5.2 — The Door: Opening It with Events

Compare against your own file rather than copying it. What has to match is the shape of the interaction, not its text: a single-frame key check, a scene search whose result is allowed to be nothing, a distance measured against a serialized number, and one call to Interact(). This version folds both refusals into one && condition, where the walkthrough used two separate early returns — on every frame the two files do the same thing.

// ------------------------------------------------------------------
//  REFERENCE FILE — Assets/Scripts/PlayerController.cs
//  Written to be read, not pasted. Build it with the walkthrough
//  above, one step at a time, then open this and compare.
//  If it is sitting in your project unchanged, that is the thing
//  to go and do now — the walkthrough is still above you.
// ------------------------------------------------------------------
using UnityEngine;

// PlayerController.cs - the interaction half, complete. Everything you built
// from 1.4 to 2.2 (input, movement, animation, coins, health) stays exactly as
// you wrote it; the two members below are the whole of what is new.
public class PlayerController : MonoBehaviour
{
    [SerializeField] private float moveSpeed = 5f;          // your number from 2.2
    [SerializeField] private float interactRange = 1.5f;    // how close is "near enough"

    private Rigidbody2D body;

    void Start()
    {
        body = GetComponent<Rigidbody2D>();                 // looked up once, per 2.2
    }

    void Update()
    {
        // ... the input, movement and animation lines from 1.4, 1.6 and 2.2 ...

        if (Input.GetKeyDown(KeyCode.E))
        {
            TryInteract();
        }
    }

    // One search, one measurement, one call. The search is allowed to come back
    // empty, so the two refusals are folded into the same condition - which
    // leaves exactly one line in this file that can do anything at all.
    private void TryInteract()
    {
        Lever lever = Object.FindFirstObjectByType<Lever>();

        if (lever != null &&
            Vector3.Distance(transform.position, lever.transform.position) <= interactRange)
        {
            lever.Interact();
        }
    }
}

Compare against your own file rather than copying it. Three things carry the lesson, and all three have to match: the access level you changed on onLeverOn, the subscription in Start(), and the unsubscription in OnDestroy(). This version keeps the method in a UnityAction field and hands the same value to both calls, where the walkthrough passed the method group straight into each one — the walkthrough's form is correct and shorter, and this is the form you reach for once there are several methods to remove.

// ------------------------------------------------------------------
//  REFERENCE FILE — Assets/Scripts/DoorOpener.cs (plus one line of Lever.cs)
//  Written to be read, not pasted. Build it with the walkthrough
//  above, one step at a time, then open this and compare.
//  If it is sitting in your project unchanged, that is the thing
//  to go and do now — the walkthrough is still above you.
// ------------------------------------------------------------------
using UnityEngine;
using UnityEngine.Events;

// DoorOpener.cs - this script's whole job is to be listening when the lever is
// pulled. It never touches Lever.cs at runtime: the lever calls OpenDoor without
// knowing this file exists, and it would call anything else the same way.
public class DoorOpener : MonoBehaviour
{
    [SerializeField] private Lever lever;        // the lever this door listens to
    [SerializeField] private GameObject door;    // the thing that disappears

    // The same method, kept as a value. AddListener and RemoveListener have to
    // be handed the SAME delegate, and holding it in a field is what makes the
    // removal exact rather than hopeful - and it is the only way once there is
    // more than one method to take off.
    private UnityAction onLeverPulled;

    private void Start()
    {
        onLeverPulled = OpenDoor;
        lever.onLeverOn.AddListener(onLeverPulled);
    }

    private void OnDestroy()
    {
        // The pair to Start(). A listener that outlives its object is a call
        // into something that is no longer there.
        lever.onLeverOn.RemoveListener(onLeverPulled);
    }

    private void OpenDoor()
    {
        door.SetActive(false);
    }
}