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# Outline View Button Keys

These keys are used by the outline view to create disclosure buttons that collapse and expand items.

## Discussion

The outline view creates these buttons by calling its inherited [`makeView(withIdentifier:owner:)`](/documentation/AppKit/NSTableView/makeView(withIdentifier:owner:)) method, passing in the key as the identifier and the delegate as the owner.

> Note:
> These keys are backwards compatible to OS X v10.7, however, the symbol is not exported prior to v10.9 and the string value (`@"NSOutlineViewDisclosureButtonKey"`) must be used.

## Topics

### Constants

[`class let disclosureButtonIdentifier: NSUserInterfaceItemIdentifier`](/documentation/AppKit/NSOutlineView/disclosureButtonIdentifier)

The normal triangle disclosure button.

[`class let showHideButtonIdentifier: NSUserInterfaceItemIdentifier`](/documentation/AppKit/NSOutlineView/showHideButtonIdentifier)

The Show/Hide button.


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