Loading scene in Unity makes the references in that scene null - c#

I am making my first game in Unity and I'm trying to load the first level of it when the cutscene at the start ends. I don't know if it's possible to make the script do something after a video clip ends, so I wrote my code like this:
using UnityEngine;
using System.Collections;
using UnityEngine.SceneManagement;
public class CutsceneEnd : MonoBehaviour
{
// Start is called before the first frame update
void Start()
{
StartCoroutine("wait");
}
IEnumerator wait()
{
yield return new WaitForSeconds(36);
SceneManager.LoadScene(SceneManager.GetActiveScene().buildIndex + 1);
}
}
But the problem is not with my method of waiting for the end of the video, it's with the scene it loads. I can't move my character because all the references in the scripts are null. I have no idea what I did wrong.

Unity references should be stored in the scene file. Are you using any source control like git? If someone else did not push the changes to the .unityscene file or the .meta files for the associated scripts/prefabs, it might break the references.

I think we need some more information here.
If you referring to references (public variables) to Assets/GameObjects in the loaded scene, then you may have simply never placed the references in the first place. Unity's public variables should be saved within the Scene file and should always load with the Scene.
Double check to see if the references are actually null. Are you using an animation when you load into the Scene? This can keep you from being able to manual move anything. For example, if you animate the character when loading the scene, it could get stuck in the animation clip and you won't be able to move it.
Lastly, if you are referring to references created within the code to other scripts, objects, or variables, then these may break between scenes if you don't utilize 'DontDestroyOnLoad'.
Just spit-balling here, I need more information to correctly find the solution.

Related

Use script for GameObject creation / changes outside of runtime

I have a prefab, which is used multiple times in my game (it will not be instatiated during runtime, I only use the prefab by dragging it into scene view to build my level).
Inside this prefab are many locations, where a specific text is written. This text is unique for every prefab.
So, it is like:
InstanceA
TextA (multiple times inside the instance)
InstanceB
TextB (multiple times inside the instance)
and so on ...
At the moment, I see two options to do it:
I change every text manually in every instance. This would work, but is a little annoying, also I can see me making mistakes (like a misspelling or forget to change one of the texts).
I solve it by a script and change the texts in the Awake or Start method. This would work, but it must be done every time, I start the game.
What I would hope for would be a solution like 2) but not every time (because nothing changes, it es every time the same) but only once - so it is generated by a script but after that, it will be always there. Even when I'm not in runtime and just work in the scene view.
Do you know any approach to get something done like this?
Thank you!
If you wish to run a piece of code outside the run-time, you can use one of the following two options.
OnValidate method
OnValidate is triggered when your MonoBehaviour script is loaded or an inspector value has changed.
using UnityEngine;
public class TestScript : MonoBehaviour
{
private void OnValidate()
{
Debug.Log("test");
}
}
ExecuteInEditMode attribute
Adding ExecuteInEditMode to a MonoBehaviour class will make it function both during and outside the runtime. If you do not wish the script to function during the runtime, feel free to also use Application.isPlaying.
using UnityEngine;
[ExecuteInEditMode]
public class TestScript : MonoBehaviour
{
private void Update()
{
if (!Application.isPlaying)
Debug.Log("test");
}
}

Destroying Instantiated Clone Components Breaks Original Game Object Components?

Maybe im missing something obvious but to keep it short. I have working code for a character. When you "dash" I want to leave behind an after-image type effect, by cloning the player, removing its unneeded components and then applying a shader. Issue is as soon as I instantiate the clone the original player stops functioning (cant move etc). It still has all its components and everything as normal, and the clone does get the correct components removed. But it still breaks. As soon as I remove that line, its back to normal. Any ideas?
This is the only relevant code in the script that instantiates the clone.
private void DodgeEffect()
{
GameObject _DodgeSFX = Instantiate(gameObject, transform.position, transform.rotation );
Destroy(_DodgeSFX.GetComponent<PlayerController>());
Destroy(_DodgeSFX.GetComponent<PlayerCombat>());
Destroy(_DodgeSFX.GetComponent<WarpController>());
Destroy(_DodgeSFX.GetComponent<Animator>());
}
its because you are making a copy of gameObject. while Instantiate() returns a GameObject, it also returns whatever you put into the first section of the method. instead, make a seperate gameObject than the player in the editor, and make _DodgeSFX public so you can put the copy into the slot. Then, just instantiate that seperate GameObject and you wont have to destroy the components through script(because you remove the components in the editor), saving time
Ok so from some testing I think its down to the Unity.InputSystem only allowing 1 instance of each Input to be enabled at once. When I instantiated a clone of the player, it still goes through the Enable/Awake functions before those components are destroyed, and since the Inputs on that clone were never disabled, that becomes the "main" one. If I set the main player's scripts with Inputs deactive and then active again, it all works as normal. Note that the script was still working on the main character just fine, it was only the inputs that was broken. Im still not sure why this is the case, if its a limitation of the input system, or intentional, cant seem to find documentation of this experience anywhere.

Unity: Camera.main is failing after I switch scenes

I am having a weird issue with some of my code, and I could really use some help.
I have a script attached to a gameobject that is unique to a particular scene, so anything within Start() will only run when that scene is loaded. In this script, I am accessing Camera.main, since I use settings attached to the camera gameobject (it may sound inefficient, but it is necessary for the style of game we are creating). Anyway, if I start from that scene directly in Unity, it works just fine, but if I start from my intro scene and then load into the aforementioned scene, I get this error:
MissingReferenceException: The object of type 'Camera' has been destroyed but you are still trying to access it.
Your script should either check if it is null or you should not destroy the object.
The weird thing is, I can Debug.Log(Camera.main) and it gives me the name of the camera. So Camera.main is not null, and it is not destroyed like it says in the error message. Here is my full script:
private void Start()
{
Debug.LogError(Camera.main);
gameManager = FindObjectOfType<GameManagerScript>();
if (Camera.main == null)
{
Debug.LogError("Camera.main is null");
}
else
{
gameManager.LoadMusic(Camera.main);
gameManager.LoadAmbient(Camera.main);
gameManager.FadeStereoPan(Camera.main.gameObject.GetComponent<SwipeActivator>().stereoPanInNode);
}
}
The three functions above are custom functions I wrote, but I don't know why they would be causing the issue, since they work if I start up the scene directly.
I wasn't having this issue for months, and then all of a sudden, I am getting this error, even though I didn't change any of the code. Any help would be greatly appreciated.
I believe your MainCamera is being destroyed between scenes. Set it up as "DontDestroyOnLoad()"
See this Unity question:
https://answers.unity.com/questions/430141/need-the-same-main-camera-for-multiple-scenes.html
Ah, I fixed it. I dove into my custom functions and found that I was accessing a camera variable that is set at the beginning of the game, and then on each camera transition, but it was failing since I was loading a scene and no transitions that scene had yet to be completed. I just had to reassign that variable in the script above so it was not pointing to the destroyed object in the previous scene. Thank you JiveTurkey for pointing me in the right direction!

How to fix unintended scene buildIndex of -1 in Unity

Essentially, after testing a few level prototypes, I've decided to stick with my current game idea so I started creating a GameManager to control the flow of levels, etc. I don't have any additional libraries or asset packages being used outside of the default, but for some reason the buildIndex of all of my scenes is -1, which I learned according to the API, means that they're supposed to be loaded through an AssetBundle. Now I can't load anything with SceneManager and I'm not sure how to move forward. I did temporarily have the 2d-extras-master folder in the project as I assumed I'd be using it, but removed it after realizing I wouldn't need it. Does anyone know how to reset the buildIndices of my scenes to the values in the Build Settings? Any/All help is greatly appreciated!
Edit: I should also mention, that the latest Scene I added (when I still had the 2d-extras-manager) still retained a normal buildIndex of 0
Edit #2: So I've found that I can access the buildIndices of the other scenes amongst themselves. It's only when I try to access the buildIndices from my MainMenu Scene that things don't work
Edit #3: I've found a fix, but it doesn't necessarily answer the question. I found that I can force the LoadScene function to work if I know what the buildIndex is, but if I search for it via a scene name, it would return -1.
ex.
// where 1 is the buildIndex of Scene "Main" in BuildSettings
// works
SceneManager.LoadScene(1);
// doesn't work
int index = SceneManager.GetSceneByName("Main").buildIndex; //returns -1
SceneManager.LoadScene(index);
// also doesn't work (Where current scene is buildIndex 0)
SceneManager.LoadScene(SceneManager.GetActiveScene().buildIndex + 1);
SceneManager.GetSceneByBuildIndex or SceneManager.GetSceneByName and functions alike work only on loaded scenes. If scene isn't loaded it will return -1. Reason is, you can load scenes additively, so it's possible to have even 5 loaded scenes.
It's true that the api is lacking in many ways.
In your case you are trying to use it right after SceneManager.LoadScene(1);, int index = SceneManager.GetSceneByName("Main").buildIndex; returns -1 most likely because scene will be loaded on the next frame "officially".
You could try to wait 1 frame in coroutine and then do that. But usually you will have scene index or scene name to load/save it and not care about logic after scene has been loaded. You can create a manager which will store all of the loaded scenes where you could look up their build indices if you need them to decide what scene to load next.
Alternatively you can use Addressables package which handles a lot, it's hard to get into but scene loading works way better there in my opinion.
In the build menu, accessed by clicking in File on Unity Editor you can organize your scenes and add them to the flow like in this image
I'm not sure of it, but I'm supose when you didn't assigned a Scene to the flow, it get sceneIndex = -1. So load a scene, go to BuildSettings, add it to the build flow, do the same to all of them. I think this way you can solve it.
You can use this method to get buildIndex.
https://docs.unity3d.com/ScriptReference/SceneManagement.SceneUtility.GetBuildIndexByScenePath.html
And after checking the validity of the buildIndex, if the buildIndexis not equal to -1, then the scene exists in the build settings.
public static bool SceneExists(string scenePath)
{
return SceneUtility.GetBuildIndexByScenePath(scenePath) != -1;
}

Unity game manager. Script works only one time

I'm making simple game manager. I have a script, which will be accessible from all scenes in the game. And I need to check values of its variables after loading new scene. But my code runs only once after starting the simulation while an object with this script exists in all scenes. What is wrong? Why doesn't it work after loading a new scene?
In every Unity project you must have A PRELOAD SCENE.
It is quite confusing that Unity does not have a preload scene "built-in".
They will add this concept in the future.
Fort now you have to click to add a preload scene yourself.
This is the SINGLE GREATEST MISUNDERSTANDING for new programmers trying Unity!
Fortunately, it is extremely easy to have a preload scene.
Step 1.
Make a scene named "preload". It must be scene 0 in Build Manager.
Step 2.
In the "preload" scene make an empty GameObject called, say, "__app".
Simply, put DontDestroyOnLoad on '__app'.
Note:
This is the only place in the whole project you use DontDestroyOnLoad.
It's that simple.
In the example: the developers have made a one-line DDOL script.
Put that script on the "__app" object.
You never have to think about DDOL again.
Step 3
Your app will have (many) "general behaviors". So, things like database connectivity, sound effects, scoring, and so on.
You must, and can only, put your general behaviors on "_app".
It's really that simple.
The general behaviors are then - of course - available everywhere in the project, at all times, and in all scenes.
How else could you do it?
In the image example above, notice "Iap" ("in-app purchase") and the others.
All of your "generally-needed behaviors" - sound effects, scoring, and so on - are right there on that object.
Important...
This means that - of course, naturally -
...your general behaviors will have ordinary Inspectors, just like everything else in Unity.
You can use all the usual features of Unity, which you use on every other game object. Inspector variables, drag to connect, settings, and so on.
(Indeed: say you've been hired to work on an existing project. The first thing you will do, is glance at the preload scene. You will see all the "general behaviors" in the preload scene - sound effects, scoring, AI, etc etc. You will instantly see all the settings for those things as Inspector variables ... speech volume, playstore ID, etc etc.)
Here's an example "Sound effects" general behavior:
Looks like there's also a "voice over" general behavior, and a "music" general behavior".
To repeat. Regarding your "general behaviors". (Sound effects, scoring, social, etc etc.) These CAN ONLY GO on a game object in the preload scene.
This is not optional: there's no alternative!
It's that easy.
Sometimes engineers coming from other environments get caught up on this, because it seems like "it can't be that easy".
To repeat, Unity just plain forgot to "build-in" a preload scene. So, you simply click to add your preload scene. Don't forget to add the DDOL.
So, during development:
Always start your game from Preload scene.
It's that simple.
Important: Your app will certainly have "early" scenes. Examples:
"splash screen"
"menu"
Note. Tou CAN NOT use splash or menu as the preload scene. You have to literally have a separate preload scene.
The preload scene will then load your splash or menu or other early scene.
The central issue: "finding" those from other scripts:
So you have a preload scene.
All of your "general behaviors" are simply on the preload scene.
You next have the problem of, quite simply, finding say "SoundEffects".
You have to be able to find them easily, from, any script, on any game object, in any of your scenes.
Fortunately it is dead easy, it is one line of code.
Sound sound = Object.FindObjectOfType<Sound>();
Game game = Object.FindObjectOfType<Game>();
Do that in Awake, for any script that needs it.
It's honestly that simple. That's all there is to it.
Sound sound = Object.FindObjectOfType<Sound>();
Tremendous confusion arises because of the 100s of absolutely wrong code examples seen online.
It really is that easy - honest!
It's bizarre that Unity forgot to add a built-in "preload scene" - somewhere to attach your systems like SoundEffects, GameManager, etc. It's just one of those weird thing about Unity. So, the first thing you do in any Unity project is just click once to make a preload scene.
That's it!
A Detail...
Note that, if you really want to type even less (!) lines of code, it's remarkably easy - you can just use a global for each of these things!
This is explained in detail here , many folks now use something like this, a Grid.cs script ...
using Assets.scripts.network;
using UnityEngine;
static class Grid
{
public static Comms comms;
public static State state;
public static Launch launch;
public static INetworkCommunicator iNetworkCommunicator;
public static Sfx sfx;
static Grid()
{
GameObject g = GameObject.Find("_app");
comms = g.GetComponent<Comms>();
state = g.GetComponent<State>();
launch = g.GetComponent<Launch>();
iNetworkCommunicator = g.GetComponent<INetworkCommunicator>();
sfx = g.GetComponent<Sfx>();
}
}
Then, anywhere in the project you can say
Grid.sfx.Explosions();
It's just that easy, that's the whole thing.
Don't forget that each of those "general systems" is on, and can only be on, the DDOL game object in the preload scene.
DylanB asks: "During development it's quite annoying that you have to click to the preload scene every time before you click "Play". Can this be automated?"
Sure, every team has a different way to do this. Here's a trivial example:
// this should run absolutely first; use script-execution-order to do so.
// (of course, normally never use the script-execution-order feature,
// this is an unusual case, just for development.)
...
public class DevPreload:MonoBehaviour
{
void Awake()
{
GameObject check = GameObject.Find("__app");
if (check==null)
{ UnityEngine.SceneManagement.SceneManager.LoadScene("_preload"); }
}
}
But don't forget: what else can you do? Games have to start from a preload scene. What else can you do, other than click to go to the preload scene, to start the game? One may as well ask "it's annoying launching Unity to run Unity - how to avoid launching Unity?!" Games simply, of course, absolutely have to start from a preload scene - how else could it be? So sure, you have to "click to the preload scene before you click Play" when working in Unity - how else could it be?
#Fattie: Thanks for elaborating all this, it's great! There is a point though that people are trying to get through to you, and I'll just give it a go as well:
We do not want every instantiation of everything in our mobile games to do a "FindObjectOfType" for each and every every "global class"!
Instead you can just have it use an Instantiation of a static / a Singleton right away, without looking for it!
And it's as simple as this:
Write this in what class you want to access from anywhere, where XXXXX is the name of the class, for example "Sound"
public static XXXXX Instance { get; private set; }
void Awake()
{
if (Instance == null) { Instance = this; } else { Debug.Log("Warning: multiple " + this + " in scene!"); }
}
Now instead of your example
Sound sound = Object.FindObjectOfType<Sound>();
Just simply use it, without looking, and no extra variables, simply like this, right off from anywhere:
Sound.Instance.someWickedFunction();
Alternately (technically identical), just use one global class, usually called Grid, to "hold" each of those. Howto. So,
Grid.sound.someWickedFunction();
Grid.networking.blah();
Grid.ai.blah();
Here is how you can start whatever scene you like and be sure to reintegrate your _preload scene every time you hit play button in unity editor. There is new attribute available since Unity 2017 RuntimeInitializeOnLoadMethod, more about it here.
Basically you have a simple plane c# class and a static method with RuntimeInitializeOnLoadMethod on it. Now every time you start the game, this method will load the preload scene for you.
using UnityEngine;
using UnityEngine.SceneManagement;
public class LoadingSceneIntegration {
#if UNITY_EDITOR
public static int otherScene = -2;
[RuntimeInitializeOnLoadMethod(RuntimeInitializeLoadType.BeforeSceneLoad)]
static void InitLoadingScene()
{
Debug.Log("InitLoadingScene()");
int sceneIndex = SceneManager.GetActiveScene().buildIndex;
if (sceneIndex == 0) return;
Debug.Log("Loading _preload scene");
otherScene = sceneIndex;
//make sure your _preload scene is the first in scene build list
SceneManager.LoadScene(0);
}
#endif
}
Then in your _preload scene you have another script who will load back desired scene (from where you have started):
...
#if UNITY_EDITOR
private void Awake()
{
if (LoadingSceneIntegration.otherScene > 0)
{
Debug.Log("Returning again to the scene: " + LoadingSceneIntegration.otherScene);
SceneManager.LoadScene(LoadingSceneIntegration.otherScene);
}
}
#endif
...
An alternate solution from May 2019 without _preload:
https://low-scope.com/unity-tips-1-dont-use-your-first-scene-for-global-script-initialization/
I've paraphrased from the above blog to a how-to for it below:
Loading a Static Resource Prefab for all Scenes
In Project > Assets create a folder called Resources.
Create a Main Prefab from an empty GameObject and place in the Resources folder.
Create a Main.cs C# script in your Assets > Scripts or wherever.
using UnityEngine;
public class Main : MonoBehaviour
{
// Runs before a scene gets loaded
[RuntimeInitializeOnLoadMethod(RuntimeInitializeLoadType.BeforeSceneLoad)]
public static void LoadMain()
{
GameObject main = GameObject.Instantiate(Resources.Load("Main")) as GameObject;
GameObject.DontDestroyOnLoad(main);
}
// You can choose to add any "Service" component to the Main prefab.
// Examples are: Input, Saving, Sound, Config, Asset Bundles, Advertisements
}
Add Main.cs to the Main Prefab in your Resources folder.
Note how it uses RuntimeInitializeOnLoadMethod along with Resources.Load("Main") and DontDestroyOnLoad.
Attach any other scripts that need to be global across scenes to this prefab.
Note that if you link to other scene game objects to those scripts you probably want to use something like this in the Start function for those scripts:
if(score == null)
score = FindObjectOfType<Score>();
if(playerDamage == null)
playerDamage = GameObject.Find("Player").GetComponent<HitDamage>();
Or better yet, use an Asset management system like Addressable Assets or the Asset Bundles.
actually as a programmer who comes to unity world I see none of these approaches
standard
the most simplest and standard way: create a prefab, according to unity docs:
Unity’s Prefab system allows you to create, configure, and store a GameObject complete with all its components, property values, and child GameObjects
as a reusable Asset. The Prefab Asset acts as a template from which you can create new Prefab instances in the Scene.
Details:
Create a prefab within your Resources folder:
if you don't know how to create a prefab study this unity document
if you don't have resources directory create a folder and name it exactly Resources because it is a unity Special folder name
create a script with contents like below:
using UnityEngine;
public class Globals : MonoBehaviour // change Globals (it should be the same name of your script)
{
// loads before any other scene:
[RuntimeInitializeOnLoadMethod(RuntimeInitializeLoadType.BeforeSceneLoad)]
public static void LoadMain()
{
Debug.Log("i am before everything else");
}
}
assign it to your prefab
and you can make it even better:
use prefab and namespaces together:
in your prefab script:
using UnityEngine;
namespace Globals {
public class UserSettings
{
static string language = "per";
public static string GetLanguage()
{
return language;
}
public static void SetLanguage (string inputLang)
{
language = inputLang;
}
}
}
in your other scripts:
using Globals;
public class ManageInGameScene : MonoBehaviour
{
void Start()
{
string language = UserSettings.GetLanguage();
}
void Update()
{
}
}

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