoryRemoved and always keep your saved state in sync. Ignore this and a device the user "removed" lingers inside your app as an inconsistency.

On failure or cancel

.activated signals the session is ready. If the user closes the sheet, treat it as a plain cancel rather than an error, and just leave a path to re-present. Returning a cancel as a red error alert hurts the experience, so avoid it.

private func handle(_ event: ASAccessoryEvent) {
    switch event.eventType {
    case .accessoryAdded:
        current = event.accessory
        // OK to connect via CoreBluetooth from here
    case .accessoryChanged:
        current = event.accessory
    case .accessoryRemoved:
        current = nil
    default:
        break
    }
}

How to bridge into CoreBluetooth

AccessorySetupKit only settles "which device you may use." The actual data exchange still happens over CoreBluetooth. The difference is that for an authorized device, CoreBluetooth connects without the broad permission dialog.

An ASAccessory carries the Bluetooth identifier, so you reclaim the device with CBCentralManager.retrievePeripherals(withIdentifiers:) and connect. No need to scan again. Reclaiming the single authorized device by name also cuts the steps to a connection.

Where people trip up

The first trap is a mismatch between the Info.plist service UUID and the code's bluetoothServiceUUID. Fix only one and the sheet is silently empty, with a hard-to-trace cause. Before shipping to production, always confirm on a real device that the sheet picks up the device once.

Next, the simulator has no Bluetooth, so AccessorySetupKit testing requires a real device. Before you have the target in hand, lock down the UUID and name declarations first, then verify the picker on a device once one is available.

Finally, dropping removal events. If the user unpairs from system settings and your app does not follow, you get the worst inconsistency: "shows connected but will not connect." Write the cleanup in .accessoryRemoved with the same care you give the connection itself.

Start by putting one service UUID of your device into Info.plist and confirming on a real device that showPicker picks it up. Once that passes, the rest is just adding the connection and the cleanup.