How To: Detect Force Touch-Capable Devices on the Mac

In an effort to show preferences for configuring Force Touch in my apps (in particular, Yoink) only when a Force Touch device is actually available, I had to find a way to figure out how to detect Force Touch devices.

If this was iOS, I’d be done by now

On iOS, Apple provides a simple API for this:

UIForceTouchCapabilityUnavailable and UIForceTouchCapabilityAvailable

which you can check by calling UIView’s – (UIForceTouchCapability)traitCollection;. Lo and behold, a simple API like this is sadly not available on OS X. On the Mac, you have to do it yourself.

IOKit is where it’s at

Using IOKit, you can sort of set up a set of properties you’re looking for in a device and see if it returns anything. This does not only include an external or internal keyboard, mouse or trackpad, but also graphic cards, for example. To find out what the right properties are, I downloaded Apple’s Hardware IO Tools for Xcode 7.1 from their developer downloads site (Apple Developer account required) and launched the app IORegistryExplorer.

Digging down the IO Registry

I do have a Magic Trackpad 2 “attached” to my Mac via Bluetooth, so I tried searching for the term “Trackpad”, and sure enough, I saw my internal and external ones:

IORegistry TrackpadsThe Trackpads attached to my Mac, either via Bluetooth or internally.

Having found the Magic Trackpad 2, the next step is to see what properties it offers and if they are unique to the class of the device:

Trackpad PropertiesJackpot!

Sure enough, there it is – ForceSupported: True. I could not find such a key in the internal trackpad’s properties, hinting that it might be exclusive to devices that do support Force Touch. There’s also an entry for “Manufacturer”, which is “Apple Inc.”. Perfect.

Looking for Devices with IOKit

Now all I have to do is filtering devices by the Manufacturer – “Apple Inc.” -, iterate over the resulting devices, and filter out devices that have a DefaultMultitouchProperties key, containing a ForceSupported key with a value of true. If such a device is found, it means a device with Force Touch capabilities is available.

Code Listing #1

In this method, I create a dictionary mDict that is used to find matching devices. In this case, I’m looking for devices with the Manufacturer set to “Apple Inc.”. I query for possible devices using IOServiceGetMatchingServices. I can then iterate over the returned io_iterator_t iterator and recursively over the children in the core of all of this: – (BOOL)_containsForceTouchDevice:io_iterator_t)iterator;.

Code Listing #2

Here, we iterate recursively over iterator’s objects, checking for the DefaultMultitouchProperties key and, subsequently the ForceSupported key (and value).

Testing it with other Trackpads

The code you see above is final. However, in a previous version, all I could use to test it with was my Magic Trackpad 2 – an internal Force Touch Trackpad (the likes of which the new MacBooks and MacBook Pros feature) was not available to me directly. So I sent the first draft of the code to my friend (and fellow developer) Maurice Kelly (@mauricerkelly on twitter) who was kind enough to volunteer as my “test subject”; and – of course – it didn’t work. Turns out I shouldn’t assume the vendorID to be the same (which I used in the first draft just like the Manufacturer to filter the possible results). After leaving it out, it worked fine over all currently available Force Touch Trackpads.

Hot (Un-)Plugging

Sometimes you might want to get notified when devices are plugged in to or unplugged from the Mac. In Yoink, I’d like to display preferences specific to Force Touch if according hardware is available, but not show them if there isn’t any hardware connected that supports it. Also, as a nice touch, I’d like to hide the preferences if according hardware is disconnected and show it again when it is connected. We can accomplish this like that:

Code Listing #3

Sandbox

The code works just as well in the Sandbox environment, these entitlements have to be set, though, for the notifications to work:

Sandbox Entitlements

com.apple.security.device.usb and com.apple.security.device.bluetooth

Future Proof?

I’m not sure this code is future proof. The basic APIs will stay around, sure, but it all depends on the keys DefaultMultitouchProperties, ForceSupported and their according values which are not defined in the IOKit header files, which I unsuccessfully searched for constants pertaining to force/pressure. So, depending on this, the code might break with future versions of the Force Touch Trackpad and I’ll have to keep testing it as Apple releases new hardware. Nevertheless, I’m quite happy with the code and it works very well.

Getting the Source Code

I’ve uploaded a sample project to my server, you can download it here. The category on NSApplication in which this is available can be downloaded from Github. The example app is pretty simple:

Force Touch Device Detection Example App Screenshot

At launch, it asks if a Force Touch capable device is available and displays an according message. If subsequently the availability status changes, the message will be updated accordingly.

If you’d like to get in touch, you can mail me or write me on twitter. I’m looking forward to hearing from you :)

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How To Receive Force Touch Events from an NSTableView

After having spent over a (completely fruitless) month on fiddling with this without having an actual Force Touch Trackpad to test with, having gotten one recently, it still was insanely difficult for me to finally figure out how to receive Force Touch events from an NSTableView. But I finally did it. Here’s how.

Apple Keynote - MacBook Force TouchImage Credit: Apple, Inc.

The Premise

In Yoink, the usual way to select all files (pressing ⌘-A like you would in almost any application) is not a viable option. Yoink is written to not have key focus, as it would otherwise interfere with work in other applications too much (believe me, I’ve tried).
So I had to come up with a different way to do it. What I’ve done up until now is to allow the user to hold down the option (⌥) key on the keyboard and double-clicking onto any file in Yoink to select all files.

When Force Touch was introduced, I thought that would be a very nice alternative to option-double-clicking. And it is. Once I got it working, anyway.

The Issue

What I thought would be the easiest way to get Force Touch events from an NSTableView was to override – (void)pressureChangeWithEvent:(NSEvent *)theEvent.
Only that it doesn’t get called as it would normally be called: continuously, after – (void)mouseDown:(NSEvent *)theEvent, with every change of pressure on the trackpad.

No, in an NSView-based NSTableView (I haven’t tested cell-based tableViews), -pressureChangeWithEvent: gets called at -mouseDown: with a pressure of 0.0, and then just “dies”, not getting called again until the next -mouseDown:.
That’s interesting. And there’s more interesting-ness going on.

Once I override the tableView’s -mouseDown:, -pressureChangeWithEvent: suddenly gets called continuously, as you’d expect. So something apparently happens inside the tableView’s -mouseDown: implementation that sort of prevents -pressureChangeWithEvent: from getting called.

Finding A Solution

Knowing that the table view’s default implementation of -mouseDown: somehow interferes with the easy way of using -pressureChangeWithEvent:, my first attempt at a solution was to override -mouseDown: and re-implement its functionality myself, because then I would receive -pressureChangeWithEvent: properly. Then it dawned on me what I was in for. Dragging something out of the tableView (something kind of essential in Yoink) suddenly didn’t work anymore. I’d have to re-implement the selection mechanism (selecting with a mouse click, de-selecting with the command key pressed, adding an additional selection with either the shift- or the command key, etc.)
That alone would have taken more time than the entire feature of having force-click-to-select-all is worth.

Next, I thought NSGestureRecognizer could work. I created a subclass of it that overrides -pressureChangeWithEvent: and checked to see if it was called. But it was the same thing all over again. Adding it to the tableView, the NSTableRowView, the NSTableCellView and the underlying contentView of NSWindow, trying to figure out if they maybe swallowed the method call yielded no result or any change. It was all the same. It got called at the first -mouseDown: call, but then stopped.

Next I tried a local NSEvent monitor thinking it might do the trick, and it works, but only when the window’s contentView is force clicked, not the tableView. A global monitor doesn’t seem to work with pressure events.

So the only way that seemed to get me anywhere at all was to override NSTableView’s -mouseDown:. And that’s what I ended up doing. At first. After a day’s work, though, it still didn’t yield any results what-so-ever. The amount of time I’ve wasted on this is astounding, but apparently, when you keep going and really want to get somewhere, you eventually will.

The Solution

In OS X 10.10 Yosemite, Apple introduced a new NSEvent-tracking API in NSWindow: – (void)trackEventsMatchingMask:(NSEventMask)mask timeout:(NSTimeInterval)timeout mode:(NSString *)mode handler:(void(^)(NSEvent *event, BOOL *stop))trackingHandler that lets you, in a tracking loop, monitor for events matching the mask you provide, in this case, NSEventMaskPressure.

I actually had played around with this before, coming recommended from Markus Müller (@fafner on twitter), developer of the marvellous Mac and iOS app MindNode, who, by the way, in order for me to be able to test this stuff before I got my own Force Touch-able Trackpad, kindly invited me to their office to use his MacBook – thank you, Markus.
However, I didn’t get very far, as I didn’t know how to use the API correctly. Calling it from – (void)awakeFromNib, for example, isn’t the best idea, as it a) doesn’t appear to be able to track anything and b) locks up the app. It has to be called from inside a tracking loop (like -mouseDown: or -pressureChangeWithEvent:).

Again, after a lot of time wasted getting nowhere, this is the solution I came up with:

Source Code for how to receive Force Touch events from an NSTableView

I decided to imitate NSTableView’s -action and -doubleAction methods for handling receiving force touch events in a target.
NSTableView can be set up with a -target that should receive the selectors set in -action-doubleAction, and with this, -forceTouchAction, as seen in the code above, uses the same approach – send the specified selector to the NSTableView’s -target.

This code starts tracking Pressure-, Drag- and Mouse Up events in -pressureChangeWithEvent:, and practically waits until the Pressure event’s stage 2 is reached, which is a force touch. Then it sends the -forceTouchAction to -target.

The important lesson that I learned here is that the events have to be forwarded to the window, as they’re intercepted. So calling [self.window postEvent:event atStart:NO]; is imperative.

I watch for NSLeftMouseUp and NSLeftMouseDragged because I need to be able to stop tracking at some point, and mouseUp and mouseDragged are the perfect moments to do that.

Sample Project

I’ve uploaded a quick sample project to my server which you can download here. It requires OS X 10.10.3 (because of the APIs used). I’ve only tested it On 10.11 El Capitan, though, so your mileage may vary.

I hope this sample code is useful to you and saves you all the headaches I’ve experienced (and a lot of time) figuring this stuff out. Maybe I’m not smart enough. Or maybe this is harder than it should be. I dream of a time where the Force Touch APIs on OS X get the loving treatment 3D Touch enjoys on iOS ;)

How To: Animate a determinate NSProgressIndicator (Open Source)

I’m not sure if I’m imagining things, but I believe at some point before OS X Yosemite, a determinate NSProgressIndicator was able to animate to its new doubleValue, not just “jump” to it.

In an effort to have that animation again, I wrote a little category on NSProgressIndicator that does exactly that, using NSAnimation.

Progress bar animation using ESSProgressIndicatorCategory

NSProgressIndicator and Animation

NSProgressIndicator has a method called -startAnimation:. However, as the documentation states, this has no effect on determinate progress indicators.
Calling progressIndicator.animator.doubleValue = 5.0; doesn’t animate either. So with options that come with the class, we’re stuck.

As I try not to reinvent the wheel for something that’s already solved, I did some googling around, but that didn’t yield any results, either.
What became clear, though, was that there’s a lot of confusion about what -startAnimation: actually does.

NSProgressIndicator+ESSProgressIndicatorCategory

Not finding a solution on the internet, I decided to write my own, as I figured it wouldn’t take a lot of time (it didn’t).

I definitely didn’t want to subclass NSProgressIndicator and override any drawing methods.
That would have a) taken an unjustified amount of time and b) been a huge pain in the neck for sure.

The solution to me then was to use NSAnimation.

The goal was to have one method to call that sets the new doubleValue and animates to it nicely:

New method to animate a progress indicator's doubleValueThe category’s – (void)animateToDoubleValue: method

It calls a subclass of NSAnimation named ESSProgressBarAnimation with the new value and starts the animation.

initialization of the NSAnimation subclassInitializing the NSAnimation subclass ESSProgressBarAnimation

We save the original doubleValue of the progressindicator, set the duration and animationCurve and set the animation’s animationBlockingMode to NSAnimationNonBlockingThreaded so that when there’s a mouse event, for example, the animation doesn’t stop.

NSAnimation's setCurrentProgress method

When an NSAnimation object’s -startAnimation method is called, it automatically calls -setCurrentProgress: on itself until currentProgress is 1.0, meaning the animation has ended (currentProgress ranges from 0.0 to 1.0). The value is based on the duration and the animationCurve.
In this overridden method, we calculate the delta between the new and the initial doubleValue of the progressIndicator, multiply it by currentProgress and send it to the progressIndicator. That’s it.

How To Use NSProgressIndicator+ESSProgressIndicatorCategory

Add the category’s .h and .m files to your project, import it where you need it and update your progress indicator’s doubleValue by calling -animateToDoubleValue: with the doubleValue you desire to animate to.

The Source Code

The repository (a sample OS X app) is available on Github.

It was developed (and tested) on OS X Yosemite 10.10.3 using Xcode 6.3.1 but should work on earlier versions of the operating system.

More source code is available here (or directly on my github profile page) if you’re interested. If you have any questions or feedback regarding my open source projects, please be sure to mail or tweet me – I’m looking forward to your feedback!

Enjoy!