Why is my constructor called 3 times?

[johan21]

Hi, this is a Javascript / Unityscipt question:

This is TestScript.js

static public var concount : int = 0;



class MyClass 

{

	private var temp : int;

		

	function MyClass (ID : int)

	{

		TestScript.concount++;		

		Debug.Log("Constructor called no times: " + TestScript.concount );

		temp = ID;			

	}

}

And this is ExternalScript.js

private var classinst : MyClass = new MyClass(9);

function Start () 
{
		
}

Both scripts are attached to a GameObject.

Q1. According to my console output and my counter, when I execute the program, the constructor is called twice. It is doing my head in why this should be the case. I would have thought a variable declaration/initialization should only be called once, and therefore a constructor only once?

Q2. As if that wasn’t confusing enough, as I stop the execution in Unity, the console log indicates the constructor is called a 3rd time. Why?

By changing the declaration of classinst to inside the MonoBehaviour Start() function, the constructor is only called once and both problems go away.

Q3. Out of interest, I would really like to know how to go about debugging a problem like this in MonoDevelop. I have managed to crash Unity 3 or 4 times whilst trying to step through code in MonoDevelop with this simple example, whilst attached to the Unity Editor process. Should I be using ScriptableObject for my classes? Will this make my life easier?

Cheers for help

[MADmarine]

Unless you have multiple instances of this class in your scene, I think this has something to do with the funny way that Unity handles things in editor mode, I guess your monobehaviour that creates your test class is suffering from this:

http://unity3d.com/support/documentation/ScriptReference/index.Writing_Scripts_in_Csharp.html

"Never initialize any values in the constructor. Instead use Awake or Start for this purpose. Unity automatically invokes the constructor even when in edit mode. This usually happens directly after compilation of a script, because the constructor needs to be invoked in order to retrieve default values of a script. Not only will the constructor be called at unforeseen times, it might also be called for prefabs or inactive game objects.

Using the constructor when the class inherits from MonoBehaviour, will make the constructor to be called at unwanted times and in many cases might cause Unity to crash. Only use constructors if you are inheriting from ScriptableObject."

[Eric5h5]

You should write the code like this:

private var classinst : MyClass;

function Start () 
{
	classinst = new MyClass(9);
}

–Eric