# NSKeyValueCoding A mechanism by which you can access the properties of an object indirectly by name or key. ## Discussion The basic methods for accessing an object’s values are [`setValue(_:forKey:)`](/documentation/ObjectiveC/NSObject-swift.class/setValue(_:forKey:)), which sets the value for the property identified by the specified key, and [`value(forKey:)`](/documentation/ObjectiveC/NSObject-swift.class/value(forKey:)), which returns the value for the property identified by the specified key. Thus, all of an object’s properties can be accessed in a consistent manner. The default implementation relies on the accessor methods normally implemented by objects (or to access instance variables directly if need be). ## Topics ### Getting Values [`value(forKey:)`](/documentation/ObjectiveC/NSObject-swift.class/value(forKey:)) Returns the value for the property identified by a given key. [`value(forKeyPath:)`](/documentation/ObjectiveC/NSObject-swift.class/value(forKeyPath:)) Returns the value for the derived property identified by a given key path. [`dictionaryWithValues(forKeys:)`](/documentation/ObjectiveC/NSObject-swift.class/dictionaryWithValues(forKeys:)) Returns a dictionary containing the property values identified by each of the keys in a given array. [`value(forUndefinedKey:)`](/documentation/ObjectiveC/NSObject-swift.class/value(forUndefinedKey:)) Invoked by [`value(forKey:)`](/documentation/ObjectiveC/NSObject-swift.class/value(forKey:)) when it finds no property corresponding to a given key. [`mutableArrayValue(forKey:)`](/documentation/ObjectiveC/NSObject-swift.class/mutableArrayValue(forKey:)) Returns a mutable array proxy that provides read-write access to an ordered to-many relationship specified by a given key. [`mutableArrayValue(forKeyPath:)`](/documentation/ObjectiveC/NSObject-swift.class/mutableArrayValue(forKeyPath:)) Returns a mutable array that provides read-write access to the ordered to-many relationship specified by a given key path. [`mutableSetValue(forKey:)`](/documentation/ObjectiveC/NSObject-swift.class/mutableSetValue(forKey:)) Returns a mutable set proxy that provides read-write access to the unordered to-many relationship specified by a given key. [`mutableSetValue(forKeyPath:)`](/documentation/ObjectiveC/NSObject-swift.class/mutableSetValue(forKeyPath:)) Returns a mutable set that provides read-write access to the unordered to-many relationship specified by a given key path. [`mutableOrderedSetValue(forKey:)`](/documentation/ObjectiveC/NSObject-swift.class/mutableOrderedSetValue(forKey:)) Returns a mutable ordered set that provides read-write access to the uniquing ordered to-many relationship specified by a given key. [`mutableOrderedSetValue(forKeyPath:)`](/documentation/ObjectiveC/NSObject-swift.class/mutableOrderedSetValue(forKeyPath:)) Returns a mutable ordered set that provides read-write access to the uniquing ordered to-many relationship specified by a given key path. ### Setting Values [`setValue(_:forKeyPath:)`](/documentation/ObjectiveC/NSObject-swift.class/setValue(_:forKeyPath:)) Sets the value for the property identified by a given key path to a given value. [`setValuesForKeys(_:)`](/documentation/ObjectiveC/NSObject-swift.class/setValuesForKeys(_:)) Sets properties of the receiver with values from a given dictionary, using its keys to identify the properties. [`setNilValueForKey(_:)`](/documentation/ObjectiveC/NSObject-swift.class/setNilValueForKey(_:)) Invoked by [`setValue(_:forKey:)`](/documentation/ObjectiveC/NSObject-swift.class/setValue(_:forKey:)) when it’s given a `nil` value for a scalar value (such as an `int` or `float`). [`setValue(_:forKey:)`](/documentation/ObjectiveC/NSObject-swift.class/setValue(_:forKey:)) Sets the property of the receiver specified by a given key to a given value. [`setValue(_:forUndefinedKey:)`](/documentation/ObjectiveC/NSObject-swift.class/setValue(_:forUndefinedKey:)) Invoked by [`setValue(_:forKey:)`](/documentation/ObjectiveC/NSObject-swift.class/setValue(_:forKey:)) when it finds no property for a given key. ### Changing Default Behavior [`accessInstanceVariablesDirectly`](/documentation/ObjectiveC/NSObject-swift.class/accessInstanceVariablesDirectly) Returns a Boolean value that indicates whether the key-value coding methods should access the corresponding instance variable directly on finding no accessor method for a property. ### Validation [`validateValue(_:forKey:)`](/documentation/ObjectiveC/NSObject-swift.class/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. [`validateValue(_:forKeyPath:)`](/documentation/ObjectiveC/NSObject-swift.class/validateValue(_:forKeyPath:)) Indicates whether the value specified by a given pointer is not valid for a given key path relative to the receiver. ### Deprecated Methods [`useStoredAccessor()`](/documentation/ObjectiveC/NSObject-swift.class/useStoredAccessor()) Returns `true` if the stored value methods [`storedValue(forKey:)`](/documentation/ObjectiveC/NSObject-swift.class/storedValue(forKey:)) and [`takeStoredValue(_:forKey:)`](/documentation/ObjectiveC/NSObject-swift.class/takeStoredValue(_:forKey:)) should use private accessor methods in preference to public accessors. [`handleQuery(withUnboundKey:)`](/documentation/ObjectiveC/NSObject-swift.class/handleQuery(withUnboundKey:)) Invoked by [`value(forKey:)`](/documentation/ObjectiveC/NSObject-swift.class/value(forKey:)) when it finds no property corresponding to `key`. [`handleTakeValue(_:forUnboundKey:)`](/documentation/ObjectiveC/NSObject-swift.class/handleTakeValue(_:forUnboundKey:)) Invoked by [`takeValue(_:forKey:)`](/documentation/ObjectiveC/NSObject-swift.class/takeValue(_:forKey:)) when it finds no property binding for `key`. [`storedValue(forKey:)`](/documentation/ObjectiveC/NSObject-swift.class/storedValue(forKey:)) Returns the property identified by a given key. [`takeStoredValue(_:forKey:)`](/documentation/ObjectiveC/NSObject-swift.class/takeStoredValue(_:forKey:)) Sets the value of the property identified by a given key. [`takeValues(from:)`](/documentation/ObjectiveC/NSObject-swift.class/takeValues(from:)) Sets properties of the receiver with values from a given dictionary, using its keys to identify the properties [`takeValue(_:forKeyPath:)`](/documentation/ObjectiveC/NSObject-swift.class/takeValue(_:forKeyPath:)) Sets the value for the property identified by `keyPath` to `value`. [`takeValue(_:forKey:)`](/documentation/ObjectiveC/NSObject-swift.class/takeValue(_:forKey:)) Sets the value for the property identified by `key` to `value`. [`unableToSetNil(forKey:)`](/documentation/ObjectiveC/NSObject-swift.class/unableToSetNil(forKey:)) Invoked if `key` is represented by a scalar attribute. [`values(forKeys:)`](/documentation/ObjectiveC/NSObject-swift.class/values(forKeys:)) Returns a dictionary containing as keys the property names in `keys`, with corresponding values being the corresponding property values. ### Constants [Key Value Coding Exception Names](/documentation/ObjectiveC/key-value-coding-exception-names) This constant defines the name of an exception raised when a key value coding operation fails. [NSUndefinedKeyException userInfo Keys](/documentation/ObjectiveC/nsundefinedkeyexception-userinfo-keys) These constants are keys into an `NSUndefinedKeyException` `userInfo` dictionary ## See Also [Key-Value Coding Programming Guide](https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/KeyValueCoding/index.html#//apple_ref/doc/uid/10000107i) --- 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)