change property after adding to the layer

[mojtaba tabatabaie]

hi , I have an object3d and I've added that object to a ViewportLayer with this
code:

var mylayer:ViewportLayer = viewport.getChildLayer(myobject) ;


and when I want to change the alpha property of my object I change the
alpha property of "mylayer" . and everything's fine but after meeting
some conditions I want to change the material of my object3d . after I
change the material of my object3d , the change of alpha property of
"mylayer" doesn't work anymore !
I'll be really really appreciated if you help me on this
thanks