As I understand it, layout_height="fill_parent" means that the view will fill its parent vertically (no leap in logic there). That is, its top edge will align with the parent's top edge and its bottom edge will align with the parent's bottom edge.
And, as I understand it, the two alignParentXxx parameters also mean the the view's top and bottom edges will be aligned with those of its parent.
So, what's the difference? And why use both height and align?