---
title: "fileWrapper(snapshot:configuration:)"
framework: swiftui
role: symbol
role_heading: Instance Method
path: "swiftui/referencefiledocument/filewrapper(snapshot:configuration:)"
---

# fileWrapper(snapshot:configuration:)

Serializes a document snapshot to a file wrapper.

## Declaration

```swift
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

Return Value The destination to serialize the document contents to. The value can be a newly created FileWrapper or an update of the one provided in the configuration input.

## Discussion

Discussion To store a document — for example, in response to a Save command — SwiftUI begins by calling the 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.

## See Also

### Writing a document

- [writableContentTypes](swiftui/referencefiledocument/writablecontenttypes.md)
- [ReferenceFileDocument.WriteConfiguration](swiftui/referencefiledocument/writeconfiguration.md)