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# readInBackgroundAndNotify()

Reads from the file or communications channel in the background and posts a notification when finished.

```
func readInBackgroundAndNotify()
```

## Discussion

This method performs an asynchronous [`availableData`](/documentation/Foundation/FileHandle/availableData) operation on a file or communications channel and posts an [`readCompletionNotification`](/documentation/Foundation/FileHandle/readCompletionNotification) notification on the current thread when that operation is complete. You must call this method from a thread that has an active run loop.

The length of the data is limited to the buffer size of the underlying operating system. The notification includes a `userInfo` dictionary that contains the data read; access this object using the `NSFileHandleNotificationDataItem` key.

Any object interested in receiving this data asynchronously must add itself as an observer of [`readCompletionNotification`](/documentation/Foundation/FileHandle/readCompletionNotification). In communication via stream-type sockets, the receiver is often the object returned in the `userInfo` dictionary of [`NSFileHandleConnectionAccepted`](/documentation/Foundation/NSNotification/Name-swift.struct/NSFileHandleConnectionAccepted).

Note that this method does not cause a continuous stream of notifications to be sent. If you wish to keep getting notified, you’ll also need to call [`readInBackgroundAndNotify()`](/documentation/Foundation/FileHandle/readInBackgroundAndNotify()) in your observer method.

## See Also

[`-  enqueueNotification:postingStyle:coalesceMask:forModes:`](/documentation/Foundation/NotificationQueue/enqueue(_:postingStyle:coalesceMask:forModes:))

Adds a notification to the notification queue with a specified posting style, criteria for coalescing, and run loop mode.


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