iOS Auto Layout UIView Drawing cycle

In one of the WWDC videos, Apple said that the layout is done from top down, ie from superview to subview (after constraints are calculated from bottom up). Display is also done from top down.

My questions are: 1. At what point in the viewcontroller is a view's frame (origin and size) determined? I tried to log the size of a view (defined using auto layout), but it was always 0 0 0 0, which is odd, because the view is already generated in the simulator;

For an autoresized view, when is view.frame available?

2. Same question, except this time it is UIImageView.frame. I tried to log to console, even though the size is fit into the constraints, the logged UIImageView frame is 0 0 width_of_original_image height_of_original_image. But for other views like labels, the frame is printed correctly on the console.

It seems like that there is a mysterious auto layout engine that performs transform, and nobody knows what is going on inside the engine, but to check what is thrown onto the simulator display to figure out how the view was rendered by this engine???