Will they be letterboxed, as the iPhone 5 did with apps still built for the 3.5" screen, or will the phone try to adapt them to the full screen size?
How will apps built with a Base SDK of iOS 10 appear on the iPhone X?
I don't think much has changed with the principles towards the Sizing Classes & Auto layout between iOS 10 & iOS 11, you can always build an app for the sim on the device in question, locate it on disk, then drag and drop it onto the iPhone X sim and view the results.
I've heard that to "enable the iPhone X resolution" you need to build against the iOS 11 SDK, but I'm not sure if that means enabling pixel density (@3x assets, etc.) or the full height of the device, nor what happens to pre-iOS 11 SDK-built apps. The most-recent episode of Under The Radar podcast suggested there was a compatability mode that would letterbox the apps, but I'm not sure where they got this information from.
I can confirm, that if your app isn't built with the iOS 11 SDK then it will run in letterboxed compatability mode. You can see this yourself, by running the iPhone X simulator, taking an app built against the iOS 10 SDK (usually in ~/Library/Developer/Xcode/DerivedData) and then dragging it into the simulator to load it.
I've just finished getting one of my apps ready for iOS 11/iPhone X. I had to update my LaunchImage to include a size for the iPhone X. I'd imagine if you're using a Launch storyboard building with the SDK might have been enough.
What a great trick! I'd never thought to try that. It worked exactly like you said. Thanks.
Does this mean there will be a gap at the bottom of the screen if an app built against iOS10 SDK (or earlier) will be running on iPhone X?
So the new bar at the bottom of iPhone X that replaces the home button will not overlay my app content? That would be good.
Does someone has a screenshot how exactly this looks like?
Thank you so much!
Yes, the notch and new home indicator will not overlap your app, even in landscape mode.
(Note that this behavior is based on the current simulator and iOS 11.0 so could be different on an actual device, but I see no reason for it not to work this way. Apple has implemented compatibility modes before when screen sizes have dramatically changed.)