The unofficial guide to building Action Extensions

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The unoﬃcial guide to building Action Extensions

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Extensions • Set up as a separate target • Out of process of the host app or the containing app • Has its own sandbox • Can share data with the containing app through App Groups • Can share data with the host app only through XPC

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Action Extensions • Visible in the share sheet in the second row • “An Action extension helps users view or transform content originating in a host app.” [1] • On launch the extension gets the data to be shared from the host app through a NSExtensionContext [1]: https://developer.apple.com/library/content/documentation/General/Conceptual/ExtensibilityPG/Action.html

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Today’s Talk • How to implement an action extension in theory • How to make that implementation work in practice • I will not cover the host app’s integration

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The Theory

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The Loop for (NSExtensionItem *item in self.extensionContext.inputItems) {  for (NSItemProvider *prov in item.attachments) {  if ([prov hasItemConformingToTypeIdentifier:(NSString *)kUTTypeImage]){  __weak UIImageView *imageView = self.imageView;  [prov loadItemForTypeIdentifier:(NSString *)kUTTypeImage  options:nil  completionHandler:^(UIImage *image, NSError *error) {  if(image) {  [[NSOperationQueue mainQueue] addOperationWithBlock:^{  [imageView setImage:image];  }];  }  }];  }  }  }

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Modifying the Loop for (NSExtensionItem *item in self.extensionContext.inputItems) {  for (NSItemProvider *prov in item.attachments) {  if ([prov hasItemConformingToTypeIdentifier:(NSString *)kUTTypeImage]){  __weak UIImageView *imageView = self.imageView;  [prov loadItemForTypeIdentifier:(NSString *)kUTTypeImage  options:nil  completionHandler:^(NSData *data, NSError *error) {  NSURL* targetURL = …;  [data writeToURL:targetURL atomically:YES];  }];  }  }  }

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Demo

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Pitfalls • Data might come in various different formats even for the same type identifier • Some fileURLs seem to not be accessible from the sandbox • Specify the loaded item as id and look at the data you get

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Error Handling • What can go wrong, will go wrong • If you use Swift: Don’t do any force unwrapping or fatalError() calls • If you use Objective-C: Be super careful with everything that is declared nullable

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Error Handling • Sometimes your extension might even get launched but does not receive any items at all • Handle absolutely everything that could happen, from an API point of view, not from a documentation point of view • You are dealing with random apps that could do random things

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Radar Time • Safari shares images as Data, other apps as URL (rdar://29924023) • Message.app shares image ﬁle url not accessible from inside an action extension (rdar:// 29918507) • Photos.app advertises live photo to action extensions which then can't be accessed (rdar:// 29924331) • Messages.app advertises live photos to action extensions as public.image and is sharing a jpeg (rdar://29924679) • Host apps interfere with the tint color of extensions (rdar://30141950) • There needs to be a document describing the diﬀerences of NSExtensionItem, NSItemProvider and the items from an NSItemProvider (rdar://30184485)

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Radar Time • P.s.: Please ﬁle radars or dupe the ones you want to get ﬁxed!

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Radar Time • P.s.: Please ﬁle radars or dupe the ones you want to get ﬁxed!

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Radar Time • P.s.: Please ﬁle radars or dupe the ones you want to get ﬁxed!

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–Tanya Gupta, Engineering Manager at Apple “Sometimes they say, well it’s a really obvious problem! I’m sure you have 12 copies of the bug […] should I still ﬁle a bug report? Yes, you should still ﬁle a bug report. Better have 5 copies of a bug than none at all. At Apple, if an issue is not tracked using a bug report, it essentially does not exist for us.”

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Radar Time • Sample projects help you to identify the problem • Use OpenRadar if you can

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Demo

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UIAppearance • Either ensure your extension can deal with every possible appearance • Or set NSExtensionOverridesHostUIAppearance to YES in the NSExtension dictionary in the extension’s Info.plist

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Getting ready to ship • Set the activation rule in you extension’s Info.plist • TRUEPREDICATE is great for debugging

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Getting ready to ship • Set the activation rule in you extension’s Info.plist • TRUEPREDICATE is great for debugging

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Getting ready to ship SUBQUERY (  extensionItems,  $extensionItem,  SUBQUERY (  $extensionItem.attachments,  $attachment,  (ANY $attachment.registeredTypeIdentifiers UTI-CONFORMS-TO "com.adobe.pdf" OR  ANY $attachment.registeredTypeIdentifiers UTI-CONFORMS-TO "public.file-url" OR  ANY $attachment.registeredTypeIdentifiers UTI-CONFORMS-TO "public.url" OR  ANY $attachment.registeredTypeIdentifiers UTI-CONFORMS-TO "public.jpeg" OR  ANY $attachment.registeredTypeIdentifiers UTI-CONFORMS-TO "public.png" OR  ANY $attachment.registeredTypeIdentifiers UTI-CONFORMS-TO "public.image") AND  NOT (ANY $attachment.registeredTypeIdentifiers UTI-CONFORMS-TO  "com.pspdfkit.viewer.blocker")  ).@count == $extensionItem.attachments.@count  ).@count >= 1

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Reading Material • The Struggle with Action Extensions  https://pspdfkit.com/blog/2017/action-extension/ • Hiding Your Action and Share Extensions In Your Own Apps  https://pspdfkit.com/blog/2016/hiding-action-share-extensions-in-your- own-apps/ • Writing good bug reports  https://pspdfkit.com/blog/2016/writing-good-bug-reports/

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Thank you Michael Ochs @_mochs https://pspdfkit.com/blog/