Monthly Archives: September 2015

Presenting HTML On Apple TV

In a recent post on my Bitsplitting blog, I┬ácomplained┬áthat Apple’s forbiddance of web views on Apple TV would limit many developers who use HTML tastefully in the construction of their interfaces. I suggested that Apple might allow developers to use web views, but limit their usefulness as full-fledged web browsers.

Since writing that article, I discovered a potentially useful “backdoor” of sorts that could allow developers to continue using HTML to some extent for visual formatting of content in their user interfaces.

UITextView supports attributed strings, and NSAttributedString supports being initialized with HTML. Historically on the Mac at least, this capability was famously poor, but I seem to recall reading that it had been boosted at some point by using WebKit behind the scenes to do a more proper conversion.

Here’s an example of how an Apple TV app can convert literal HTML content into a visual form. This is, so far as I can tell, compliant with both the letter and the spirit of Apple’s guidelines for using the SDK:

NSString* staticHTMLContent = @"<div style='font-size:6em;'><strong>Hello</strong> <span style='font-family:courier;'>there</span>, I'm <span style='color:red;'>HTML</span>!</div>";

NSAttributedString* myHTMLString = [[NSAttributedString alloc] initWithData:[staticHTMLContent dataUsingEncoding:NSUTF8StringEncoding] options:@{NSDocumentTypeDocumentAttribute : NSHTMLTextDocumentType} documentAttributes:nil error:nil];

[self.textView setAttributedText:myHTMLString];

This example code is run from a UIViewController whose self.textView is an IBOutlet to a UITextView in the user interface. And here’s how it looks in the Apple TV simulator:

HTML rendered on the Apple TV simulator

Granted, this is a far cry from a fully-functional web view. I’m sure it won’t serve the needs of all developers who currently rely upon UIWebView or WKWebView, but I expect that in some cases it will be a valuable workaround to the otherwise total omission of support for rendering HTML on Apple TV.

Not Available On tvOS

Along with many other Mac and iOS developers, I’m digging into Apple’s SDK for tvOS development. As announced in the special event yesterday, the SDK is based on iOS and will be very familiar to most Apple platform developers. There are, however, some differences: functionality from iOS frameworks that is not available on tvOS, as well as a handful of new frameworks specifically suited to the needs of “TV apps.”

A very notable absence is UIWebView. Black Pixel’s Daniel Pasco points out on Twitter that this will be a significant impediment to porting many iOS apps:

When I say UIWebView is absent, I should clarify that the class name is still present in the UIKit headers on the tvOS SDK, but it is marked with a new compiler availability attribute, __TVOS_PROHIBITED. This is handy because at least when you run up against the problem, you don’t have to fret about whether you simply neglected to link against the right framework. It’s there, it may or may not work, you just can’t use it.

In case it’s not obvious, you can use a massive search of the SDK’s header files to zero in on other such classes and methods that may be prohibited from use in TV apps:

grep -r TVOS_PROHIBITED UIKit.framework/Headers/*

(Note: it was brought to my attention that this search is purely academic because Apple has published a browsable list of API changes from iOS to tvOS.)

The results are a doozy! But many of the marked items simply wouldn’t make sense on Apple TV, like mucking with the UIStatusBar, are marked as prohibited. There are other tags too, such as __TVOS_UNAVAILABLE, which presumably denotes that technologies that Apple would like to provide but hasn’t yet, and __TVOS_DEPRECATED, which blessedly does not yet match any API provided in the tvOS SDK.

Take a look in the Availability.h header file for this and other interesting attribute definitions, including counterparts for OSX, iOS, and watchOS.