# completedString(_:) Returns a string from the combo box’s pop-up list that starts with the given substring. ``` func completedString(_ string: String) -> String? ``` ## Parameters `string` The substring to search for. This is what the user entered in the combo box’s text field. ## Return Value The string from the combo box’s pop-up list that starts with the specified substring or `nil` if there is no such string. ## Discussion The default implementation of this method first checks whether the combo box uses a data source and whether the data source responds to comboBox:completedString: or comboBoxCell:completedString:. If so, the combo box cell returns that method’s return value. Otherwise, this method goes through the combo box’s items one by one and returns an item that starts with `substring`. Override this method only if your subclass completes strings differently. The overriding method does not need to call the superclass’s method. Generally, you do not need to call this method directly. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)