Is it possible to call a function on Unity Program Start?

Question

I was wondering if there was a way in Unity that when I start my program on a scene it fires a function first, I should add that I want this one function to work regardless of what scene I'm in. So a simple Start function wont cut it. Not sure if this is possible in Unity?

public void ProgramBegins()
{
    //FIRES FIRST ON ANY SCENE
    //DO STUFF
}

Answer 1

RuntimeInitializeOnLoadMethodAttribute can help you :)

using UnityEngine;

class MyClass
{
    [RuntimeInitializeOnLoadMethod(RuntimeInitializeLoadType.BeforeSceneLoad)]
    static void OnBeforeSceneLoadRuntimeMethod()
    {
        Debug.Log("Before scene loaded");
    }
}

Answer 2

I use a prefab _AppStartup which is just an empty game object having a script AppStartup. Drag this in every scene and configure AppStartup to be executed as first like @maZZZu has stated.

AppStartup performs the following jobs:

• Global initialisation tasks when the app is started
• Switch to boot scene if have start an arbitrary scene in editor mode

• Scene specific initialisation tasks

  public class AppStartup : MonoBehaviour 
  {
      const int bootSceneNo = 0;
  
      public static bool veryFirstCallInApp =  true;
  
      void Awake ()
      {
          if (veryFirstCallInApp) {
              ProgramBegins ();
              if (Application.loadedLevel != bootSceneNo) {
                  // not the right scene, load boot scene and CU later
                  Application.LoadLevel (bootSceneNo);
                  // return as this scene will be destroyed now
                  return;
              } else {
                  // boot scene stuff goes here
              }
          } else {
              // stuff that must not be done in very first initialisation but afterwards
          }
          InitialiseScene ();
          veryFirstCallInApp = false;
          DestroyObject (gameObject);
      }
  
      void ProgramBegins()
      {
          // code executed only once when the app is started
      }
  
      void InitialiseScene ()
      {
          // code to initialise scene
      }
  }
  

So all you have to do is drag this prefab in every scene manually and give it -100 or whatever in the script execution order. Especially when the project grows and relies on a predefined scene flow it will save you al lot time and hassle.