Transfer app data to or from other platforms using AppMigrationKit. Use when implementing system-orchestrated one-time migration between iOS and Android or another platform, building an AppMigrationExtension, packaging transportable resources with ResourcesArchiver, importing resources on the destination device, reporting import progress, handling migration errors and app group cleanup, checking MigrationStatus, or testing migration code with AppMigrationTester.
SKILL.md
AppMigrationKit
One-time cross-platform data transfer for app resources. Enables apps to
export data to or import data from another platform (for example, Android)
during device setup or onboarding. AppMigrationKit APIs are iOS 26.0+ /
iPadOS 26.0+; the data-container entitlement is iOS 26.1+ / iPadOS 26.1+ /
Mac Catalyst 26.1+. Swift 6.3.
Beta-sensitive. AppMigrationKit is new in iOS 26 and may change before GM.
Re-check current Apple documentation before relying on specific API details.
AppMigrationKit uses an app extension model. The system orchestrates the
transfer between devices. The app provides an extension conforming to export
and import protocols, and the system calls that extension at the appropriate
time. The app itself never manages the network connection between devices.
App extension -- An AppMigrationExtension conforming type that the
system invokes during migration. It handles data export and import.
Installs
0
System orchestration -- The OS manages the device-to-device session,
transport, and scheduling. The extension does not control when it runs.
Containing app -- After migration completes, the app checks
MigrationStatus.importStatus on first launch to determine whether
migration occurred and whether it succeeded.
Key types:
Type
Role
AppMigrationExtension
Protocol for the app extension entry point
ResourcesExportingWithOptions
Protocol for exporting files via archiver
ResourcesExporting
Simplified export protocol (no custom options)
ResourcesImporting
Protocol for importing files on the destination
ResourcesArchiver
Streams files into the export archive
MigrationDataContainer
Access to the containing app's data directories
MigrationStatus
Check import result from the containing app
MigrationPlatform
Identifies the other device's platform (e.g., .android)
MigrationAppIdentifier
Identifies the source app by store and bundle ID
AppMigrationTester
Test-only actor for validating export/import logic
Setup and Entitlements
Entitlement
The app extension requires the com.apple.developer.app-migration.data-container-access
entitlement. Its value is a single-element string array containing the bundle
identifier of the containing app:
No other values are valid. This entitlement grants the extension read access
to the containing app's data container during export and write access during
import. The entitlement itself is available on iOS 26.1+, iPadOS 26.1+,
and Mac Catalyst 26.1+, even though the core AppMigrationKit APIs are
available on iOS 26.0+ and iPadOS 26.0+.
Extension Target
Add a new App Extension target to the Xcode project. The extension conforms
to one or more of the migration protocols (ResourcesExportingWithOptions,
ResourcesExporting, ResourcesImporting).
App Migration Extension
The extension entry point conforms to AppMigrationExtension. During
migration, the system prevents launching the containing app and its other
extensions to ensure exclusive data access.
Accessing the Data Container
The extension accesses the containing app's files through appContainer:
import AppMigrationKit
struct MyMigrationExtension: ResourcesExporting {
var resourcesSizeEstimate: Int { estimateTotalExportSize() }
var resourcesVersion: String { "1.0" }
var resourcesCompressible: Bool { true }
func exportResources(
to archiver: sending ResourcesArchiver,
request: MigrationRequest
) async throws {
let container = appContainer
// container.bundleIdentifier -- app's bundle ID
// container.containerRootDirectory -- root of the app container
// container.documentsDirectory -- Documents/
// container.applicationSupportDirectory -- Application Support/
}
}
MigrationDataContainer provides containerRootDirectory, documentsDirectory,
and applicationSupportDirectory as URL values pointing into the containing
app's sandbox.
Exporting Resources
Conform to ResourcesExportingWithOptions (or ResourcesExporting for no
custom options) to package files for transfer. The system calls
exportResources(to:request:) with a ResourcesArchiver and a
MigrationRequestWithOptions.
Declaring Export Properties
struct MyMigrationExtension: ResourcesExportingWithOptions {
typealias OptionsType = MigrationDefaultSupportedOptions
var resourcesSizeEstimate: Int {
// Return estimated total bytes of exported data
calculateExportSize()
}
var resourcesVersion: String {
"1.0"
}
var resourcesCompressible: Bool {
true // Let the system compress during transport
}
}
resourcesSizeEstimate -- Estimated total bytes. The system uses this for
progress UI and free-space checks.
resourcesVersion -- Format version string. The import side receives this
to handle versioned data formats.
resourcesCompressible -- When true, the archiver may compress files
during transport.
Implementing Export
func exportResources(
to archiver: sending ResourcesArchiver,
request: MigrationRequestWithOptions<MigrationDefaultSupportedOptions>
) async throws {
let docsDir = appContainer.documentsDirectory
// Check destination platform if needed
if request.destinationPlatform == .android {
// Platform-specific export logic
}
// Append files one at a time -- make continuous progress
let userDataURL = docsDir.appending(path: "user_data.json")
try await archiver.appendItem(at: userDataURL)
// Append with a custom archive path
let settingsURL = docsDir.appending(path: "settings.plist")
try await archiver.appendItem(at: settingsURL, pathInArchive: "preferences/settings.plist")
// Append a directory
let photosDir = docsDir.appending(path: "photos")
try await archiver.appendItem(at: photosDir, pathInArchive: "media/photos")
}
The archiver streams files incrementally. Call appendItem(at:pathInArchive:)
repeatedly as each resource is ready. The system may terminate the extension
if it appears hung, so avoid long gaps between append calls.
Cancellation
ResourcesArchiver handles task cancellation automatically by throwing
cancellation errors. Do not catch these errors -- doing so causes the system
to kill the extension.
Migration Platform
MigrationRequestWithOptions exposes destinationPlatform as a
MigrationPlatform value. Use this to tailor exported data:
if request.destinationPlatform == .android {
// Export in a format the Android app expects
}
MigrationPlatform provides .android as a static constant. Custom
platforms can be created with MigrationPlatform("customPlatform").
Importing Resources
Conform to ResourcesImporting to receive transferred files on the
destination device. The system calls importResources(at:request:) after
app installation but before the app is launchable.
struct MyMigrationExtension: ResourcesImporting {
func importResources(
at importedDataURL: URL,
request: ResourcesImportRequest
) async throws {
let sourceVersion = request.sourceVersion
let sourceApp = request.sourceAppIdentifier
// sourceApp.platform -- e.g., .android
// sourceApp.bundleIdentifier -- source app's bundle ID
// sourceApp.storeIdentifier -- e.g., .googlePlay
// Copy imported files into the app container
let docsDir = appContainer.documentsDirectory
let userData = importedDataURL.appending(path: "user_data.json")
if FileManager.default.fileExists(atPath: userData.path()) {
try FileManager.default.copyItem(
at: userData,
to: docsDir.appending(path: "user_data.json")
)
}
}
}
Error Handling During Import
On import error, the system clears the containing app's data container to
prevent partial state. However, app group containers are not cleared. The
import implementation should clear any app group containers before writing
imported content:
func importResources(
at importedDataURL: URL,
request: ResourcesImportRequest
) async throws {
// Clear shared app group data first
let groupURL = FileManager.default.containerURL(
forSecurityApplicationGroupIdentifier: "group.com.example.myapp"
)
if let groupURL {
try? FileManager.default.removeItem(at: groupURL.appending(path: "shared_data"))
}
// Then import
try await performImport(from: importedDataURL)
}
Source App Identifier
ResourcesImportRequest provides sourceAppIdentifier as a
MigrationAppIdentifier with three properties:
platform -- The source device's platform (e.g., .android)
bundleIdentifier -- The source app's bundle identifier
storeIdentifier -- The app store (e.g., .googlePlay)
Migration Status
After migration completes, the containing app checks the result on first
launch:
import AppMigrationKit
func application(
_ application: UIApplication,
didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
) -> Bool {
if let status = MigrationStatus.importStatus {
switch status {
case .success:
showMigrationSuccessUI()
MigrationStatus.clearImportStatus()
case .failure(let error):
showMigrationFailureUI(error: error)
MigrationStatus.clearImportStatus()
}
}
return true
}
MigrationStatus.importStatus is nil if no migration occurred.
Call clearImportStatus() after handling the result to prevent showing
the notification on subsequent launches.
The enum has two cases: .success and .failure(any Error).
Progress Tracking
The import side exposes a Progress object via resourcesImportProgress.
The system uses this to display transfer progress to the user. Update
completedUnitCount incrementally during import:
struct MyMigrationExtension: ResourcesImporting {
private let importProgress = Progress(totalUnitCount: 100)
var resourcesImportProgress: Progress { importProgress }
func importResources(
at importedDataURL: URL,
request: ResourcesImportRequest
) async throws {
let files = try FileManager.default.contentsOfDirectory(
at: importedDataURL, includingPropertiesForKeys: nil
)
let increment = Int64(100 / max(files.count, 1))
for file in files {
try processFile(file)
importProgress.completedUnitCount += increment
}
importProgress.completedUnitCount = 100
}
}
Testing
AppMigrationTester is a test-only actor for validating migration logic
in unit tests hosted by the containing app. Do not use it in production.
DON'T: Catch cancellation errors from ResourcesArchiver
// WRONG -- system kills the extension if cancellation is swallowed
func exportResources(to archiver: sending ResourcesArchiver, request: ...) async throws {
do {
try await archiver.appendItem(at: fileURL)
} catch is CancellationError {
// Swallowing this causes termination
}
}
// CORRECT -- let cancellation propagate
func exportResources(to archiver: sending ResourcesArchiver, request: ...) async throws {
try await archiver.appendItem(at: fileURL)
}
DON'T: Leave long gaps between archiver append calls
// WRONG -- system may assume the extension is hung and terminate it
func exportResources(to archiver: sending ResourcesArchiver, request: ...) async throws {
let allFiles = gatherAllFiles() // Takes 30 seconds
for file in allFiles {
try await archiver.appendItem(at: file)
}
}
// CORRECT -- interleave file preparation with archiving
func exportResources(to archiver: sending ResourcesArchiver, request: ...) async throws {
for file in knownFilePaths() {
try await archiver.appendItem(at: file)
}
}
DON'T: Convert files to intermediate format during export
// WRONG -- may exhaust disk space creating temporary copies
func exportResources(to archiver: sending ResourcesArchiver, request: ...) async throws {
let converted = try convertToJSON(originalDatabase) // Doubles disk usage
try await archiver.appendItem(at: converted)
}
// CORRECT -- export files as-is, convert on import side if needed
func exportResources(to archiver: sending ResourcesArchiver, request: ...) async throws {
try await archiver.appendItem(at: originalDatabase)
}
DON'T: Ignore app group containers during import error recovery
// WRONG -- system clears app container but not app groups on error
func importResources(at url: URL, request: ResourcesImportRequest) async throws {
try writeToAppGroup(data)
try writeToAppContainer(data) // If this throws, app group has stale data
}
// CORRECT -- clear app group data before importing
func importResources(at url: URL, request: ResourcesImportRequest) async throws {
try clearAppGroupData()
try writeToAppGroup(data)
try writeToAppContainer(data)
}
DON'T: Forget to clear import status after handling it
// WRONG -- migration UI shows every launch
if let status = MigrationStatus.importStatus {
showMigrationResult(status)
// Missing clearImportStatus()
}
// CORRECT
if let status = MigrationStatus.importStatus {
showMigrationResult(status)
MigrationStatus.clearImportStatus()
}
Review Checklist
Extension target added with com.apple.developer.app-migration.data-container-access entitlement
Entitlement array contains exactly one string: the containing app's bundle identifier
Extension conforms to ResourcesExportingWithOptions or ResourcesExporting for export
Extension conforms to ResourcesImporting for import
resourcesSizeEstimate returns a reasonable byte estimate
resourcesVersion is set and will be checked on import for format compatibility
Export calls appendItem incrementally without long pauses
Cancellation errors from ResourcesArchiver are not caught
Import clears app group containers before writing new data
Containing app checks MigrationStatus.importStatus on first launch
clearImportStatus() called after handling the migration result
AppMigrationTester used in unit tests to validate export and import
Files are exported as-is without intermediate format conversion on the export side
sourceVersion from import request used to handle versioned data formats
