I created a new project in order to try and get the basic features working for window resizing and the slowly moved it towards the target peice of my project. Doing this I tracked the problem down to this:
In my theme hierarchy I had this property:
<item name="android:windowFullscreen">true</item>
which was burried at the level of Theme.Black.NoTitleBar.FullScreen – An ancestor of my custom theme.
The documentation suggests that this is a “Flag indicating whether this window should fill the entire screen”. That sounds like a good thing to have if you have an app which takes up the whole screen… Except it still takes up the whole screen without the flag.
In fact, once you’ve taken this out, there is absolutely no change in the app at all… apart from adjustResize now works perfectly.