Game states & passing data between scenes

Question

I'm not entirely sure if I'm doing this right, but I always considered the scene system in Unity as some sort of state management (rather than e.g. a level system) which allows to group the contents (entities, components) into the usual main states of the game (menu, ingame), which can then be invoked or replaced together.

Now I have a very specific concern and I have no clue how to deal with that in Unity, mostly because of it's abstractions from code and other restrictions:

My game features a procedurally generate terrain where as I'd like to tweak the generator before actually launching it. The tweaking is done in some sort of 'pre-game' state (as part of the main menu) where the values are stored in e.g. TerrainData model class. Usually in other engines, I'd to it like this:

1. Providing an UI within the menu state to tweak the parameters of the game
2. Storing the parameters in a view model (and data model)
3. Instantiate the ingame state (which requires said data model in the .ctor
4. Pass the data model to a generator and start the generation

Now, here are the main problems:

• Most types in unity (scenes, monobehaviors) do not allow constructors because they use it for themselves
• It doesn't seem possible to instantiate scenes manually (there's only e.g. Application.LoadLevel("") which only takes the name of the scene, not a instance reference etc.
• it doesn't seem possible to pass data between scenes, without reverting to awkward workarounds such as singletons, playerprefs, DontDestroy etc. which are all not really suitable for this case.

So, how can I properly solve this? Is there a better way to manage states rather than scenes? Prefabs maybe?

Backlink to UntityAnswers question: http://answers.unity3d.com/questions/1149480/game-state-management-and-passing-data-between-sce.html

Answer 1

Singletons, PlayerPrefs and the DontDestroyOnLoad flag are already three ways to pass data between scenes. There is also a fourth one: static variables which do not use the Singleton pattern but are only available to the local class.

There is also SceneManager.LoadScene ("play_scene", LoadSceneMode.Additive); which loads a new scene without destroying anything in your current scene. That means you can use this method from your UI to load the play-scene without destroying your UI and the data model it operates on and then initialize the scene from the UI. Caveat: You can't use the Unity editor to assign objects from the Game-Scene to inspector properties of objects in the UI-Scene, so you will have to extract them from the scene graph with GameObject.Find and GetComponentInChildren. After setting up the play-scene, you can remove everything which belongs to the generator-scene with SceneManager.UnloadScene("generator_scene");.

Another option would be to implement your generator tweaking GUI in the actual game scene. Put your whole game scene in one parent-object and set it to deactivated when the scene loads. Then put the whole generator-UI into a different object and activate it. Put any shared stuff (like the model you operate on) in a third one.

When the user made their input and clicks "OK", deactivate the generator UI game-object and activate the actual game game-object.