Android Studio - view both Text and Design preview of layout

Open your [whatever].xml. At the bottom you'll see Design and Text. Select Text. If you still can't see the actual layout, only xml, then select "Preview" which is located at the right of the window, between Gradle and Maven Projects.

Click on preview while text is selected.

At first, select your desired .xml layout from the Project tab then use Code, Split and Design buttons to switch between the views. (Android Studio 3.6)

Code - Display only XML part

Split- Display XML and design both

Design- Only design part

It appears that in Android 3.6.1, the buttons to select Design, Split, or Code have been placed in the upper right of the XML layout screen.