Does Unity have a constructor when loading a scene? - unity3d

Question

I would like to populate the UI when I load a scene, with the correct data, instead of placeholders.
When I call "LoadSceneAsync", what would be the first object that is called, so I can fill the UI label with the correct data? I know that there is a scene GameObject, but I am not sure if that would fit my needs.
I am looking for some sort of constructor, called when a new scene object is loaded; to plug in my setup function.

Answer 1

You say
Indeed I did use "onlevelwasloaded" but the UI element may not be there, ready to go, when I invoke it, which lead to errors
That would be an incredibly sever bug in Unity! :)
Could it be that you are mixing-up Awake and Start somewhere?
One way to think of it is once you call Start, you know all the Awake have already run.
When I call "LoadSceneAsync", what would be the first object that is called, so I can fill the UI label with the correct data
You are still within the same frame.
Once you see LoadSceneAsync you can be absolutely assured everything is Awake 'd.
Or indeed once you use Start you can be absolutely assured everything is Awake 'd.
1) could it be that in some of your UI elements (or whatever) you are doing something in Start which you should do in Awake?
2) if (for some reason) you want to "wait until the next frame", perhaps just during development - then do that, wait a frame. You'll see a flicker, but if that's what you want to do (for some reason) do that.
3) note that if you mean you want to go to the net to get something, well of course you have to wait frames (use Update/coroutine) until the information comes back from the net, obviously. (How else could it be?)
Note that in practice, one should be using UnityEngine.Events.UnityEvent everywhere.

Answer 2

Maybe this is what you are looking for http://docs.unity3d.com/ScriptReference/MonoBehaviour.OnLevelWasLoaded.html

Answer 3

Relying on Unity internal functioning is not always the way to go. Particularly when dealing with RESTApi (which is somehow what you are dealing with here).
You cannot assume one object will be ready before another except if you control it.
Add a Controller script that uses Awake. In the Awake, call all the methods you are needing and use some callback to generate secondary code when primary is ready.
public class MyController: MonoBehaviour{
private ServerRequestController serverCtrl = null;
private UIController uiCtrl = null;
private void Awake(){
serverCtrl = this.gameObject.AddComponent<ServerRequestController>();
uiCtrl =this.gameObject.AddComponent<UIController>();
serverCtrl.GetData(uiCtrl.SetUI);
}
}
public class UIController:MonoBehaviour{
public void SetUI(Data data)
{
SetTopImage(data.topImage);
SetBottomImage(data.bottomImage);
// And so on
}
}
public class ServerRequestController:MonoBehaviour{
public void GetData(Action onCompletion){
// This may be a coroutine if you fetch from server
Data data = GetDataFromSomewhere();
// At this point, your data is ready
onCompletion(data);
}
}
Thanks to this, you are now able to know exactly when a piece of code is ready.