Scene management

Adding new scenes

Scenes are the different levels or screens of your game
You can add new scenes to your game with File > New scene
Then save it to your Scenes folder with File > Save scene
You can open another scenes from the Project window
Note: If you open a previously-made Unity project the first time, Unity won’t open any scenes, you have to do them manually from the Project window!

Building a game with multiple scenes

When you have multiple scenes, you need to add them to your build settings so you’re including them in the game
- File > Build Settings > Scenes in Build
- Either drag-and-drop your scenes here or click Add Open Scenes
- The top-most scene will be the one that gets loaded when the game starts
See Building for more about Build settings.

Scene manager

Script Reference: SceneManager
Scene Manager, uh, manages scenes
To use it, you need to import SceneManagement:
```
using UnityEngine.SceneManagement;
```

Loading a scene

To move between scenes, use SceneManager.LoadScene

  SceneManager.LoadScene(sceneBuildIndex);
  SceneManager.LoadScene(sceneName);

This unloads your current scene and loads the one you specified
Loading the scene you are currently in resets the scene (but not static variables!)

To get information about your current scene, use SceneManager.GetActiveScene():

if (SceneManager.GetActiveScene().name == "GameOver")
{
    // do stuff
} 

Loading complex scenes

To load a scene without unloading your current scene, use LoadSceneMode.Additive
```
SceneManager.LoadScene("YourScene", LoadSceneMode.Additive);
```
- Useful for big open worlds and interconnected areas
- If you use it, you might need to unload previously loaded levels as well
- Script Reference: SceneManager.UnloadSceneAsync

Data persistence between scenes

Learn: Data persistence between scenes
By default, no values persist when moving from a scene to another
You can change this by calling DontDestroyOnLoad and giving the gameObject you want to persist as an argument
```
private void Awake()
{
    DontDestroyOnLoad(gameObject);
}
```
- Note: this only works for root GameObjects - not for children!

Creating a data manager

We can create a data manager for bookkeeping score etc.
- LevelManager, GameManager, UIManager, etc…

We create a static variable that refers to it (here named instance)

$\Rightarrow$ we can use it easily from anywhere

public class ScoreManager : MonoBehaviour
{
    public static ScoreManager instance;

    private void Awake()
    {
        instance = this;
        DontDestroyOnLoad(gameObject);
    }
}

ScoreManager.instance.AddScore(1);

Prevent other instances of data manager from appearing

To make sure you only have one ScoreManager at all times, add these lines to the top of your ScoreManager’s Awake method.
```
  if (instance != null)
  {
      Destroy(gameObject);
      return;
  }
```
This is commonly known in software development as the singleton pattern.

Closing the game

Call Application.Quit(); when you want to close the game
- (Don’t worry, this does not close the Unity editor)

Extra: Do stuff when scene is loaded

Script Reference: SceneManager.sceneLoaded

// called first
void OnEnable()
{
    Debug.Log("OnEnable called");
    SceneManager.sceneLoaded += OnSceneLoaded;
}

// called second
void OnSceneLoaded(Scene scene, LoadSceneMode mode)
{
    Debug.Log("OnSceneLoaded: " + scene.name);
    Debug.Log(mode);
}

Extra: Listing multiple scenes

Usable for a Level select screen, etc

Get a list of files in a given path:

string [] files = System.IO.Directory.GetFiles(path);
foreach (string file in files)
{
    //Do work on the files here
}

Then, choose ones that .EndsWith(".unity")
Hint: Application.datapath tells the root of Assets path

Extra: Resources

Script Reference: Resources
Script Reference: Resources.LoadAll
- Loads all assets in a folder or file at path in a Resources folder.

Unity Cookbook. Scene management