# enter(_:) Attempts to transition the state machine from its current state to a state of the specified class. ``` func enter(_ stateClass: AnyClass) -> Bool ``` ## Parameters `stateClass` The class of state into which to attempt a transition. ## Return Value if the transition was successful; otherwise . ## Discussion You build a state machine by creating a unique [`GKState`](/documentation/GameplayKit/GKState) subclass for each distinct state possible for the machine. The [`isValidNextState(_:)`](/documentation/GameplayKit/GKState/isValidNextState(_:)) method of each state object determines which other states a state machine is allowed to transition into from that state. Calling this method first tests whether a transition from the current state to the specified state is valid; if not, this method returns . If a transition is allowed, the state machine sends the [`willExit(to:)`](/documentation/GameplayKit/GKState/willExit(to:)) message to its current state object. Then, the new state object replaces the value of the [`currentState`](/documentation/GameplayKit/GKStateMachine/currentState) property. Finally, the state machine sends the [`didEnter(from:)`](/documentation/GameplayKit/GKState/didEnter(from:)) message to the new current state object, and this method returns . A newly created state machine’s [`currentState`](/documentation/GameplayKit/GKStateMachine/currentState) property is `nil`—to choose and enter an initial state, use the [`enter(_:)`](/documentation/GameplayKit/GKStateMachine/enter(_:)) method. In this case, the [`enter(_:)`](/documentation/GameplayKit/GKStateMachine/enter(_:)) call always succeeds. --- 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)