How to control alpha use slider

[jeaky]

Hi, I want use slider to control the alpha value, but I don't know how to write the code, I have writed some code bellow but not have any change in the scene. Anyone help me plz ?

var slider : float = 1;
var v1 : GameObject;

function OnSliderChange () {

     v1.renderer.material.color.a = slider;

}

[jeaky]

any help?

[ArenMook]

Widgets don't have a renderer. Get the UIWidget component and modify its alpha property.