# CustomAction A protocol that represents an action whose behavior is implemented outside of TabletopKit. A custom action that can be applied to a `TableState`. ``` protocol CustomAction ``` ## Topics ### Creating a custom action [`init?(from: some TabletopAction)`](/documentation/TabletopKit/CustomAction/init(from:)) Creates an instance of `CustomAction` initialized from the provided `TabletopAction`. If the provided action is not a custom action, this initializer returns `nil`. ### Applying the action [`func apply(table: inout TableState)`](/documentation/TabletopKit/CustomAction/apply(table:)) Implement this function to perform the changes to the table state that this action represents. It is important that the code performed in this function is only a function of the provided table state and the data of the action instance. ### Validating the action [`func validate(snapshot: TableSnapshot) -> Bool`](/documentation/TabletopKit/CustomAction/validate(snapshot:)) Implement this function to detect whether the action is valid and should be applied given the state of the table represented by `snapshot`. If not implemented, the action is always considered valid. It is important that the validation for a given action is only a function of the given snapshot and the data of the action instance. --- 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)