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# willResizeSubviewsNotification

A notification that posts before a change to the size of some or all subviews of a split view.

```
class let willResizeSubviewsNotification: NSNotification.Name
```

## Discussion

The notification object consists of the [`NSSplitView`](/documentation/AppKit/NSSplitView) object about to resize its subviews.

The <doc://com.apple.documentation/documentation/Foundation/Notification/userInfo> dictionary includes the `NSSplitViewDividerIndex` key that contains the index of the divider that the split view or the user moves. If the system sends the notification because the user drags a divider, the dictionary also includes the `NSSplitViewUserResizeKey` key with a value of `1`.

To observe this notification using Swift concurrency, use [`NSSplitView.WillResizeSubviewsMessage`](/documentation/AppKit/NSSplitView/WillResizeSubviewsMessage).

---

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