Instance Method


This method should be implemented in subclasses that want to validate user changes to a string in a field, where the user changes are not necessarily at the end of the string, and preserve the selection (or set a different one, such as selecting the erroneous part of the string the user has typed).


func isPartialStringValid(_ partialStringPtr: AutoreleasingUnsafeMutablePointer<NSString>, proposedSelectedRange proposedSelRangePtr: NSRangePointer?, originalString origString: String, originalSelectedRange origSelRange: NSRange, errorDescription error: AutoreleasingUnsafeMutablePointer<NSString?>?) -> Bool



The new string to validate.


The selection range that will be used if the string is accepted or replaced.


The original string, before the proposed change.


The selection range over which the change is to take place.

If the user change is a deletion, origSelRange contains the range of the deleted characters.


If non-nil, if validation fails contains an NSString object that describes the problem.

Return Value

true if partialStringPtr is acceptable, otherwise false.


In a subclass implementation, evaluate partialString according to the context. Return true if partialStringPtr is acceptable and false if partialStringPtr is unacceptable. If you return false and assign a new string to partialStringPtr and a new range to proposedSelRangePtr, the string and selection range are changed, otherwise, if no values are assigned to partialStringPtr or proposedSelRangePtr, the change is rejected. If you return false, you can also return by indirection an NSString object (in error) that explains the reason why the validation failed; the delegate (if any) of the NSControl object managing the cell can then respond to the failure in control:didFailToValidatePartialString:errorDescription:.