09 Persistent: Surviving Scene Loads

📍 Demo Info

• Scene Preview

  

• Scene Path

  Assets/TinyGiants/GameEventSystem/Demo/09_PersistentEvent/09_PersistentEvent_1.unity

  Goal

  To demonstrate Persistent Events. Normally, event listeners are cleared when a scene unloads. By checking the Persistent flag, you can make specific event bindings survive scene transitions, which is essential for global systems like Music, Inventory, or Achievements.

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📝 Description

The Scene Transition Problem In Unity, when you load a new scene, all objects (and their event listeners) from the previous scene are destroyed.

• Standard Event: Listeners are wiped. The connection is broken.
• Persistent Event: Listeners are stored in a global PersistentManager and remain active.

The Experiment We have two Turrets controlled by separate events:

1. Turret A (Red): Driven by a Persistent Event.
2. Turret B (Blue): Driven by a standard Non-Persistent Event.

We will fire them, reload the scene, and see who survives.

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🛠️ Scene Setup

The architecture here is slightly more advanced to support scene reloading.

1. Persistent Receiver: A Singleton object marked DontDestroyOnLoad. It holds the logic for both turrets.
2. Scene Setup Script: Since the Receiver survives but the Turrets are destroyed/recreated, this script re-injects the new Turret references into the Receiver every time the scene loads.
3. UI Controls:
   • Fire A / Fire B: Triggers the respective events.
   • Load Scene 2: Reloads the current scene (simulating a level change) to test persistence.

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🎮 How to Test

1. Enter Play Mode.
2. Phase 1: Initial Test
   • Click "Fire A". Turret A fires. (Success)
   • Click "Fire B". Turret B fires. (Success)
3. Phase 2: The Purge
   • Click "Load Scene 2".
   • Effect: The scene reloads. The old Turrets are destroyed. New Turrets are spawned. The GameEventManager cleans up all standard listeners.
4. Phase 3: Survival Test
   • Click "Fire A".
   • Result: Turret A fires! The link survived. ✅
   • Click "Fire B".
   • Result: Silence. Turret B does nothing. The link is dead. ❌

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🔑 Key Configuration

1. Event Definition (Editor)

We use two identical Void events.

2. Persistence Toggle (Behavior)

This is the only configuration difference.

OnTurretA (Persistent):

• Open Behavior Window.
• Check [x] Persistent Event at the bottom.
• This tells the manager: "Never unsubscribe these listeners automatically."

OnTurretB (Standard):

• Uncheck [ ] Persistent Event.
• This tells the manager: "Clean me up when the scene unloads."

3. Raiser Assignment (Inspector)

The Raiser references both events.

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💻 Code Walkthrough

1. The Global Receiver (PersistentEventReceiver.cs)

This script is a Singleton that survives scene loads.

public class PersistentEventReceiver : MonoBehaviour
{
    // Singleton Pattern to survive scene loads
    public static PersistentEventReceiver Instance;

    private void Awake()
    {
        if (Instance == null)
        {
            Instance = this;
            DontDestroyOnLoad(gameObject); // <--- Key to persistence
        }
        else Destroy(gameObject);
    }

    // Bound to 'OnTurretA' (Persistent)
    // This method will still be called after scene load.
    public void OnFireCommandA()
    {
        _isFiringA = true; // Starts the coroutine
    }

    // Bound to 'OnTurretB' (Standard)
    // This binding is LOST after scene load because the event wasn't marked Persistent.
    public void OnFireCommandB()
    {
        _isFiringB = true;
    }
}