Why Does My Unity Game Manager Script Only Run Once, and How Can I Make It Persistent Across Scenes?

Unity Game Manager: Cross-scenario persistence issues and solutions

Question:

Game Manager scripts designed to be persistent across scenes will only be executed once on project initialization, even if present in all scenes.

Reason:

Every Unity project requires a "preload scene" as the central hub for persistent objects and systems. This scenario must be specified as scenario 0 in the build settings.

Solution:

1. Create a preloaded scene:

   • In the build settings, add a new scene called "preload" and designate it as scene 0.

2. Add preloaded game object:

   • In the preload scene, create an empty game object named "__app".

3. Apply DontDestroyOnLoad:

   • Add the "DontDestroyOnLoad" script (or component) to the "__app" game object. This script ensures that the object and its components remain persistent across scene switches.

4. Place common behavior in preload scene:

   • All shared game logic, such as database connections, sound effects, and scoring, should be placed on the "__app" game object in the preloaded scene.

Find components in other scenes:

To access these persistent components from other scenes, you can use the static method "Object.FindObjectOfType()". For example:

<code class="language-C#">SoundEffects sound = Object.FindObjectOfType<SoundEffects>();
GameState state = Object.FindObjectOfType<GameState>();</code>

Optional optimization:

To reduce code duplication, consider using the following global script:

<code class="language-C#">public static class App
{
    public static SoundEffects SoundEffects { get; private set; }
    public static GameState GameState { get; private set; }

    static App()
    {
        GameObject appObject = GameObject.Find("__app");
        SoundEffects = appObject.GetComponent<SoundEffects>();
        GameState = appObject.GetComponent<GameState>();
    }
}</code>

Using this script you can access these components using a simplified syntax:

<code class="language-C#">App.SoundEffects.PlayExplosion();
App.GameState.CurrentLevel = 5;</code>

Development convenience:

In order to improve development efficiency, you can consider adding a script to the "preload" scene. If the "__app" object does not exist, the "preload" scene will be automatically loaded during project initialization. This ensures that the game starts from the "preload" scene every time "Play" is clicked.

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