# HMCharacteristicWriteAction An action in an action set that writes a value to a characteristic. ``` class HMCharacteristicWriteAction where TargetValueType : NSCopying ``` ## Overview Action sets are instances of [`HMActionSet`](/documentation/HomeKit/HMActionSet). ## Topics ### New Methods [`- initWithCharacteristic:targetValue:`](/documentation/HomeKit/HMCharacteristicWriteAction/init(characteristic:targetValue:)) Initialize a characteristic write action with a specified characteristic and target value. [`characteristic`](/documentation/HomeKit/HMCharacteristicWriteAction/characteristic) The characteristic whose value is to be written by the action. [`targetValue`](/documentation/HomeKit/HMCharacteristicWriteAction/targetValue) The value that will be written to the characteristic when the action is executed. [`- updateTargetValue:completionHandler:`](/documentation/HomeKit/HMCharacteristicWriteAction/updateTargetValue(_:completionHandler:)) Updates the target value. ## Relationships ### Conforms To [`CustomDebugStringConvertible`](/documentation/Swift/CustomDebugStringConvertible) [`Hashable`](/documentation/Swift/Hashable) [`CVarArg`](/documentation/Swift/CVarArg) [`SendableMetatype`](/documentation/Swift/SendableMetatype) [`CustomStringConvertible`](/documentation/Swift/CustomStringConvertible) [`Sendable`](/documentation/Swift/Sendable) [`NSObjectProtocol`](/documentation/ObjectiveC/NSObjectProtocol) [`Equatable`](/documentation/Swift/Equatable) ### Inherits From [`HMAction`](/documentation/HomeKit/HMAction) --- 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)