Add texture into a button from URL - user-interface

Question

I'm trying to load an image as a texture, from a URL in a GUI function.
I did this UnityScript code, but it didn't work, giving this error:
OnGUI() can not be a coroutine.)
function Start () {
}
function Update () {
}
function OnGUI () {
var url = "http://images.wisegeek.com/duck.jpg";
var www : WWW = new WWW (url);
yield www;
if (GUI.Button(Rect(500,200,250,100),www.texture)){
Debug.Log("Image LOAD");
}
}

Answer 1

OnGUI() is called every frame to update the legacy Unity UI system. You should loading your texture once when the scene loads in Start(), or better yet somewhere before the scene that needs to use this texture. Typically if you have any dynamic resources to load you should do this at app startup, or in a loading scene between scenes.
Here's how to do it in Start() (I don't use Unityscript/js so my syntax might be wrong):
public bool isLoaded = false;
function Start() {
StartCoroutine(LoadResources());
}
function LoadResources() {
var url = "http://images.wisegeek.com/duck.jpg";
var www : WWW = new WWW (url);
yield www;
if (www.error == null) {
isLoaded = true;
}
}
function OnGUI() {
if (isLoaded) {
if (GUI.Button(Rect(500,200,250,100),www.texture)){
Debug.Log("Button pressed");
}
}
On another note: don't use the legacy Unity UI system. Use the new UnityEngine.UI instead (or a 3rd party UI system). The old system that utilizes OnGUI isn't really suitable for use in games. Plus the new system is easier to use and much more powerful.