Header, Input, and Choice

I am very new to iOS programming and I am trying to get started on making an App for scientific calculations but cant seem to find how to do a simple pull-down menu that will allow a user to assign a unit of measurement to a value they just input.

I will have many inputs, typically four per row. Each input will have a title/header text then below the title/header there will be an input block and, the part I am having the most problem with, a pull-down menu that will allow a user to select a unit of measurement, as an example, inches or millimeters. When the selection is choosen I would like the menu to shrink and display the selected value. Wondering if someone can lead to an example?

I would like the selected unit of measurement to look like the header text meaning no frame or any indication that the item is a pulldown menu because sometimes some units will not have a unit of measurement because they could be a percentage where I would have the percent symbol below the input. The idea is to have a very uniform display of headers, input blocks, and units.

I have done this entire app on an android and trying to make the same thing for iOS and find it hard to get started. ANy guidance is greatly appreciated.