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# supportedServiceSources(for:completionHandler:)

Asks the File Provider extension for an array of custom communication channels.

```
func supportedServiceSources(for itemIdentifier: NSFileProviderItemIdentifier, completionHandler: @escaping ([any NSFileProviderServiceSource]?, (any Error)?) -> Void) -> Progress
```

## Parameters

`itemIdentifier`

The item’s identifier.

`completionHandler`

A block that you call after gathering the service sources. You pass the following parameters:

- serviceSources: An array of service sources that lets you communicate with the host app.
- error: If an error occurs, this object contains information about the error; otherwise, it’s `nil`.

## Return Value

An item that tracks the progress of the

## Discussion

The system calls this method when an app requests a list of supported services. Return an array of services for the specified file. An application with access to the file can request the supported services by calling the <doc://com.apple.documentation/documentation/Foundation/FileManager> class’s <doc://com.apple.documentation/documentation/Foundation/FileManager/getFileProviderServicesForItem(at:completionHandler:)> method. For more information, see <doc://com.apple.documentation/documentation/Foundation/NSFileProviderService>.

---

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