Enabling Your App for CarPlay 

Session 719 WWDC 2017

Understand how to enable your audio, messaging, VoIP calling or automaker app for CarPlay. Audio, messaging and VoIP calling apps use a consistent design that’s optimized for use in the car. Automaker apps provide vehicle specific controls and displays to keep drivers connected without leaving CarPlay. Explore best practices and learn about the tools and frameworks for CarPlay apps.

Hello and welcome to the Enabling Your App for CarPlay session.

My name is Albert and I’m an engineer on the CarPlay team.

Today we’ll be going through an overview of how apps behave in CarPlay, how to get your app integrated on the CarPlay platform and best practices and pitfalls to avoid.

Let’s look at how apps run in CarPlay.

When CarPlay is active some information will be available and accessible from the CarPlay screen.

If an app has posted now playing metadata and playback controls for audio content this information will also be accessible from the Now Playing app on the CarPlay Home screen.

Audio will be played through a car speaker system and some SiriKit intents will be supported in CarPlay.

If we user triggers of SiriKit intent that is not supported while in CarPlay Siri will notify the user that it is not available in the car.

Even though your app may not support CarPlay users may use your app while in CarPlay before they begin driving.

To ensure a great user experience for all apps in CarPlay make sure that your app doesn’t play audio unless requested since your app could override currently playing audio the user intended to play.

In some instances, your app will want to interact with other audio streams appropriately.

For spoken audio apps such as Audiobooks use this protocol so your audio will pause when other audio streams are active.

For navigation apps where guidance instructions are given intermittently use these two protocols, the latter of which will pause audio streams marked as spoken audio before initiating your audio session.

Because guidance voices will mix with other audio streams set your audio session to mixable so that it can interact with other audio streams.

For apps that have deeper CarPlay integration the app icon will appear on the CarPlay Home screen.

Apps that are launched in CarPlay will launch in the foreground on both the CarPlay and iPhone screen.

For apps that are not integrated with CarPlay only the iPhone screen will have the app in the foreground and CarPlay will only display the Home screen.

There are certain categories of apps that can support deeper CarPlay integration.

These are audio apps, messaging and VoIP apps and automaker apps.

Audio apps deliver music, news, podcasts and other audio content using a consistent design that’s optimized for use in the car.

Messaging and VoIP apps work using Siri and can be updated to appear in CarPlay.

Automaker apps provide vehicle specific controls and displays to keep drivers connected without leaving CarPlay.

If you think your audio, automaker, messaging or VoIP calling app has the potential to be supported by CarPlay tell us about it at the CarPlay developer portal.

There you’ll be able to request an entitlement to get your app running in CarPlay.

Keep in mind that certain assets and images will need to have CarPlay specific assets and to provide 2X and 3X sized images since the CarPlay screen has varying resolutions and sizes depending on a vehicle’s display.

For more guidance on icons and designing your app for CarPlay check out the iOS Human Interface Guidelines and the CarPlay Human Interface Guidelines.

While you can test the CarPlay app on iOS simulator in Xcode it is best to test on an actual device connected to a real vehicle head unit for realistic results.

For apps that will play audio the simulator has some limitations on playback state which does not reflect on what a user will actually experience.

To fully debug your app with LLDB support Xcode now supports wireless debugging so that an iPhone can be connected to a vehicle or aftermarket head unit while debugging your app.

For more information, please see the debugging with Xcode 9 session which will be available this week in WWDC.

If your app uses data protection for user data or content keep in mind that apps in CarPlay will likely run while the iPhone is pass code locked.

If your app has pass code protected data using the following types for files, keychains or SQL like databases shown here your data may be unavailable while in CarPlay and your app may behave unexpectedly.

Let’s take a closer look at getting your app integrated with CarPlay.

We will highlight the three categories of apps that support CarPlay integration, audio apps, messaging and VoIP apps, and automaker apps.

Let’s get started with audio apps.

Audio apps in CarPlay present content in an interface that’s optimized for the platform providing the user an easily navigable way to access their content.

Audio app developers provide a data source, as well as a navigation hierarchy for the CarPlay platform to render onscreen.

In addition, now playing information will be presented providing the user with relevant metadata, as well as adjustable commands for the user to handle playback speeds, tracks and other actions audio apps may support.

After receiving the app entitlement audio apps in CarPlay must at a minimum implement the MP playable content APIs, which include the data source and delegate in order for CarPlay to fetch content items and initialize playback.

Audio apps must also respond to MPRemoteCommandCenter events which let the user perform commands on your content, such as play, pause or skip tracks.

Finally, audio apps must set and update the MPNowPlayingInfoCenter dictionary which contain metadata on the item that is currently playing, such as item title, artist name or duration time.

Let’s take a closer look at how data is structured for audio apps.

CarPlay will ask for content items at a specific index path using an NSIndexPath.

And this is different than how NSIndexPath objects are used in UITableView.

Let’s go through an example shown here where the left most content items are the root items and can be represented in the user interface as individual tabs or a root table view.

Here’s the index paths for each content item represented in the hierarchy.

When CarPlay asks for a content item for a particular index path we, the audio app, would traverse the hierarchy for the requested content item.

In this example, we are asking for the first child of the first content which is the running playlist content item.

CarPlay will also ask for the number of child items of a particular index.

In this example, we are asking for the number of child items for the third child item of the second route content item.

In this example, we will return two.

Some vehicles may enforce limited content to show onscreen depending on whether the vehicle is in motion.

This can limit the number of rows shown onscreen, as well as container depth when drilling into content.

Your app can take these changes into account using MP Playable Content Manager.

To check if content limits are enforced implement the Delegate Callback Content Manager Did Update and check if the content limits are enforced.

From there your app can check the context properties to determine how many items are permitted in the table view and the maximum depth in the hierarchy your app is permitted to show.

If your app benefits from displaying data using tabs rather than exclusively table views you can add tabs by adding UI browsable content support section browsing in your app’s info.plist file.

We recommend having at most four tabs with short titles due to space constraints and for vehicles that have a narrow screen size, as well as accounting for the Now Playing button shown while content is playing.

Tab image assets will be rendered as template images on the CarPlay screen.

Now let’s talk about the Now Playing screen in CarPlay.

Some controls and metadata here are identical to what is shown in Control Center.

In general, what controls and data you see in Control Center should also be presented here in the CarPlay Now Playing screen.

This Now Playing screen can be accessed either by the user tapping Now Playing on the top right of your app’s navigation interface or through the Now Playing app on the CarPlay Home screen.

Your app’s name will appear on the top right of the Now Playing screen when it is active.

Setting metadata for CarPlay’s Now Playing screen is the same as Control Center and other sources.

Set a dictionary of information to MPNowPlayingInfoCenter and fill out as much of the entries as appropriate.

In addition, respond to playback commands so that the user can choose to adjust content such as play, pause, skip tracks or shuffle and repeat of playback queue.

These commands here are the ones that are supported on the CarPlay Now Playing screen.

New in iOS 11 is the ability to adjust and display the playback rate in the Now Playing screen.

To display playback rate in your app’s Now Playing screen in CarPlay add MPNowPlayingInfo PropertyDefaultPlaybackRate to MP Now Playing Info Center and respond to the change playback rate command with an array of supported rates in MPRemoteCommandCenter.

Here is an example of how you would implement playback rate adjustments and code.

In this sample, the default playback rate of the currently playing item is 1.0 and the supported playback rates here are 0.5, 1.0, 1.5, and 2.0.

When the user wants to adjust the playback speed increment the playback rate forward cycling back to the beginning if the audio is playing at the fastest supported rate.

In this code sample, playback rate will increment to 1.5 then 2.0 and then back to 0.5.

Some audio apps may respond to multiple commands in MP Remote Command Center.

Depending on what commands are enabled CarPlay’s Now Playing screen will combine certain relevant commands into a single button such as an ellipsis or a menu button replacing the previous track button.

For best practices, make sure that content is actually ready to be played or be displayed before calling the completion handlers in MP playable content data source and MP playable content delegate.

For apps that do not opt into tabs and only use table views the root table view must return at least one item.

CarPlay would show a loading activity indicator and will time out after period of time if an app has not responded with content.

If your app has some initial setup such as login credentials populate the first row with an item informing the user of the app’s current state onscreen.

That’s it for enabling audio apps and I’ll hand it off to Chris Whitney to discuss messaging and VoIP apps in CarPlay.

Hi, I’m Chris Whitney from the CarPlay engineering team.

Albert talked about audio apps now I will discuss a few more categories of apps that can integrate with CarPlay.

The first category I will cover is messaging and voice over Internet protocol calling apps.

In CarPlay Siri provides the interface for messaging and VoIP calling apps.

After the app icon is selected on the Home screen, Siri offers interactions for reading messages, starting a new message or starting an audio call.

Apps using SiriKit can already handle these actions, but the Siri request must contain the app’s name.

With a few additional changes messaging and VoIP apps can have a CarPlay experience that includes a Home screen icon, notifications, and a dedicated Siri interface.

Here are the requirements for an app to support messaging or VoIP calling in CarPlay.

Messaging apps must implement SirKit messaging intents and sign their app with an entitlement that is specific to CarPlay messaging.

Similarly, VoIP calling apps must implement the SiriKit calling intents and sign their app with an entitlement that is specific to CarPlay VoIP calling.

VoIP calling apps must also implement CallKit to inform CarPlay about the status of calls.

A single app can support both messaging and VoIP calling in CarPlay.

Let’s look into the SiriKit requirements in more detail.

For messaging apps, Siri sends messages using INSendMessageIntent.

Siri reads new incoming messages and searches for unread messages using INSearchforMessagesIntent.

And once done reading Siri marks messages as read by calling INSendMessageAttributeIntent.

All three intents are required to support a complete messaging workflow in CarPlay.

For VoIP calling apps, Siri starts audio calls using INStartAudiCallIntent and performs searches, such as for missed calls using INSearchCallHistoryIntent.

Both intents are required to support a complete calling workflow in CarPlay.

For details on SirKit see the session’s What’s New in SiriKit and Making Great SiriKit Experiences.

Any app that has already implemented CallKit gets a CarPlay interface for incoming and active calls.

But if your VoIP calling app hasn’t implemented CallKit yet that will be a requirement for CarPlay integration.

As a general overview, the app must report incoming calls to CallKit and handle the start, answer and end call actions.

Additional actions, such as mute, grouping, holding and keypad tones should be handled if supported by the app’s VoIP platform.

For more details on CallKit watch the enhancing VoIP apps with CallKit video from WWDC 2016.

Apps can show notifications in CarPlay for incoming messages and missed calls.

There’s some additional setup required to show notifications in CarPlay.

The CarPlay option must be included when requesting authorization for notifications and the messages must be separated into a notification category created with the Allow in CarPlay option.

This notifications category must be used exclusively for messages and it should not include notifications for other app features.

The notification category must specify a SiriKit intent to handle selection of the notification in CarPlay.

Only messaging or VoIP calling apps that meet the CarPlay requirements will be allowed to request authorization for showing notifications.

Also, users can use the Settings op to disable showing your app’s notifications in CarPlay.

Let’s look at the code for setting up notifications in CarPlay.

First, include the CarPlay option when requesting authorization for notifications.

Gracefully disable notifications related features if the user declines notification authorization.

Next, create a new message category that contains only notifications for messages.

Notifications for other app features, such as news or games should not be included in this notification category.

Assign an identifier to this category and make sure that any local or remote notifications for messages have the same category identifier.

Set up an intent identifier to configure the Siri interaction when the notification is selected in CarPlay.

Usually that will be INSearchForMessages IntentIdentifier which configures Siri to search for and then read the message that matches this notification.

There are a few best practices to follow when building messaging and VoIP calling apps.

Notifications should only include information like the sender and group name in the title and subtitle.

The contents of a message should not appear in CarPlay.

After reading a message, Siri will use INSentMessageAttributeIntent to mark content as read.

The read status should be reflected in the app and subsequent search for messages requests.

Since users may drive in and out of cellular coverage areas apps should use notifications to communicate any missed calls or message delivery failures.

This may require setting up additional notification categories as we have described earlier.

The final category of apps that can integrate into CarPlay are automaker apps.

Automaker apps are the only category of apps that can display a custom user interface in CarPlay.

In this example, the automaker app provides controls for adjusting the climate settings, selecting radio stations, and summoning roadside assistance.

Providing these controls in an automaker app allows the user to adjust the vehicle’s climate and radio without leaving CarPlay.

Automaker apps can take advantage of the iPhone’s Internet connectivity and powerful development platform to create additional vehicle features.

For example, this automaker app could enable Siri driven voice control of the climate and radio settings.

Automaker apps must be created by the car’s manufacturer to provide information and control features on a connected vehicle.

These apps must be signed with a specific CarPlay protocols entitlement.

They must display a user interface in CarPlay.

And they must only appear on supported vehicles.

CarPlay determines if an automaker app is supported on a given vehicle by matching the external accessory protocols declared by the vehicle with the CarPlay protocols entitlement sign in to the app.

Thus, it is important to consider potential automaker apps during vehicle development in order to have the appropriate set of protocols declared by the vehicle.

Here’s an example of how CarPlay matches automaker apps to vehicles.

This vehicle declares two protocols, a performance protocol for collecting vehicle statistics and a protocol for climate control.

As shown here, protocol names should be declared in reverse DNS format.

The automaker wants to take advantage of the vehicle’s performance statistics in a new app called Track Laps that’s designed for use on racetracks.

The app includes the performance protocol and its entitlements and since both the app and the vehicle support the performance protocol the Track Laps app will appear in CarPlay.

Automaker apps can also support multiple protocols.

This automaker decides to follow up on the success of Track Laps with a new app called Comfort Cruise that conveniently configures the radio and climate control with the driver’s favorite settings for commuting.

The app’s entitlements include both the climate protocol and a new radio protocol.

This vehicle doesn’t support the radio protocol, but since both the app and the vehicle support the climate protocol the Comfort Cruise app will appear in CarPlay.

After launching automaker apps should query the supported external accessory protocols and only display a user interface for the supported features.

In this example, the Comfort Cruise app should only show climate controls since the radio protocol is not supported on this vehicle.

The automaker wants to create another app called Charge Up that shows their electric vehicle charging stations.

To limit this app to only their electric vehicles the automaker declares a new electric protocol in the app’s entitlements.

Since this vehicle does not support the electric protocol the Charge Up app will not appear in CarPlay on this vehicle.

Building an automaker app requires communicating with the vehicle.

Automaker apps must communicate directly from the iPhone to the vehicle using the External Accessory framework.

Directly communicating using External Accessory improves the responsiveness of the app and avoids relying on connectivity to Internet services.

To use the External Accessory framework the app should define a custom protocol name as shown previously, implement the named protocol in the vehicle software, in the app observe accessory connection events, and upon connection initialize an EA session to create networking streams of the vehicle.

For more information see External Accessory programming topics.

Automaker apps can use UIKit to display a user interface on the CarPlay screen.

To create an interface in CarPlay the app should observe the UIScreen connection events and when the screen connects verify that the connected screen’s traits contain the CarPlay idiom.

Besides CarPlay, iOS also supports other external displays, such as an airplane display.

Only show CarPlay content on screens with the CarPlay idiom.

The app creates a UIWindow for the CarPlay screen and sets the root view controller to a custom UI view controller subclass.

Let’s see how this looks when all put together.

Here’s the code for displaying a view controller on the CarPlay screen.

Usually this code would be placed either in your UI application delegate or in a new class you’ve made for this code.

First, we’ll add a new class property to store the UIWindow that we will create for the CarPlay screen.

Next, we’ll define an instance method called updateCarWindow.

To check if a CarPlay screen is connected we look for a UIScreen that has the CarPlay idiom.

If no CarPlay idiom screens are available then release any previously created UIWindow since CarPlay may have disconnected.

If a CarPlay screen is connected initialize a new UIWindow for that screen and set up a custom rootViewController that contains the content that should appear in CarPlay.

Here we are using a UI view controller subclass called carViewController.

That class will need to be implemented.

Your app may launch after CarPlay connected.

To handle that scenario call updateCarWindow early in your application’s lifecycle, such as an application did finish launching with options.

Since CarPlay can also connect after your app is launched listen for the UIScreenDidConnect and UIScreenDidDisconnect notifications and call UpdateCarWindow in response to those events.

There are a few differences in UIKit behavior on the CarPlay screen compared to the iPhone’s main screen.

UIButtonTypeSystem displays with the default CarPlay style and is the recommended way to create buttons since it provides a style and behavior consistent with other CarPlay apps.

In CarPlay, UITableViewController may limit the length of tables and for vehicles with a hardware navigation device, such as the [inaudible], the corresponding focus movements are handled through UIFocusEnvironment and the related focus classes.

Note that not all system user interface elements provided by UIKit are available to automaker apps.

There’s a selection of SiriKit intents relevant to automaker apps.

The commands intents are available to all apps.

They don’t require a CarPlay connection nor participating in the CarPlay app program.

But an automaker app is a great place to implement these intents, which include locking the vehicle, checking the fuel level and sounding the horn.

There’s also a set of intents that require a CarPlay connection and can only be implemented by automaker apps.

The CarPlay intents include climate control, defroster and seat heater settings.

Also included are intents for tuning the radio and selecting an audio source.

There are a few best practices for automaker apps.

The first is to make your app useful even when CarPlay is not available.

For example, when disconnected from CarPlay an automaker app can use Internet services to remotely communicate with the vehicle.

Consider backwards and forwards compatibility in your automaker app.

App updates should continue to support older vehicles and new features should not break existing versions of the app.

Simplify the user interface, most CarPlay apps should only contain fundamental interface elements, such as buttons, labels, tables, navigation bars and tabs.

Finally, if your automaker app supports vehicles with a hardware navigation device such as a [inaudible] determine how focus should move between the UI elements.

We hope that you’ve learned how to integrate an audio, messaging, VoIP calling or automaker app into CarPlay.

For more information about CarPlay, see developer.apple.com.

You can also learn more in related sessions.

See the Debugging with Xcode 9 session for more information about debugging apps during a wired CarPlay connection.

For more information about SiriKit, see the sessions What’s New in SiriKit and Making Great SiriKit Experiences.

To learn how wireless CarPlay works watch the Developing Wireless CarPlay Systems video.

Videos from WWDC 2016 are available for both CallKit and CarPlay systems development topics.

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