How to use IPropertyCollector to set preview for renderers?

i am making a custom timeline clip that switch materials (sharedMaterials). Unfortunately, i can't make
GatherProperties() works with renderers. i can make IPropertyCollector works with transform position, but not materials. i have goolged it for quite a while but no useful feedback. Do anyone has any suggestion?

i have tried ...

Code (CSharp):

1. driver.AddFromComponent(renderer.gameObject,renderer);
2. driver.AddFromName(renderer,"m_Materials");
3. driver.AddFromName(renderer,"m_SharedMaterials");
4. driver.AddFromName(renderer,"m_materials");
5. driver.AddFromName(renderer,"m_sharedMaterials");

 

I guess you need to use ExposedReference