In Split-Screen, Your Orientation Flips

Many of you have no doubt discovered this already, but for those who
have not: whether you get portrait or landscape resources is dependent
upon the aspect ratio of the window, not the device, on
Android 7.0. So, if the
device is in portrait, and your activity is being shown in normal mode,
you will have portrait resources. But, if the user then moves the device
into split-screen mode, putting your activity into one pane, you will
undergo a configuration change, and now use landscape resources, even
though the device itself did not rotate. The same holds true for
the inverse case (device in landscape, with entry into split-screen
switching your activity from landscape to portrait resources).

This is not terribly shocking, though it was not something that I had
considered when Android 7.0���s multi-window was announced. I only infrequently
use -land resources (and never -port), preferring instead to
tie orientation and screen size together (e.g., -w640dp). So, I was
focusing on the smaller window size, not so much its orientation.

However, this is another example of where we need to take care to ensure
that the switch from normal to split-screen mode (or back again) is
a smooth one. Having a radically different UI in one orientation versus
the other means that the user will see a radically different UI when
she switches between normal and split-screen mode, which may not be a good
idea. Worse, if and when the mythical freeform multi-window mode becomes
available, the user may see a radical UI change just by a small window
resize operation, one that happens to move the window between
portrait and landscape aspect ratios.