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# willPopUpNotification

Posted when an `NSPopUpButton` object receives a mouse-down event—that is, when the user is about to select an item from the menu.

```
class let willPopUpNotification: NSNotification.Name
```

## Discussion

The notification object is the selected `NSPopUpButton` object. This notification does not contain a `userInfo` dictionary.

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

---

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