 		}
 	}
 
-	override class func cellClass() -> AnyClass? {
+	override public class func cellClass() -> AnyClass? {
 		return ZDComboBoxCell.self
 	}
 

		self.addSubview(dropDownButton!)
	}

	override func resizeSubviewsWithOldSize(oldSize: NSSize) {
		// need to move button if frame of a control changed
		let buttonHeight = frame.size.height
		let buttonWidth = buttonHeight*ZDComboBoxCell.buttonAspect

		}
	}

	override public func setValue(value: AnyObject?, forKey key: String) {
		switch(key) {
		case "displayKey":
			if let string = value as? String {
