Slices: What They're Not Telling You

Slices are UI templates that can display rich, dynamic, and interactive content from your app from within the Google Search app and later in other places like the Google Assistant.

Slices will start appearing soon for users, but you can start building today.

You can customize your Slice with color, text, imagery, video, and more to match your app's design.

(That's) What I'm Talkin' 'bout

• What are slices, really?
• How do we create and publish them?
• How do we host and render them?
• Why would we bother?

A Problem As Old As Time

The Android Solution You're Used To

The Slice Scenario

A Slice of... Stuff

• What Provider Provides
  • Structured data (e.g., weather forecast)
  • Metadata for suggested visual organization
• What Host Does With It
  • Whatever it wants
  • Probably uses library-supplied rendering classes

Pieces of a Slice

• androidx.slice:slice-builders-ktx dependency
  • Kotlin slice-building DSL
  • Everything involving slices requires androidx!
• SliceProvider Subclass
  • Plus corresponding manifest entry
  • Key method: onBindSlice()

Trying Your Slice

• Install the Slice Viewer app
• Run Your Slice in the Viewer from Studio
  • Set up a slice-content run configuration
  • Tie it to your provider's authority

Slices... Live!

• Your slices are identified by a Uri
• When a slice changes, use notifyChange()
• Slice hosts will automagically find out about the change and fetch a fresh slice
• Scenarios
  • New slice with asynchronous data load
  • Underlying data changes for existing slices
  • In response to user input from the slice

Slices... LiveData!

Rendering a Slice

• Add a SliceView to your UI
• Configure the SliceView (e.g., mode)
• Get a SliceLiveData using fromUri()
• Use observe() to tie the SliceView to the SliceLiveData
• That's it!

Custom Slicing

• Get a SliceLiveData using fromUri()
• observe() with your own Observer
• Consume the Slice Objects
  • Tree of SliceItem objects
  • SliceMetadata to help decode a Slice
  • Poorly documented
• Use case: SliceProvider testing

Problem: Discovery

• The host needs the Uri to the provider
• Possible Solutions
  • <intent-filter>
  • <meta-data>
  • Any already-established IPC mechanisms
• Key: agreed-upon rules between M hosts and N providers

What Are They Good For?

E-Commerce

• E-commerce app publishes slices
• Uri contains referral ID and search keyword
• Hosts render the slice, make $$$
• Benefits
  • No ad SDK requirement: just a Uri
  • Richer than image ad banners
  • Less costly than WebView

What Are They Good For?

App Widgets 2.0

• Launcher developers agree to specification for Uri discovery
• App publish slices
• Launchers add to "widgets" catalog
• Slice to RemoteViews bridge to support incompatible home screens, with same content

What Are They Good For?

Knowledge App Integration

• Wikipedia, etc. publish slices with search terms in Uri structure
• Apps can embed those slices in popups for term definitions, etc.
• Once again: no heavyweight SDK, no WebView

What Are They Good For?

OMG I'm Running Out Of Time

• App suite integration
• ACTION_SEND alternative
• Specialized slice hosts (screenreaders, "portals", etc.)
• "Turnkey" slice providers (RSS/Atom, Swagger, etc.)
• Developer tools (Sonar plugin, testing library)

Compatibility Concerns

• Slice spec and implementation need to be versioned
• Slice Host Must Be Flexible
  • Graceful degradation for older-spec slices
  • Defensive programming for newer-spec slices
  • Not implemented in 1.0.0-alpha3 slice rendering code, apparently
• Possible differences between library, platform implementations

Questions?