Category Archives: Mac

Finder Quick Actions

In the What’s New in Cocoa for macOS session at WWDC 2018, Apple announced Quick Actions, which are handy little contextual tasks you can invoke on selected items in the Finder, either from a contextual menu or from the Preview side panel.

The emphasis in the session was on creating Quick Actions via Automator. There, it’s as simple as creating a new workflow document, selecting “Quick Action” from the template palette, and saving. It even puts it in the right place (~/Library/Services).

Essentially, Quick Actions appear to be macOS Services, which have a long history and which Automator has previously been able to create. In fact in macOS Mojave betas, the Quick Action document seems to completely supersede the “Service” type.

But what about native applications that want to provide Quick Actions? I didn’t see anything in the WWDC session to address this scenario, so I started poking around myself. When you click the “More…” button in Finder’s Preview panel, it opens up System Preferences’s Extensions settings, focused on a special “Finder” section. In the list are several built-in extensions.

I thought these were likely to be implemented as binary app extensions, so I instinctively control-clicked on one. A “Reveal in Finder” option appeared, so I selected it. Sure enough, they live inside Finder itself, and are packaged as “.appex” bundles, the same format that Apple supports for 3rd-party applications.

What’s handy about finding an example of an app extension you want to emulate, is you can open up its bundle and examine the Info.plist. Apple’s approach to identifying app extensions’s capabilities and appearance is based heavily on the specification of values in an NSExtension entry. Looking at one of Apples models, I saw confirmation that at least this variant was of type “com.apple.services” and that its attributes included many useful values. NSExtensionActivationRule, are substantially documented, and can be used to finely tune which types of target items an extension can perform useful actions on.

Others, such as NSExtensionServiceAllowsFinderPreviewItem and NSExtensionServiceFinderPreviewIconName do not appear to be publicly documented yet, but one can guess at what their meaning is. I’m not sure yet if the icon name has to be something public or if you can bundle a custom icon and reference it from the extension. I was alerted on Twitter to at least one other key: NSExtensionServiceAllowsTouchBarItem, which evidently triggers the action’s appearance in the Touch Bar while a qualified item is selected.

Dumping AppKit’s framework binary and grepping for likely matches reveals the following key values which are pretty easy to guess the meaning of:

NSExtensionServiceAllowsFinderPreviewItem
NSExtensionServiceFinderPreviewLabel
NSExtensionServiceFinderPreviewIconName
NSExtensionServiceAllowsTouchBarItem
NSExtensionServiceTouchBarLabel
NSExtensionServiceTouchBarIconName
NSExtensionServiceTouchBarBezelColorName
NSExtensionServiceToolbarPaletteLabel
NSExtensionServiceToolbarIconName
NSExtensionServiceToolbarIconFile
NSExtensionServiceAllowsToolbarItem

Of course, until these are documented, and even when they are, until macOS Mojave 10.14 ships, you should consider these all to be preliminary values which could disappear depending on further development by Apple of the upcoming OS.

Apple Events Usage Description

In case you haven’t heard, macOS Mojave is bringing a new “Apple Events sandbox” that will affect the behavior of apps that send Apple Events to other apps either directly, or by way of running an AppleScript. I wrote more about this on my non-development blog, Bitsplitting: Reauthorizing Automation in Mojave.

Typically, the system is simply supposed to ask users whether they approve of the Apple Events being sent from one app to another, but in some instances it seems the events are rejected without ever prompting the user. My friend Paul Kim of Hazel fame asked in a developer chat room whether any of us were having this kind of trouble specifically with apps built in Xcode 10, against the macOS 10.14 SDK.

This rang a bell for me on two levels: first, I had seen a similar behavior with FastScripts, which I eventually fixed by switching it to a much newer build system, and dropping support for versions of macOS older than 10.12. It was the right time for me to make those changes, so I didn’t mind doing it, but I never quite understood why the behavior was happening.

I noticed after building and running on my developer Mac (which is running the 10.14 beta), I was still experiencing the behavior Paul described. With FastScripts, these kinds of alerts pop up all over the place, because by virtue of running scripts, users are often incidentally sending Apple Events to other apps. Here’s a simple example script that I can run via FastScripts:

tell app "Preview"
    get document 1
end tell

When I run this with a version of FastScripts that was linked against the 10.14 SDK, I get this error message from FastScripts itself. The system never prompts to grant permission:

Scripting error received when attempting to run a script from FastScripts

Until Paul mentioned his own problems, I glossed over these failures because I was satisfied that my production built versions, linked against the 10.13 SDK, were “working fine.” But Paul’s report got me thinking: was it possible there is some unspoken contract here, whereby linking against the 10.14 SDK opens up my app to additional privacy related requirements?

I tapped into Xcode’s Info.plist editor for FastScripts, added a new field, and typed “Privacy” on a hunch, because I’ve come to realize that Apple prefixes the plain-English description for most, if not all, of their “usage explanation” Info.plist fields with this word:

Screenshot of the list of Privacy-related Info.plist strings that appears

Aha, that first one looks promising. You can right-click on an Info.plist string in Xcode to “Show Raw Keys/Values”, and doing so reveals that the Info.plist key in question is “NSAppleEventsUsageDescription”. After adding the key to my app, I built and run again, and running the same script as above now yields the expected authorization panel:

Screenshot of Apple's standard panel requesting access for FastScripts to control another app.

I’m not sure if requiring the usage description string is intentional or not, but it’s probably a good idea even if, as in the case of FastScripts, you have to be pretty vague about what the specific usage is. I don’t think this usage string was covered in the WWDC 2018 session about macOS security. Hopefully if you’ve run into this with your Mac app, this post will help you to work around the problem.

Let it Rip

In the latest Mojave public beta, I noticed a foreboding warning in the console when I build and run FastScripts, my macOS scripting utility:

FastScripts [...] is calling TIS/TSM in non-main thread environment, ERROR : This is NOT allowed. Please call TIS/TSM in main thread!!!

Ruh-roh, that doesn’t sound good. Particularly with the emphasis of three, count them three, exclamation points! I better figure out what’s going on here. But how?

Sometimes when Apple adds a log message like this, they are kind enough to offer advice about what to do to alleviate the problem. Sometimes the advice implores that we stop using a deprecated method, or in a scenario like this, offers a symbolic breakpoint we might set to zero in on exactly where the offending code lies. For example, a quick survey of my open Console app reveals:

default	11:54:18.482226 -0400	com.apple.WebKit.WebContent	Set a breakpoint at SLSLogBreak to catch errors/faults as they are logged.

This particular warning doesn’t seem to apply to my app, but if it did, I would have something good to go on if I wanted to learn more. With the TIS/TSM warning, however, I have no idea where to go. Do I even use TIS/TSM? What is TSM?

I’ve worked on Apple platforms for long enough to know that TSM stands for Text Services Manager. However, I have also worked on these platforms long enough to forget whether I’ve actually used, or am still using, such a framework in my apps! When these kinds of warnings appear in the console, as many times as not they reflect imperfections in Apple’s own framework code. Is it something Apple’s doing, or something I’m doing, that’s triggering this message?

Ideally we could set a breakpoint on the very line of code that causes this console message to be printed. This can be surprisingly difficult though. There have always been a variety of logging mechanisms. Should you set the breakpoint on NSLog, os_log, printf, fprintf, or write? I could probably figure out a comprehensive method for catching anything that might write to the console, but am I even sure this console method is being generated in my app’s main process? There are a lot of variables here. (Hah! In this particular case, I ended up digging deeper and discovering it calls “CFLog”).

This is a scenario where combining lldb’s powerful “regular expression breakpoints” and “breakpoint commands” can help a great deal. Early in my app’s launch, before the warning messages are logged, I break in lldb and add a breakpoint:

(lldb) break set -r TIS|TSM.*

I’m banking on the likelihood that whatever function is leading to this warning contains the pertinent framework prefixes. It turns out to be a good bet:

Breakpoint 5: 634 locations.

I hit continue and let my app continue launching. Here’s the problem, though: those 634 breakpoint locations include quite a few that are getting hit on a regular basis, and for several consecutive breaks, none of them is triggering the warning message I’m concerned about. This is a situation where I prefer to “let it rip” and sort out the details later:

(lldb) break command add 5
Enter your debugger command(s).  Type 'DONE' to end.
> bt
> c
> DONE
(lldb) c
Process 16022 resuming

What this does is add a series of commands that will be run automatically by lldb whenever breakpoint 5 (the one I just set) is hit. This applies to any of the 634 locations that are associated with the regular expression I provided. When the breakpoint is hit, it will first invoke the “bt” command to print a backtrace of all the calls leading up to this call, and then it will invoke the “continue” command to keep running the app. After the app has run for a bit, I search the debugger console for “!!!” which I remembered from the original warning. Locating it, I simply scroll up to see the backtrace command that had most recently been invoked:

  thread #7, stop reason = breakpoint 5.568
    frame #0: 0x00007fff2cd520fd HIToolbox`TSMGetInputSourceProperty
    frame #1: 0x00000001003faef2 RSFoundation`-[RSKeyboardStatus update](self=0x00006000002b8c00, _cmd="update") at RSKeyboardStatus.m:56
    [...]

Command #2 'c' continued the target.
2018-08-14 12:15:40.326538-0400 FastScripts[16022:624168] pid(16022)/euid(501) is calling TIS/TSM in non-main thread environment, ERROR : This is NOT allowed. Please call TIS/TSM in main thread!!! 

Sure enough, that’s my code. I’m calling TSM framework functions to handle key translation for FastScripts’s keyboard shortcut functionality, and I’m doing it (gasp!) from thread #7, which is certainly not the main thread. I oughta be ashamed…

But I’m proud, because I tracked down the root of the problem pretty efficiently using lldb’s fantastic breakpoint commands. Next time you’re at a loss for how or where something could possibly be happening, consider the possibility of setting a broad, regular expression based breakpoint, and a series of commands to help clarify what’s happening when those breakpoints are hit. Then? Let it rip!

Getting a CFNumber’s Value in Swift

Recently, as a consequence of working with the CGImageSource API, I found myself in a situation where I had hold of a CFNumber and wanted to get its value, as a CGFloat, in Swift.

CFNumber wraps numeric values in such a way that, to get the value out, you have to specify both the desired type, and provide a pointer to the memory of the variable that will hold the value. This kind of direct memory manipulation is not particularly suited to Swift’s priorities for type safety and memory protection. Here’s the API I’d need to use in Swift:

func CFNumberGetValue(_ number: CFNumber!, 
                    _ theType: CFNumberType, 
                    _ valuePtr: UnsafeMutableRawPointer!) -> Bool

The first two parameters are straightforward, but whenever I see types like “UnsafeMutableRawPointer” in Swift, my brain melts down a little. I have never really sat down to truly understand the nuanced differences between these types, so I usually just try something and hope it works. Here I am hoping for a gift from Swift’s implicit bridging:

// myCFNumber is 30.5
var myFloat: CGFloat = 0
CFNumberGetValue(myCFNumber, .floatType, &myFloat)
print(myFloat) // "5.46688490824244e-315\n"

Welp. That didn’t work. Let’s see if we can refresh our memory about UnsafeMutableRawPointer. In the section titled “Raw, Unitialized Memory” or I read:

You can use methods like initializeMemory(as:from:) and moveInitializeMemory(as:from:count:) to bind raw memory to a type and initialize it with a value or series of values.

Oh jeez, am I really going to have to manually create an UnsafeMutableRawPointer? I’ll try anything:

var myFloat: CGFloat = 0
var myFloatPointer = UnsafeMutableRawPointer(mutating: &myFloat)
CFNumberGetValue(myCFNumber, .floatType, myFloatPointer)
print(myFloat) // "5.46688490824244e-315\n"

Alas, same problem. Surely somebody has figured this out? I try Googling for “CFNumberGetValue Swift GitHub” and find a promising result from an authoritative source. The Swift standard library itself!

var value: Float = 0
CFNumberGetValue(_cfObject, kCFNumberFloatType, &value)

Aha! Practically the same thing I was doing, except for one nuanced detail: the var value is declared as a Float instead of a CGFloat. But wait a minute, what file is this implementation in? NSNumber.swift? Oh, right. NSNumber and CFNumber are toll-free bridged, and Swift’s standard library fulfills that promise too:

let myFloat = (myCFNumber as NSNumber).floatValue
print(myFloat) // 30.5

In fact, Swift’s Float type is even cozier with CFNumber than I expected. What started as a confused mission to make use of CFNumberGetValue and its unsafe pointer argument culminated in a bit of sample code from GitHub that ultimately led me to the understanding that the way to get a CFNumber’s value in Swift is … simply to ask for it:

let myFloat = Float(myCFNumber)
print(myFloat) // 30.5

Helpless Help Menu

I was alerted by Christian Tietze of a pretty bad usability bug in macOS High Sierra. If you are running a Mac app, click the “Help” menu, and then dismiss it, whatever UI element you were focused on in the app loses its focus and does not regain it after dismissing the menu.

The problem is so bad that tabbing, clicking other UI elements, even switching to another app and back does not restore focus on the window’s responders. If the focus was on an NSTextView, such as the editor in MarsEdit, then the blinking cursor continues to animate, but keystrokes are ignored and simply cause the app to beep.

Christian filed a bug, and shared a workaround: set the delegate of the Help menu to your app’s delegate, and listen for the “menuDidClose” delegate method. If it’s the Help menu, restore focus manually.

I generalized this workaround to an approach that should work for whatever window, and whatever responder is currently focused when the Help menu is opened. By saving the window and the responder at “menuWillOpen” time, it can be precisely restored afterwards:

private weak var lastKeyWindow: NSWindow? = nil
private weak var lastResponder: NSResponder? = nil

func menuWillOpen(_ menu: NSMenu) {
   if menu == NSApp.helpMenu {
      if let activeWindow = NSApp.keyWindow {
         self.lastKeyWindow = activeWindow

         if let activeResponder = activeWindow.firstResponder {
            self.lastResponder = activeResponder
         }
      }

      // If the responder is a field editor, then save 
      // the delegate, which is e.g. the NSTextField being edited,
      // rather than the ephemeral NSTextView which will be 
      // removed when editing stops.
      if let textView = lastResponder as? NSTextView,
         textView.isFieldEditor {
         if let realTarget = textView.delegate as? NSResponder {
            lastResponder = realTarget
         }
      }
   }
}

func menuDidClose(_ menu: NSMenu) {
   if menu == NSApp.helpMenu {
      if doWorkaround {
         if let actualKeyWindow = self.lastKeyWindow {
            actualKeyWindow.makeKeyAndOrderFront(nil)
            actualKeyWindow.makeFirstResponder(self.lastResponder)
         }
      }
   }
}

Note that I didn’t clear out the weak var references to the lastKeyWindow and lastResponder. The reason is because part of the bug here involved NSMenu’s menuWillOpen and menuDidClose getting called more often than they probably should be. It’s probably the root issues that is causing the Help menu to excessively take control of the key window. It turns out we are going to get called on menuDidClose twice, so we need to be sure the desired target window and responder are still available the second time around.

As Christian points out, the workaround fixes the worst aspect of the bug: locking up the UI so that typing is ignored, but the focus ring around the target text field doesn’t always get redrawn as expected. My theory is that the focus ring animation is in the process of drawing when the second “menu will open” event is generated, causing the Help menu to reactive itself. The field being reactivate again very shortly after somehow doesn’t trigger the need to redraw the focus ring as you might expect.

I filed an additional bug, Radar #39436005, including a sample project that demonstrates both the bug and the workaround. Until Apple fixes this, Mac developers may want to implement a workaround along the lines demonstrated here. Given the horrible user experience associated with this bug, hopefully Apple will fix it promptly!

Swift Integration Traps

In the nearly four years since Swift was announced at WWDC 2014, Mac and iOS developers have embraced the language with decreasing reluctance. As language features evolve, syntax stabilizes, and tooling improves, it’s easier than ever to leap into full-fledged Swift development.

Several months ago, I myself made this leap. Although the vast majority of my Mac source base consists of Objective-C files, I have enjoyed adding new source files in Swift, and even converting key files to Swift either as an exercise, or when I think I will gain specific advantages.

One remaining challenge in Swift is the lack of ABI stability. In layperson’s terms: the lack of ABI stability prevents compiled Swift code from one version of the Swift compiler and runtime from linking with and running in tandem with Swift code compiled for another version.

For most developers, this limitation simply means that the entire Swift standard library, along with glue libraries for linking to system frameworks, needs to be bundled with the application that is built with Swift. Although it’s a nuisance that several megabytes of libraries must be added to every single Swift app, in the big scheme of things, it’s not a big deal.

A worse consequence is the number of pitfalls that ABI instability present, that are difficult to understand intuitively, and in many cases impossible, or at least dangerous, to work around. These pitfalls lie mainly in areas where developer code is executed on behalf of a system service, in a system process. In this context, it is not possible for developers to ensure that the required version of Swift libraries will be available to support their code. Game over.

On the Mac, system integration plugins are a typical scenario for this problem. While iOS has evolved with a strong architecture for running developer code in standalone, sandboxed processes, on the Mac there are still many plugins that run in a shared system process alongside code from other developers. These plugins run the gamut from arcane, rarely used functionality, to very common, user-facing features where a plugin is effectively required in order to satisfy the platform behaviors prescribed by Apple and expected by end-users.

One example on the more arcane, or at least inessential, end of the spectrum, is the Screen Saver plugin interface. Create a new project in Xcode, and choose the “Screen Saver Plugin” template as your starting point. Notice how unlike most templates, Xcode doesn’t even offer a choice of language. Your source files will be Objective-C. At least they’re giving you a hint here.

On the more mainstream end of the spectrum are plugins such as System Preferences panels and QuickLook Plugins. Depending on the type of app you are developing, it may be essential, or at least very well-advised to implement one of these types of plugins. So what do you do if you have an existing Objective-C app that you want to port to Swift, or you are writing a Swift app from scratch, and need to support one of these plugin formats? In the case of System Preferences panels at least, you have a couple practical options:

  1. Implement the plugin code, and all supporting code in Objective-C.
  2. Move the functionality out of System Preferences and into the host app.

Each of these could be somewhat reasonable approaches for a System Preferences plugin. The content of these plugins is often fairly straightforward, standard UI, and the goal is usually to collect configuration data to convey to the host application. It’s also not unreasonable, and may even be preferable to move such configuration code out of System Preferences and into a native panel inside the host app.

QuickLook Plugins are another beast. Because the goal of a QuickLook Plugin is usually to convey a visual depiction of a native document type, it’s exceedingly common to take advantage of the very classes that present the document natively in the host app. Let’s say you’ve written an app in Swift, FancyGraphMaker. Apple encourages you to implement a QuickLook Plugin so that users will be able preview the appearance of your fancy graphs, both in the dedicated QuickLook interface, and by way of more unique looking icons in the Finder.

But once you’ve written the code to draw those fancy graphs in Swift, you’re locked out of using that code from a QuickLook Plugin. Worse? Finishing touches such as supporting Quick Look are liable to come later in the development of an app, so you’ve probably gone through the decision-making process of writing your app in Swift, before realizing that the decision effectively cuts you off from a key system feature. That’s a Swift Integration Trap.

Although the workarounds are not as straight-forward in this scenario as they are for a System Preferences pane, it is probably still technically possible to leverage Swift code in the implementation of a QuickLook Plugin. I have not tested this, but I imagine such a plugin could spawn an XPC process that is itself implemented in Swift and executes the bulk of the preview-generation work on behalf of the system-encumbered plugin code. The XPC process would be free to link to whatever bundled Swift libraries it requires, generate the desired preview data, and message it back to the host process. At least, I think that would work.

But I shouldn’t have to think that hard to get this to work, nor should any other developer. The problem with these Swift Integration Traps is twofold:

  1. If you don’t know about them, you end up stuck, potentially regretting the decision to move to Swift.
  2. If you do know about them, you might put off adopting Swift completely, or at least put off converting classes that are pertinent to QuickLook preview generation.

Each of these consequences is bad for developers, for users, and for Apple. Developers face a trickier decision process about whether to move to Swift, users face potential integration shortcomings for Swift-based apps, and Apple suffers either reduced adoption of Swift, reduced integration with system services, or both.

I filed Radar #38792518 requesting that QuickLook Plugins be supported by the App Extension model. Essentially, this would formalize the process of putting the generation code in a separate XPC process, as I speculated above would work around the problem. The App Extension system is designed to support, and in fact requires this approach. The faster Apple moves QuickLook Plugins, and other shared-process plugins to the App Extension model, the fast developers can embrace Swift with full knowledge that their efforts to integrate with the system will not be stymied.

Update: Thanks to a hint from Chris Liscio, I have learned that Apple has in fact made some progress on the QuickLook front, but it won’t help the vast majority of cases in which a QuickLook Plugin is used to provide previews for custom file types. It took me a while to hunt this down because it not very clearly documented, and Google searches do not lead to information about it.

At WWDC 2017, Apple announced support for a new QuickLook Preview Extension. It escaped my notice even while ardently searching for evidence of such a beast, because the news was shared in the What’s New in Core Spotlight session. Making matters worse, the term “QuickLook” does not appear once in the session transcript, although it turns out that “Quick Look” appears many times:

Core Spotlight is also coming to macOS and just like on iOS you can customize your preview. On macOS a preview is shown when you select a search result in the Spotlight window. Here you really do want to implement a Quick Look preview extension for your Core Spotlight item because Spotlight on macOS does not have a default preview.

Ooh, this sounds exciting! I’ve wondered over the years why such similar plugins, Spotlight importers, and QuickLook generators, shouldn’t be unified. Although the WWDC presentation emphasizes substantial parity in behavior for QuickLook Previews between iOS and macOS, there is a major gotcha:

Core Spotlight is great for databases and shoeboxes where your app has full control over the contents.
It’s not for items that the user monitors in the finder, for that the classic Spotlight API still exists and still works great.

I beg to differ with that “still works great” assessment, at least in the context of this post. Mac developers who want to integrate with QuickLook must still use a shared-process plugin. It’s still a Swift Integration Trap.

IDEBundleInjection Signing Failure

When a unit test bundle is built to be dynamically injected into a host app, Xcode performs a little dance at build time, in which it adds its own IDEBundleInjection.framework to the bundle, then re-signs it with the developer’s code signing identity.

Normally this all goes off without a hitch, but today when I went to build and test such a bundle, I was met with a rude code signing failure:

IDEBundleInjection.framework: unsealed contents present in the root directory of an embedded framework

I took all the usual steps when facing an obtuse error: clean the build directory, quit and restart Xcode, etc. Nothing fixed it, so I thought perhaps it was an issue with the 9.3 beta Xcode I was running. Nope. Same problem with 9.2. Finally, I made my own copy of the framework in question, and ran “codesign” against it myself from the Terminal. Same error!

This framework, stored within Xcode itself, has become unsignable. Running “codesign -v” against the framework in place also confirms that the code signing seal has been broken. What happened to my Xcode?

It occurred to me that I recently migrated from one Mac to another, and copied my Xcode when I did. I tried to use the Apple-standard migration assistant, but it failed, so I ended up using Finder, or ditto from the Terminal, to copy everything over. Maybe something was messed up in the transition?

The codesign utility is useful for letting me know that something is wrong, but doesn’t actually do me the favor of telling me what it is! Luckily, I have a backup of my whole disk and the original Xcode on that volume appear to have properly signed internal frameworks. Running a diff on IDEBundleInjection.framework between the two copies, I do see some reported distinctions. Where “.” is the current, misbehaving framework:

Only in .: .BC.D_QdfhyO
Only in .: .BC.D_mgLUu2
Only in ./Versions: .BC.D_gSVCxT

These appear to be redundant cruft correlating to the expected internal version links. For every link like:

IDEBundleInjection -> Versions/Current/IDEBundleInjection

I have one of these unexpected garbage links. The presence of these links are, of course, detected by codesign, and it throws everything off.

I don’t know why these mysterious gremlin files showed up on my Mac, but whatever the cause, there’s an easy solution. I’m taking a leap of faith that I don’t actually want any of these files:

cd /Applications/Xcode.app
find . -name ".BC.*" -delete

And now I can get back to unit testing my app.

Accessible Frames

I love the macOS system-wide dictionary lookup feature. If you’re not familiar with this, just hold down the Control, Command, and D keys while hovering with the mouse cursor over a word, and the definition appears. What’s amazing about this feature is it works virtually everwyhere on the system, even in apps where the developers made no special effort to support it.

Occasionally, while solving a crossword puzzle in my own Black Ink app, I use this functionality to shed some light on one of the words in a clue. As alluded to above, it “just works” without any special work on my part:

Screen shot of Black Ink's interface, with a highlighted word being defined by macOS system-wide dictionary lookup.

Look carefully at the screenshot above, and you can see that although the dictionary definition for “Smidgen” appears, it seems to have highlighted the word in the wrong location. What’s going on here?

The view in Black Ink that displays the word is a custom NSTextField subclass called RSAutosizingTextField. It employs a custom NSTextFieldCell subclass in order to automatically adjust the font size and display position to best “fill up” the available space. In short: it behaves a lot like UITextField on iOS.

To achieve this behavior, one of the things my custom cell does is override NSTextFieldCell’s drawingRect(forBounds:). This allows me to take advantage of most of NSTextField’s default drawing behavior, but to nudge things a bit as I see fit. It’s this mix of customized and default behaviors that leads to the drawing bug seen above. I’ve overridden the drawing location, but haven’t done anything to override the content hierarchy as it’s reflected by the accessibility frameworks.

What do the accessibility frameworks have to do with macOS system-wide dictionary lookup? A lot. Apparently it’s the “accessibilityFrame” property that dictates not only where the dictionary lookup’s highlighting will be drawn, but also whether the mouse will even be considered “on top of” a visible word or not. So in the screenshot above, if the mouse is hovering over the lower half of the word “Smidgen”, then the dictionary lookup doesn’t even work.

The fix is to add an override to NSTextField’s accessibilityFrame method:

public override func accessibilityFrame() -> NSRect {
	let parentFrame = super.accessibilityFrame()
	guard let autosizingCell = self.cell as? RSAutosizingTextFieldCell else { return parentFrame }

	let horizontalOffset = autosizingCell.horizontalAdjustment(for: parentFrame)

	// If we're flipped (likely for NSTextField, then the adjustments will be inverted from what we
	// want them to be for the screen coordinates this method returns.
	let flippedMultiplier = self.isFlipped ? -1.0 as CGFloat : 1.0 as CGFloat
	let verticalOffset = flippedMultiplier * autosizingCell.verticalAdjustment(for: parentFrame)

	return NSMakeRect(parentFrame.origin.x + horizontalOffset, parentFrame.origin.y + verticalOffset, parentFrame.width, parentFrame.height)
}

Effectively I take the default accessibility frame, and nudge it by the same amount that my custom autosizing text cell is nudging the content during drawing. The result is only subtly difference, but makes a nice visual refinement, and a big improvement to usability:

Screen shot of dictionary lookup UI with properly aligned word focus.

I thought this was an interesting example of the accessibility frameworks being leveraged to provide a service that benefits a very wide spectrum of Mac users. There’s a conventional wisdom about accessibility that emphasizing the accessibility of apps will make the app more usable specifically for users who take advantage of screen readers and other accommodations, but more generally for everybody who uses the app. This is a pretty powerful example of that being the case!

Playground Graphs

I was playing around with the Swift standard library’s “map” function, when I noticed a cool feature of Xcode Playgrounds. Suppose you are working with an array of numbers. In the Xcode Playgrounds “results” section, you can either click the Quick Look “eye” icon, or click the little results rectangle to get an inline results view of the expression you’re viewing:

Screenshot of Xcode Playgrounds's inline results view, revealing the values of an array of numb ers.

The linear list of values is revelatory and easy to read, but wouldn’t it be easier to understand as a graph? It turns out simply passing these values through the map function does just that:

Screenshot of the Xcode Playgrounds's result of the map function when returning numeric values.

I thought I had stumbled on some magical secret of Xcode, but it turns out the behavior is well documented, and applies to more than just the “map” function. You can even grab the edges of the result view and resize it to better suit your data. In fact, any looping numeric value seems to trigger the availability of this handy graphing functionality:

Screenshot of Xcode Playgrounds showing a graph of the results of Fibonacci sequence.

I am still frustrated by a lot of behaviors of Xcode Playgrounds, but little gems like these are nice to stumble upon.

Swatch Your Step

Shortly after macOS 10.13 was released, I received an oddly specific bug report from a customer, who observed that the little square “swatches” in the standard Mac color panel no longer had any effect on MarsEdit’s rich text editor.

Screenshot of the macOS standard color panel.

I was able to reproduce the problem in the shipping 3.7.11 version of MarsEdit, which for various reasons is still built using an older version of Xcode, against the 10.6 SDK. The MarsEdit 4 Beta, which is built against the 10.12 SDK, does not exhibit the problem.

It’s not unusual for the behavior of Apple’s frameworks to vary based on the version of SDK an application was built against. The idea is usually to preserve the old behaviors of frameworks, so that any changes do not defy the expectations of a developer who has not been able to build and test their app against a later SDK. Sometimes, the variations in behavior lead to bugs like this one.

Using a totally straightforward demo app, consisting only of an NSTextView and a button to bring up the color panel, I was able to confirm that the bug affects an app that links against the macOS 10.9 SDK, but does not affect an app that links against the 10.10 SDK.

I filed Radar #34757710: “NSColorPanel swatches don’t work on apps linked against 10.9 or earlier.” I don’t know of a workaround yet, other than compiling against a later SDK.