Animate shader value

With a solution give by @rickster in this post : SceneKit - Crossfade material property textures, I try to implement an animation on fadeFactor. I try many things but nothing works as expected.

Here is some of my code :

• For shader :

  "uniform float fadeFactor;"

• In swift :

  let anim = CABasicAnimation(keyPath: "fadeFactor")
  anim.fromValue = NSNumber(value: 0.0)
  anim.toValue = NSNumber(value: 1.0)
  anim.duration = duration
  anim.repeatCount = .infinity
  node.geometry?.firstMaterial?.addAnimation(anim, forKey: "fadeFactor")
  

When I execute my code, no animation on fadeFactor property. What I'm doing wrong ?
In CABasicAnimation, I try different values for keyPath : geometry.firstMaterial.diffuse.contents, fadeFactor, etc.
I can't find which value I must give for parameters 'keyPath' and 'forKey' !

When I change value for fadeFactor with setValue function, it's OK :

node.geometry?.firstMaterial?.setValue(NSNumber(value: 0.5), forKey: "fadeFactor")

If somenone have a solution or can give me an example, it will be great.

Thanks in advance.