How to add Default UI Material

,

image

In Control_Image, Update() has gameObject.SetActive(actives)
When I set actives = false, img disappear, it’s ok.
But after this, I set actives = true, ima doesn’t disappear.

// paste code here

And I think because "Default UI Material" disappears too but It doesn’t disappear when actives = true.
How add it again?