A Room with a ViewModel

Investigating the Android Architecture Components

Architecture Components

• Released in May as part of Google I|O 2017
• Google's take on "the issues of the day"
• Room: ORM-ish database access
• Lifecycle: the Loader framework for a new era

Room: Entities

TL;DR: POJOs with Annotations

• @Entity with metadata about names, indices, foreign keys, etc.
• @PrimaryKey on the field that is unique
• @Embedded to pull out some columns into separate nested object
• @Ignore for things that Room should... y'know...

Room: DAO

Has Nothing To Do with Confucian Philosophy

• @Dao to identify its role
• @Query methods with SQL statements containing placeholders, returning entities or other POJOs
• @Insert, @Update, @Delete methods for rest of entity CRUD
• Use @Query for non-entity CRUD (delete by ID, delete all, etc.)

Room: RoomDatabase

A Database! For, Um, Room!

• @Database annotation listing entity classes, version code
• abstract methods returning DAO instances
• Create instance using Room.databaseBuilder()

Room: Types

Wait? Everything Isn't a String?

• Implement pair of methods, annotated with @TypeConverter, to round-trip convert from whatever you want into a simple type
• Add @TypeConverters annotation to appropriate scope
  • Database
  • Entity
  • Field
  • Etc.

Room: Relations

OK, Now Things Get Weird

• @ForeignKey on child, pointing to columns in parent and providing update/delete rules
• And... that's it
  • No methods on parent to retrieve child
  • No methods on child to retrieve parent
  • Nothing in DAO to load object graph... except @Relation, which has issues
  • Argument: direct relations leads to accidental I/O on main application thread

Room: Migrations

Unless You Get the Schema Right on the First Try

• Create instances of Migration
• Implement migrate(), akin to onUpgrade() of SQLiteOpenHelper
• Work with SQLite "directly", not via Room
• Register migrations with RoomDatabase when building
• Dedicated test support library

Room: Encryption

What? You Actually Expected Me Not To Talk About Security?

• SupportSQLite... classes as abstraction around SQLite implementation
• CWAC-SafeRoom: bridge between Room and SQLCipher for Android
• Add dependency, create SafeHelperFactory with passphrase, add to RoomDatabase.Builder, and you're done

Lifecycles

The Story of Our Android Developer Lives

• LifecycleOwner: Something that has a Lifecycle
  • LifecycleActivity
  • LifecycleFragment
  • ProcessLifecycleOwner: meta-lifecyle, aggregated for all activities
  • LifecycleService
  • Anything else you choose to teach about a Lifecycle

LiveData

Because UndeadData Was Too Creepy

• Implements cut-down RxJava-style reactive system with observers
• Lifecycle-aware, so will clean up after itself
• Wrap @Query response in LiveData for reactive Room
  • ...though you can use RxJava Flowable, etc. too
  • Automatic reactive notification when data changes through Room
• Can create your own LiveData for other data sources

ViewModel

Putting the VM in MVVM

• Configuration-change-aware container of data
• Designed to hold LiveData and other state for rendering your UI
• In reality, thin (and strange) wrapper around retained fragments
• Only works with FragmentActivity and backport Fragment

Where Things Go From Here

• Expect slow progression through alpha and beta releases until 2017 Q4/2018 Q1
• Expect more sample code from Google to use this stuff
• Expect another pulse of activity in time for Google I|O 2018

Questions?