GUI button working with GUI Textfield

Hello again

Early this week I was asking this: http://answers.unity3d.com/questions/737859/choose-a-texture-in-game.html I have solve this and I have now a textfield but that is not working in game ( in the inspector he does it but not in game) I thing I must a button collaborate with the textfield but how?

I have A script with www inside it, The script can have a link. The link must have A picture in it. If the link is good. The picture will show on a block. But this can only via the inspector. I have add a textfield to the script but I cant change the picture via the textfield. I thing I must add a button to achieve this here is the script:

 var url : String = "Hello World";
 
 function Start () {
         var www : WWW = new WWW (url);
 
         yield www;
 
         render.material.mainTexture = www.texture;
 }
 
 function OnGUI () {
        url = GUI.TextField (Rect (10, 10, 200, 20), url, 500);
 }

I dont have more.

(sorry for the bad english)