# fileWrapper(snapshot:configuration:) Serializes a document snapshot to a file wrapper. ``` func fileWrapper(snapshot: Self.Snapshot, configuration: Self.WriteConfiguration) throws -> FileWrapper ``` ## Parameters `snapshot` The document snapshot to save. `configuration` Information about a file that already exists for the document, if any. ## Return Value The destination to serialize the document contents to. The value can be a newly created or an update of the one provided in the `configuration` input. ## Discussion To store a document — for example, in response to a Save command — SwiftUI begins by calling the [`snapshot(contentType:)`](/documentation/SwiftUI/ReferenceFileDocument/snapshot(contentType:)) method to get a copy of the document data in its current state. Then SwiftUI passes that snapshot to this method, where you serialize it and create or modify a file wrapper with the serialized data: ``` func fileWrapper(snapshot: Snapshot, configuration: WriteConfiguration) throws -> FileWrapper { let data = try JSONEncoder().encode(snapshot) return FileWrapper(regularFileWithContents: data) } ``` SwiftUI disables document edits during the snapshot to ensure that the document’s data remains coherent, but reenables edits during the serialization operation. > Note: SwiftUI calls this method on a background thread. Don’t > make user interface changes from that thread. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)