# validateValue(_:forKey:) Indicates whether the value specified by a given pointer is valid, or can be made valid, for the property identified by a given key. ``` func validateValue(_ ioValue: AutoreleasingUnsafeMutablePointer, forKey inKey: String) throws ``` ## Parameters `ioValue` A pointer to a new value for the property identified by `inKey`. This method may modify or replace the value in order to make it valid. `inKey` The name of one of the receiver’s properties. The key must specify an attribute or a to-one relationship. ## Discussion In Swift, this method throws an error if the value isn’t valid. In Objective-C, it returns a Boolean value. The default implementation of this function searches the class of the receiver for a property-specific validation function with a particular signature, allowing that function to determine the outcome of the validation. For it to be found, the property-specific validation function must be exposed to Objective-C, must be named according to the pattern `validate`, must take a single, optional `AnyObject` pointer argument, and must throw. For example, for a property named `someString`, the validation function is: ```swift @objc func validateSomeString(_ ioValue: AutoreleasingUnsafeMutablePointer) throws { // Test, and possibly replace the value here; or throw an error } ``` If you define such a function, the default implementation of [`validateValue(_:forKey:)`](/documentation/ObjectiveC/NSObject-swift.class/validateValue(_:forKey:)) calls it when asked to validate the corresponding property, allowing your function to either alter the input value or throw an error. If no such function exists for a particular property, [`validateValue(_:forKey:)`](/documentation/ObjectiveC/NSObject-swift.class/validateValue(_:forKey:))returns [`YES`](/documentation/ObjectiveC/YES) without taking any other action. In other words, by default, the general validation call succeeds if you don’t explicitly provide a validation function for the given property. > Note: > You typically use the validation described here only in Objective-C. In Swift, property validation is more idiomatically handled by relying on compiler support for optionals and strong type checking, while using the built-in `willSet` and `didSet` property observers to test any run-time API contracts, as described in the [Property Observers](https://developer.apple.com/library/archive/documentation/Swift/Conceptual/Swift_Programming_Language/Properties.html#//apple_ref/doc/uid/TP40014097-CH14-ID262) section of [The Swift Programming Language (Swift 4.1)](https://developer.apple.com/library/archive/documentation/Swift/Conceptual/Swift_Programming_Language/index.html#//apple_ref/doc/uid/TP40014097). See [Adding Validation](https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/KeyValueCoding/Validation.html#//apple_ref/doc/uid/20002173) in [Key-Value Coding Programming Guide](https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/KeyValueCoding/index.html#//apple_ref/doc/uid/10000107i) for more information. --- 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)