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NSTouchBarItem

A UI control shown in the Touch Bar on supported models of MacBook Pro.

Declaration

@MainActor class NSTouchBarItem

Overview

An instance of the NSTouchBarItem class is called an item. It appears to the user on the Touch Bar, typically along with other items, within the (invisible) bounds of the view for an NSTouchBar object, called a bar.

You use an item by adding it or its identifier to one or another of a bar’s arrays, depending on your app’s architecture and on the user customization you want to support. Because of the close interaction between bars and items, be sure you have read the overview for the NSTouchBar class before continuing here to learn about items.

AppKit provides a rich set of subclasses of NSTouchBarItem, each of which is described in the corresponding class reference document:

  • An NSCandidateListTouchBarItem object (a candidate-list item), along with its delegate, provides a list of textual suggestions for the current text view

  • An NSColorPickerTouchBarItem object (a color picker item) provides a system-defined color picker

  • An NSCustomTouchBarItem object (a custom item) contains a responder of your choice, such as a view, a button, or a scrubber (an instance of the NSScrubber class)

  • An NSGroupTouchBarItem object (a group item) provides a bar to contain other items

  • An NSPopoverTouchBarItem object (a popover item) provides a two-state control that, when touched or pressed, expands into its second state, showing the contents of a bar it owns

  • An NSSharingServicePickerTouchBarItem object (a sharing service picker item), along with its delegate, provides a list of objects eligible for sharing

  • An NSSliderTouchBarItem object (a slider item) provides a slider control for choosing a value in a range

The two most commonly-used item classes are NSCustomTouchBarItem and NSPopoverTouchBarItem.

Refer to the following sample code projects which demonstrate how to use NSTouchBarItem and related classes:

Custom items

You typically use a custom item (an instance of the NSCustomTouchBarItem class) to hold a view. For example, to place a button in the Touch Bar, proceed as follows:

  1. Use an NSButton convenience initializer such as init(title:image:target:action:) to create and configure the button.

  2. Set the view property for a custom item to point to the new button.

Popover items

A popover item (an instance of the NSPopoverTouchBarItem class) — the second commonly-used type — lets you provide a new bar (an NSTouchBar object) when a user taps, or presses-and-holds, on the collapsed representation of the popover item.

In its expanded state, a popover appears as an overlay above other items in the Touch Bar.

To show a bar when a user taps a popover item, specify a bar in the item’s popoverTouchBar property. Enable press-and-hold by specifying a bar in the pressAndHoldTouchBar property. The press-and-hold feature is suitable only for a simple popover, such as one that contains a single segmented control (an instance of the NSSegmentedControl class) or slider (an instance of the NSSliderTouchBarItem class).

The system automatically shows a chevron in the popover item under the following conditions: You specify the same NSTouchBar object for both pressAndHoldTouchBar and popoverTouchBar properties, and you use the default view for the popover item’s collapsedRepresentation property.

If you provide a popover item that contains a scrubber (an NSScrubber instance), you’ll likely want to dismiss both the scrubber and the popover after the user makes their selection in the scrubber. A good approach to achieve this user interaction is to subclass NSPopoverTouchBarItem, employing your instance of the subclass as the scrubber’s delegate. You can then configure the delegate object, within its didFinishInteracting(with:) method, to call the popover’s dismissPopover(_:) method.

If you place a segmented control in a bar for a popover item, take care not to use NSSegmentedControl.SwitchTracking.momentary option of the NSSegmentedControl.SwitchTracking enumeration because doing so interferes with the user’s operation of the control.

Other common item types

To provide a slider item, always use the NSSliderTouchBarItem class, which employs a standard slider but is optimized for user interaction with the Touch Bar. (That is, don’t instead add an NSSlider object directly to a custom item.)

A group item (an instance of the NSGroupTouchBarItem class) is a container that provides a bar, in its groupTouchBar property, with its own array of items. You can enable customization for the items in a group’s contained bar, in the same way you would for items directly within a top-level bar. Using a group item lets you provide different user customization rules for different parts of the Touch Bar. Using a group item also lets you enable centering of the group within the Touch Bar.

A spacing item lets you add custom spacing between items in a bar. Specify a spacing item for a bar by assigning the fixedSpaceSmall, fixedSpaceLarge, or flexibleSpace identifier to an item, and adding that item to the bar’s items array. The system automatically instantiates and configures spacing items based on the identifiers you specify.

Configuration

You must configure each item with a unique identifier, and can optionally assign a visibility priority or tag it as a principal item.

NSTouchBarItem identification. You must provide a unique identifier for each item in the bar, apart from spacing items. Specify an identifier, of type NSTouchBarItem.Identifier (called an item identifier), for each item when you initialize it. The item identifier serves as a persistable weak reference to the item. The system uses item identifiers to populate bars and to track and record changes for user customization.

NSTouchBarItem priority for visibility. If the system is showing a bar in the Touch Bar, but horizontal space is constrained and the bar defines more items than will fit, the system hides some of the items. You influence this hide/show behavior by setting a value for the visibilityPriority property of each item.

Lower-visibility-priority items get hidden by the system, as needed, before higher-visibility-priority items do.

To set visibility priority, use the constants in the NSTouchBarItem.Priority enumeration, or assign an integer value. The value 0 indicates normal visibility priority. Visibility priority increases with increasing numerical value. The low constant provides a value of -1000; the high constant, a value +1000. You can use integers outside of this range if you need to.

The system hides or shows groups of identical-priority items (defined within a single bar) together. The one exception to this rule is for items whose visibility priority is normal; these items get hidden one-by-one, with the normal-priority item farthest to the right getting hidden first. If horizontal space later increases in the Touch Bar, and hidden, normal-priority items become eligible for display, the system first shows the most recently-hidden of those items.

Principal Items. Within a bar, you can optionally specify an item as having special significance by employing the principalItemIdentifier property. The system attempts to center a principal item within the Touch Bar. If you want a group of items to appear centered in the Touch Bar, designate the group item (of type NSTouchBarItem) as the principal item.

If more than one bar in the responder chain is eligible to be visible in the Touch Bar, and more than one of those has a principal item, the system determines which one to center in the Touch Bar.

Fonts, images, and colors

When using a button in a custom item, don’t attempt to set the button title’s font. In the Touch Bar, the system specifies fonts for standard controls.

If you need to specify a font, such as for custom drawing, use the systemFont(ofSize:) class method (or related methods) of the NSFont class. Use a font size of 0 to automatically obtain appropriate sizing for the Touch Bar.

If you use an image in a button or other control in the Touch Bar, take care to employ a template image. Template images in the Touch Bar respond automatically to system white-point changes, and automatically react to user interactions. The overview in this document lists the built-in Touch Bar template images.

To use your own image assets, use Retina-resolution images, designated as @2x in your asset catalog and with a maximum height of 30 points (corresponding to 60 pixels).

To set colors on objects within an NSTouchBarItem object, use AppKit named colors and use a bezel color property (available starting in macOS 10.12.1). Named colors appear correctly in the Touch Bar, support appearance vibrancy, and respond to system white-point changes. In a button or a segmented control, employ the bezel color property to ensure appropriate appearance in the Touch Bar.

To set the background color on a button within a custom item, use code like this:

myButton.bezelColor = NSColor.controlColor

To set color on text and glyphs in the Touch Bar, use the following colors from the NSColor class:

The system automatically changes the relative brightness and the white-point of these colors, depending on the ambient light, and depending on other factors such as keyboard backlight level. Always use these colors, or colors that dynamically derive from these colors, for control backgrounds, text, icons, and glyphs in the Touch Bar.

Handling touch events

The easiest way to handle touch events in an item is to use AppKit controls, such as by adding a button, a segmented control, or a scrubber to the item. Standard AppKit controls convey touch events to your specified targets automatically, so use standard controls whenever possible in your app.

If standard controls are insufficient, you can create composite views with a combination of standard controls, custom views, and gesture recognizers that you manually add to those custom views.

If you require the lowest-level of control for touch event processing, you can use the NSTouch class directly. You might go this route, for example, to provide good user feedback in the case of a control placed within a scroll view.Direct use of touch methods allows fine-grained control over interaction. You can, for example, highlight a control immediately upon a user touching it, and then remove the highlight if the user then, without lifting the finger, performs a scroll gesture.

If using the NSTouch class directly, be sure to implement the touchesCancelled(with:) responder method, because users can perform touch interactions that result in canceled touches.

Topics

Creating a bar item

Identifying a bar item

Managing item visibility

Configuring bar customization

Subclassing bar items

Using template images

See Also

Touch Bar items