1

Here is the example of "GetComponentsInChildren" from the Unity Script Reference:

var hingeJoints : HingeJoint[];
hingeJoints = gameObject.GetComponentsInChildren(HingeJoint);
for (var joint : HingeJoint in hingeJoints) {
joint.useSpring = false;
}

Here is what I have in my script:

private var colliders : MeshCollider[];
function Awake ()
{   
    colliders = gameObject.GetComponentsInChildren(MeshCollider);
}

And I am getting an Invalid Cast error for that. (I have also tried making it more generically just "Collider" as opposed to "MeshCollider", but still the same error.)

What gives?

EDIT: Ok, here's my JS workaround that I came up with before I saw Jessy's edit/addition below... (are we doing essentially the same thing?)

private var colliders : MeshCollider[];
private var tempCol : Array;

function Awake ()
{
    tempCol = new Array();  
    for (var col : MeshCollider in gameObject.GetComponentsInChildren(MeshCollider))
        tempCol.Push(col);
    colliders = tempCol.ToBuiltin(MeshCollider);
}

Also, I figure doing it this way is OK performance-wise for me, since I do it once in the Awake() function, but I don't think it would be good to do it in an Update()...

2

http://answers.unity3d.com/questions/39864/invalidcastexception-in-a-code-from-script-reference

It's a good question, but was already asked, so I voted to close this; I believe the answers ought to be collected in one place.

As for your edit, that works, but I consider the Array class obsolete, now that UnityScript supports generics. Also, your script requires the use of dynamic typing. It doesn't matter, because it's a small bit of code running once, but you should at least know how to do better. (Using #pragma strict at the top of your scripts will help you write efficient code.) A couple more general tip: there's no point in using gameObject because GetComponentsInChildren is also a method of Component. And there's no reason to define a temporary variable outside of a function, if its scope is only within the function.

So, your code, with a List instead of a Unity Array:

private var colliders : MeshCollider[];

function Awake () {
    var colliderList = new List.<MeshCollider>();  
    for (var component in GetComponentsInChildren(MeshCollider)) 
        colliderList.Add(component as MeshCollider);
    colliders = colliderList.ToArray();
}

But this kind of thing is why Array.ConvertAll exists. I don't know if it's faster or slower, but I like the look of it better:

colliders = System.Array.ConvertAll(
    GetComponentsInChildren(MeshCollider),
    function (component) component as MeshCollider
);

Here are pages that might be helpful to you, if you don't know what that code means yet: http://unity3d.com/support/documentation/Manual/MonoUpgradeDetails.html

Array.ConvertAll

The syntax for lambda expressions is different in C#, but this example is less verbose than the MSDN's.

Finally, if you want optimum performance, you probably should just not bother with a List or ConvertAll, and implement the conversion yourself:

var colliderComponents = GetComponentsInChildren(MeshCollider);
colliders = new MeshCollider[colliderComponents.Length];  
for (var i = 0; i < colliders.Length; ++i) 
    colliders _= colliderComponents *as MeshCollider;*_
_*```*_
_*<p>I don't think that looks any better or worse than the List method.</p>*_
_*<p>But the best thing to do, would be to report the useless error that stops this ideal code from compiling:</p>*_
_*```*_
_*colliders = GetComponentsInChildren.<MeshCollider>();*_
_*```*_
_*<p>And man, I've written so much here, now, that this question probably shouldn't be closed anymore.  :-P</p>*_