Swift State machine

SwiftStateMachine.swift

//: # State machine: handling three state and transition

import GameplayKit

class RetrievingDataState: GKState {
    
    override func isValidNextState(stateClass: AnyClass) -> Bool {
        print("\n---> \(stateClass) class")
        return (stateClass == DataAvailableState.self) || (stateClass ==  DataNotAvailableState.self)
    }
    
    override func didEnterWithPreviousState(previousState: GKState?) {
        // Perform here the actions that you want to do with your UI when it enters this state like for example, showing and starting an activity indicator
        print("searching data start")
    }
    
    override func willExitWithNextState(nextState: GKState) {
        // Perform here the actions that you want to do with your UI when it exits this state like for example, stopping the activity indicator.
        print("End of search")
    }
    
}

class DataAvailableState: GKState {
    
    // Can't translate from DataNotAvailableState
    override func isValidNextState(stateClass: AnyClass) -> Bool {
        print("\n---> \(stateClass) class")
        return stateClass == RetrievingDataState.self
    }
    
    override func didEnterWithPreviousState(previousState: GKState?) {
        // Perform here the actions that you want to do with your UI when it enters this state.
        print("data available: show it")
    }
    
    override func willExitWithNextState(nextState: GKState) {
        // Perform here the actions that you want to do with your UI when it exits this state.
        print("data available end")
    }
}

class DataNotAvailableState: GKState {

    override func isValidNextState(stateClass: AnyClass) -> Bool {
        print("\n---> \(stateClass) class")
        return stateClass == RetrievingDataState.self
    }
    
    override func didEnterWithPreviousState(previousState: GKState?) {
        // Perform here the actions that you want to do with your UI when it enters this state.
        print("data not available state started: show not found message")
    }
    
    override func willExitWithNextState(nextState: GKState) {
        // Perform here the actions that you want to do with your UI when it exits this state.
        print("data not available state end")
    }
}

// create states
let retrievingDataState = RetrievingDataState()
let dataAvailableState = DataAvailableState()
let dataNotAvailableState = DataNotAvailableState()

// state machine
let stateMachine = GKStateMachine(states: [retrievingDataState, dataAvailableState, dataNotAvailableState])

stateMachine.enterState(RetrievingDataState)
stateMachine.enterState(DataAvailableState)
// valid state transition
stateMachine.enterState(RetrievingDataState)
stateMachine.enterState(DataNotAvailableState)

Output:

searching data start

---> DataAvailableState class
End of search
data available: show it

---> RetrievingDataState class
data available end
searching data start

---> DataNotAvailableState class
End of search
data not available state started: show not found message