I watched Apple a design session from Apple WWDC 2018 called Designing Fluid Interfaces last week. It was a great talk that walks us through what fluidity means, why it matters, and how Apple goes about it in practice. I admire Apple’s thoughts behind design at such a granular level, and I am a big advocate of the concept of fluid interfaces. However, I found something not quite fluid.
One day I was in Google maps and listening to music on iPhone X. I switched to the music app by swiping right along the bottom edge of the screen. I paused a song, then I tried to switch back to Google maps by swiping left. But I couldn’t.
Do you see what goes wrong here? Before getting to the problem, let’s take a closer look at how multitasking works in iOS.
How multitasking works on iPhone X
Before diving into why, it is necessary to call out that there are two ways to switch apps on iPhone X:
- Swipe up from the bottom of the screen and pause.
- If you’re in an app, swipe right or left along the bottom edge of the screen. (I’m surprised that some of my friends don’t know about this feature after using iPhone X for half of a year)
For the first method, consider the system is mapped out in a three-dimensional space.
- Apps are stacked up like a deck of cards.
- Swipe left and right to traverse apps in the z-axis.
- Tapping an app will bring the app to the front.
However, when using the second method, users may have a completely different mental modal because of the interaction. Being able to swipe left and right to switch apps tends to give us an impression that apps are spread out at the same level across the x-axis, but in fact, they are not.
Moreover, the switching animation also implies that apps are sitting side by side.
How multitasking works on other iPhones
On iPhones equipped with 3D Touch, actually there are also two ways to switch apps.
- Double-click the Home button.
- Force touch the left edge of the screen and swipe right.
Similarly, the second method is also a shortcut to switch apps. However, unlike iPhone X, you can only switch between two recently used apps. It conforms to the way the iOS spatial interface works.
The spatial inconsistency leads up to confusions, and it explains why in the example I mentioned above, I subconsciously swiped, the opposite direction, left to go back to Google maps.