# DocumentWriter A type that writes a document’s content to a file. ``` protocol DocumentWriter ``` ## Overview SwiftUI calls your document’s [`snapshot(contentType:)`](/documentation/SwiftUI/WritableDocument/snapshot(contentType:)) on the main actor to capture the current state, then obtains a `DocumentWriter` from [`writer(configuration:)`](/documentation/SwiftUI/WritableDocument/writer(configuration:)) and invokes `write(content:to:previous:progress:)` in the background with coordinated file access. Use [`FileWrapperDocumentWriter`](/documentation/SwiftUI/FileWrapperDocumentWriter) for cases cases that don’t require custom file write logic. Implement a `DocumentWriter` when you need direct URL access or streaming writes: ``` struct ImageWriter: DocumentWriter { @concurrent func write(content image: sending CGImage, to destination: URL, previous: sending CGImage?, progress: consuming Subprogress ) async throws { guard let imageDestination = CGImageDestinationCreateWithURL( destination as CFURL, UTType.jpeg.identifier as CFString, 1, nil ) else { throw CocoaError(.fileWriteUnknown) } CGImageDestinationAddImage( imageDestination, image, nil ) guard CGImageDestinationFinalize( imageDestination ) else { throw CocoaError(.fileWriteUnknown) } } } ``` ## Topics ### Writing a document [`write(snapshot:to:previous:progress:)`](/documentation/SwiftUI/DocumentWriter/write(snapshot:to:previous:progress:)) Writes the document content to disk. [`Snapshot`](/documentation/SwiftUI/DocumentWriter/Snapshot) The type representing the document’s content to write. [`Destination`](/documentation/SwiftUI/DocumentWriter/Destination) The type of the destination location to write to. --- 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)