Gradle and Your Android Wearable Projects

Gradle and
Your Android
Wearable
Projects
Copyright © 2014 CommonsWare, LLC

One APK To Rule Them All
●

One APK, regardless of device type

●

Original Android development vision

●

●

Still works for conventional apps... within
reason
Starts to break down as you go beyond
traditional device types into things like
wearables


Presentation Terminology
●

Device
●

Runs a mainstream mobile operating system, designed for
multiple form factors
–
–

●

Today: Android, Tizen
Tomorrow: who knows?

Accessory
●

●

●

Runs some dedicated OS
Most/all app logic resides on tethered phone or tablet

Hybrid: dedicated OS, but apps run on wearable


Terminology Examples
●

Device
●
●

Omate TrueSmart

●

I'm Watch

●

●

Google Glass

Samsung Gear 2 / Gear 2 Neo

Accessory
●
●

Samsung Gear Fit

●

●

SONY SmartWatch/SW2
Fitbit

Hybrid
●

Pebble


Wearables: Why Multiple APKs?
●

CPU architecture

●

Distribution channel (e.g., no Play Services)

●

Per-device libraries
●

Licensing

●

Bulk

●

API level

●

Entry points and security

●

Resources


A Specific Wearable Scenario
●

Main App
●

●

SONY SW2
●

●

Phones, tablets, modern Android wearable devices
(Omate TrueSmart)
Dedicated libraries

I'm Watch
●

Workarounds where new API options are missing


Other Possible Scenarios
●

Samsung Gear Fit
●

●

Dedicated libraries, dedicated distribution channel

Google Glass
●

●

●

New UI backed by common code
Dedicated distribution channel

Pebble
●

Separate C language project for on-device portion of app

●

Android project for the on-phone tethered side


Classic Solution: Library Project
●

Common materials in the library
●

Java code

●

Standard resources

●

Per-device apps that leverage the library

●

Works, but a bit clunky
●

Future: relegated to cases where library needs to
be used by totally disparate apps


Gradle Solution: Product Flavors
●

One Project, N Flavors
●

●

Alternative Java classes (one per flavor)

●

●

Additions to manifest
Additional or replacement resources

Each Flavor Generates Own APK
●

●

Unique package name, but independent from your
R classes

Other techniques available as well


What Is Gradle?
●

Role: Build Automation
●

●

Implementation: It's Groovy
●

●

Think Ant plus Maven plus other goodness
DSL implemented in Groovy, blending declarative
structures and full-blown scripting

Provider: Gradleware
●

Open source, Apache licensed


Gotta Getta Gradle
●

Direct Download

●

The Gradle Wrapper
●

gradlew script and related files in a repo

●

Designed for boostrapping
–
–

●

Running the script does a Gradle build
Running the script installs Gradle itself if development
machine does not have it

Actual Gradle comes from wherever script says
–

Net: only use this if you REALLY trust the source


The Basic Gradle Process
●

Write build.gradle File
●

●

Same role as build.xml for Ant, etc.

●

●

Describes sources and results
Usually in root of project directory

Run gradle / gradlew
●

Supply task name as command-line parameter

●

Optional: IDE integration


Escape From Eclipse
●

Exporting a build.gradle
●

Export wizard in Eclipse through current ADT

●

Choose project(s) to export

●

Get build.gradle files generated for you
–

●

A bit more complicated than the normal build.gradle
starting point due to legacy project structure

NOTE: Not Kept in Sync!
●

Project changes in Eclipse do not mirror to
build.gradle!


build.gradle: High-Level View
●

buildscript {}
●

Describing dependencies for running the build

●

Key: Android plugin

●

apply plugin: 'android'

●

dependencies {}
●

●

Describing compile-time dependencies (JARs, etc.)

android {}
●

Tailoring what Android builds for you


Tons o' Tasks
●

assemble*
●

●

●

Compiles APK for you
Tied to “build type” (assembleDebug,
assembleRelease are default)

install*
●

Installs APK on device for you, after assembly

●

Only installDebug works by default
–

installRelease requires configuring your signing
keys


Project Structures, Old and New
●

Original Recipe
●

●

●

src/, res/, assets/ in top-level project directory
libs/ also in top-level project directory

New Project Structure
●

src/, res/, assets/ in subdirectory
–
–

●

main/ by default
Others by “build type” or “product flavor”

libs/ remains in top-level directory
–

Or gone, replaced by artifacts


Pieces of New Project Structure
●

Source Sets

●

Build Types

●

Product Flavors

●

Build Variants


Source Sets
●

Gradle Construct for Organizing “Source”
●

●

In Android's case, includes resources and assets

Vision
●

●

Have one main/ source set with most of your code
Have alternatives in other source sets, used
conditionally
–

Resources, assets: can replace main/ source set

–

Java: cannot replace main/, can only add


Build Types
●

Android Plugin Construct for Describing
Output Variations
●

●

Two build types come default: debug and
release

Build Types Configurable
●

●

●

Project properties in build.gradle
Source sets

Define Others As Needed
●

Smoke tests, debuggable-release builds, etc.


Product Flavors and Build Variants
●

Product Flavors
●

●

●

Android plugin construct for different deployment
variations
None defined by default, can create your own

Build Variants
●

●

Cross product of build types and product flavors
Drive task names (assembleSonyDebug) and
results


Quick Dependencies Overview
●

Sub-Projects

●

JARs
●

●

AARs
●

●

compile fileTree(), sub-projects, or replace
with artifacts
Compiled Android library projects

Artifacts
●

Maven Central and/or your own repositories

●

JARs and AARs supported


Specific Scenario Build Script
●

One Project

●

Three Product Flavors
●

standard

●

sony

●

imwatch


Flavor-Specific Changes
●

SONY
●

sonyCompile

●

Hand-rolled local artifacts for SONY libraries
–

●

Long-term: hope they publish to Maven Central or own
artifact repository

I'm Watch
●

Resources


What You Get
●

Three APKs
●

●

●

Two for Play Store distribution (standard and
SONY)
One for dedicated distribution (I'm Watch)

In general, one APK per build variant
●

For release = one APK per product flavor


Gradle Pros...
●

One build system to rule them all
●

●

...in the fullness of time

Much more powerful than Ant for
command-line builds

●

More flexible options for code reuse

●

Richer build script syntax


...and Cons
●

Android Studio still a work in progress

●

No Eclipse support yet

●

Gradle for Android still has its own bugs and
limitations

●

Breaking changes with updates

●

AAR packaging far from universal
●

...let alone being artifacts for easy consumption


Where To Learn More
●

http://tools.android.com/
●

Home of the Android tools team

●

Information on Gradle for Android, Android Studio
–

●

http://gradle.org
●

●

For general Gradle information

http://gradleware.com
●

●

Note: much is out of date!

Firm behind Gradle's development, offering training and consulting

http://commonsware.com/Android
●

Some book by some balding guy

●

Several chapters on Gradle for Android


Gradle and Your Android Wearable Projects

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