Even though I don't really understand the need for foldable devices, it hasn't stopped phone companies from pushing the boundaries when it comes to the definition of a 'display surface' and what it can do.

Previous questions on design strategies haven't really yielded much response on UXSE, because most of our attention is still focused on how to cope with the divergence in display resolution and aspect ratios, let alone having to deal with multiple screens.

However, given the consensus that we are almost designing in an age where 'mobile-first' and 'content-is-the-king' dominate most discussions, I think the case for considering what the uncharted waters of foldable devices and its impact on interface design is interesting to consider.

My hypothesis is that they will be treated like multi-screen devices in terms of the user workflow and interactions, but I am wondering if there is any research or use cases to support this (since I haven't dabbled in this area yet).


Put plainly: I dissent.

I think the main fault in your logic is this: The entire purpose of a folding display is to eliminate your need to treat it like two separate displays. It's literally one display, which simply folds. Unfolded, it takes on the form factor of a regular phone or of a tablet. These are familiar ecosystems.

Yes, there are other "foldable" form factors out there. These are ones that are truly multi-display. Devices like the Galaxy fold, an open book form factor, with one smaller screen in the front and one large one inside. However, this is still just a tablet with a phone display on the outside. Again, beside from how an app may "travel" from one screen to another, there's nothing new.

Things get interesting when you start looking at devices like the Microsoft Surface Duo, and the Huawei Mate X. The Surface Duo not only has a secondary display, but it also comes with a keyboard that folds over it, putting one display in a "keyboard mode". The OS is very dynamic, but for the apps, what's really changed? They still never climb outside of one screen.

The problem is this: developing an app that supports multiple screens is silly, and device manufactures know this, because they don't only manufacture multi-screen devices. For devices like the Nintendo DS, that was the only device developers needed to develop for. For Android or iOS developers, what incentive do developers have to spend a significant chunk of time supporting an optional feature that very few of their users can even enjoy?

So, for now, multi-display devices are simply "open an app in each screen" while the OS juggles all the nuanced complexities. There would have to be a massive shift in the mobile market for this to change. Most, if not all, mobile devices would need to become multi-display. And that just seems wildly improbable.

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    It is great to see ideas being challenged, and I for one hadn't really considered it from this particular perspective so I think this response takes the bounty! – Michael Lai Mar 11 '20 at 2:05

Multi-screen mode is a plausible default mode given the history and wide install base of existing foldable devices, namely the Nintendo DS.

The DS and variations like the 3DS, 2DS, XL, Lite, etc. have been around for more than 15 years at the time of this writing, with hundreds of millions of users. So it sets a fairly good precedent of multi-screen mode being the primary way to use such a device. (There were a few exceptions that were generally non-interactive, such as cutscenes.)

This mode was largely a by-product of the hardware design itself. Users had to use direct input (touch) on one and indirect input (buttons) for the other. The screens were also separated by a bezel and were even different sizes and/or resolutions in later models.

The wide install base suggests that many future users of foldable phones, tablets, or other devices will be familiar with a multi-screen mode of operation, where each screen contains separate (but often connected) content and can be interacted with independently.

Reference: Wikipedia - Best selling game consoles

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    The multi-screen DS devices are great examples! That said, the difference in implementation would need to be considered. DS devices are only half touchscreen, with buttons to assist in interaction. The foldable phones are (most likely) both touchscreens. This implementation difference will likely lead to software differences. Also, due to the screen differences, some games defined explicit roles for each screen: view the character and world on the top screen, see a map or abstract interaction on the bottom screen. It's possible productivity apps could do the same. – Benjamin S Mar 9 '20 at 13:28

I'd say your hypothesis will mostly play out, because it is the easiest approach requiring the least (or no) change to most apps. Hybrid and web apps will be the least capable of dealing with new foldable features, so they certainly won't be pushing the envelope. Also it is cheaper (factoring in warranty) an easier to make a device that folds and has multiple screen than it is to use a folding display or multiple folding displays.

A very Android-oriented rant:

Android's APIs provide a few features related to foldables and/or multi-screens, and the documentation gives the impression that one can make use of these for both "form factors".

Launch adjacent allows an app to open another Activity (as a separate Task) "adjacent" to the current one, i.e. resulting in two windows side-by-side. That is a similar concept to launching in a separate screen. Note there is also a means to explicitly open an Activity in another screen. Android 10 introduces new folding display targeted APIs including a means to specify the default size, minimum and maximum sizes, and position (using Gravity) of Activities within a screen.

I've also seen the use of RemoteViews for the other screen on a foldable device (i.e. when device folded closed), which is treating the other screen like a Home Screen Launcher. That means many constraints but much better longevity (less power consumption), so it makes sense for displaying glance-able status updates in lieu of the big screen being unfolded.

Where they won't behave so much like multi-screen devices is when manufacturers allow Activity resizing, then apps will just stretch unless they make better use of the newfound screen real estate. That will see mobile devices behaving a bit more like a desktop computer.

There will be more room for innovations in software UI and UX, such as having UI and even interactions span across multiple windows (a swipe could carry across from one Activity to another while they are side-by-side on the same touch surface). Whether any of these will actually serve a purpose that returns well on the investment to develop is yet to be seen. I imagine foldables won't be very popular and critical mass won't be achieved (such as we've seen with Google Glass, Google Wear, Google Home, a lot of Google products actually), so where they could make most use is in organisations that buy a lot for their staff and develop internal tools that leverage foldable form factors to achieve greater productivity.


The topic seems to be about the future of devices:

In real examples it can be seen empirically that computers with a touch panel, becomes smart: enter image description here

I think a lot depends on the type of work/task the user is accomplishing.

I can't imagine programming on a tablet or phone - many screens are needed for complex projects.In this case - a simple interaction enter image description here allows you to change screens freely: enter image description here

However - the use as a user for devices for entertainment and non-formal purposes - is justified - because of different experience and feeling - this is probably the next step to more immersion experiments, correlated with 3D or VR interfaces.

enter image description here

More research:

https://www.nature.com/articles/s41528-017-0006-9 https://www.researchgate.net/publication/220876899_Foldable_interactive_displays

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