Gruber shared the tidbit in a blog post covering "scuttlebutt" he's heard about the cross-platform UI project, which he says is indeed in the works at Apple.
News of support for universal apps able to run on iPhone, iPad, and Mac was first shared by Bloomberg's Mark Gurman in December. At the time, Gurman said Apple would introduce the functionality in iOS 12 and macOS 10.14, with an announcement likely to happen at the Worldwide Developer's Conference in June.
Gurman and Axios' Ina Fried later confirmed in January that the combined app framework was on the table for 2018 despite other planned iOS 12 and macOS 10.14 features being pushed back, but Gruber says he's "nearly certain" it's a 2019 project for macOS 10.15 and iOS 13, which could also be part of an updated UI for iOS said to be coming next year. "I would set your expectations accordingly for this year's WWDC," he writes.
According to Gruber, from what he's heard through first and second-hand sources, Apple appears to be working on declarative control APIs for iOS and macOS, which suggests Apple wants to make it easy for developers to create modern cross-platform user interfaces. Gruber's info is not as definitive as outright support for cross-platform iOS and macOS apps as has been previously reported, but it is an indication that Apple is working towards that goal.
There's nothing inherently cross-platform about a declarative control API. But it makes sense that if Apple believes that (a) iOS and MacOS should have declarative control APIs, and (b) they should address the problem of abstracting the API differences between UIKit (iOS) and AppKit (MacOS), that they would tackle them at the same time. Or perhaps the logic is simply that if they're going to create a cross-platform UI framework, the basis for that framework should be a declarative user interface.It's not clear who is correct on the timing of the universal app project given the conflicting information, but we don't have long to wait to find out. macOS 10.14 and iOS 12 will be introduced at the keynote event of the Worldwide Developers Conference, which is set to take place on June 4.
Gruber's full writeup with additional details on the project can be found over at Daring Fireball.
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