[Bug] Child state machine's first state OnEnter triggers unintentionally

[Nitero]

The OnEnter method of the first state in a child state machine is always triggered when the parent state machine is created. I've made a minimal test setup to reproduce this. The child state machine is never actually entered, since the condition is never true. However we still get the log "Enter" once at the start, and never the "Exit" log.

internal class StateTester : MonoBehaviour
{
	private StateMachine _stateMachine;

	private void Start()
	{
		_stateMachine = new StateMachine();
		_stateMachine.AddState(
			"Start",
			new State()
		);
		_stateMachine.SetStartState("Start");

		StateMachine childStateMachine = new();
		childStateMachine.AddState("Child Start", new TestGameState());
		childStateMachine.SetStartState("Child Start");
		childStateMachine.Init();
		
		_stateMachine.AddState(
			"Child",
			childStateMachine
		);
		_stateMachine.AddTransition(new Transition(
			"Start",
			"Child",
			x => false
		));
		
		_stateMachine.Init();
	}

	private void Update()
	{
		Debug.Log("Current: " + _stateMachine.ActiveState.name);//always logs the start state
		_stateMachine.OnLogic();
	}
}

internal class TestGameState : State
{
	public override void OnEnter()
	{
		Debug.Log("Enter");//should not happen, but does
	}

	public override void OnExit()
	{
		Debug.Log("Exit");//never happens
	}
}

[Mr-Labyrinth]

Your Implementation

Unnecessary premature initialization occurs.

StateMachine childStateMachine = new();
childStateMachine.AddState("Child Start", new TestGameState());
childStateMachine.SetStartState("Child Start");
childStateMachine.Init(); // Should NOT be called here

At this point, childStateMachine has not been added to its parent state machine _stateMachine, and its IsRootFsm evaluates to true.

You incorrectly call Init(). This causes childStateMachine to trigger an early Enter via the source code below:

[Source Code Line 410-445](https://link.wtturl.cn/?target=https%3A%2F%2Fgithub.com%2FInspiaaa%2FUnityHFSM%2Fblob%2Fmaster%2Fsrc%2FStateMachine%2FStateMachine.cs&scene=im&aid=497858&lang=zh)

public override void Init()
{
    if (!IsRootFsm) return; // This return is skipped for childStateMachine, proceeds to OnEnter();

    OnEnter();
}

/// <summary>
/// Initializes the state machine and must be called before <c>OnLogic</c> is called.
/// It sets the activeState to the selected startState.
/// </summary>
public override void OnEnter()
{
    if (!startState.hasState)
    {
        throw UnityHFSM.Exceptions.Common.MissingStartState(this, context: "Running OnEnter of the state machine.");
    }

    // Clear any previous pending transition from the last run.
    pendingTransition.Clear();

    ChangeState(startState.state); // childStateMachine enters its own start state prematurely.

    for (int i = 0, count = transitionsFromAny.Count; i < count; i++)
    {
        transitionsFromAny[i].OnEnter();
    }

    foreach (List<TransitionBase<TStateId>> transitions in triggerTransitionsFromAny.Values)
    {
        for (int i = 0, count = transitions.Count; i < count; i++)
        {
            transitions[i].OnEnter();
        }
    }
}

Correct Implementation

StateMachine childStateMachine = new();
childStateMachine.AddState("Child Start", new TestGameState());
childStateMachine.SetStartState("Child Start");
// Remove this line: childStateMachine.Init();

....

_stateMachine.AddState(
    "Child",
    childStateMachine
); // Attach to parent state machine
_stateMachine.AddTransition(new Transition(
    "Start",
    "Child",
    x => false
));

_stateMachine.Init(); // Initialization handled by the parent state machine

This approach avoids premature execution of OnEnter() and ChangeState().

Note: I am not proficient in English. This reply was translated by AI. Please reply if anything is unclear.

[Nitero]

Oh thanks, didn't realize it's not suppoed to be called on the child.
Maybe adding a full example in the README for creating a child state machine would help? Seems like the existing example is incomplete