ImageView - have height match width?

Question

I have an imageview. I want its width to be fill_parent. I want its height to be whatever the width ends up being. For example:

Answer 1

For people passing by now, in 2017, the new best way to achieve what you want is by using ConstraintLayout like this:

And don't forget to add constraints to all of the four directions as needed by your layout.

Build a Responsive UI with ConstraintLayout

Furthermore, by now, PercentRelativeLayout has been deprecated (see Android documentation).