How do you save a document or blob locally using files?

Short answer

Get an app-specific path through path_provider, then use dart:io to read and write asynchronously while handling disk failures.

Explanation

A file suits cases where the unit you read and write is a document or a binary blob such as an image or an export. Do not assume a fixed path specific to one system; request a directory appropriate to the platform, and consider atomic writes, file size, and permissions. If you need to search inside many fields or relations, the file alone is not a suitable boundary.

Code example

final directory = await getApplicationDocumentsDirectory();
final file = File("${directory.path}/draft.json");
await file.writeAsString(jsonText);

Common mistakes

• Hardcoding a path such as /data or C:\ in shared code.
• Performing a synchronous write on the UI thread for a large file.
• Treating the existence of the file as proof that its content is always valid.

Follow-up questions

• How do you design local persistence that is testable and resilient to storage failure?

Sources

• Flutter cookbook — Read and write files