Plugin for Plugin, или расширяем Android New Build System

2. Plugin for plugin,
or extending
Android New Build System
Anton Rutkevich

3. About me
› 4+ years of Android development
› Mobile game-dev experience
› At Yandex:
1. Mobile Yandex.Metrica
2. Continuous Integration

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Intro
Why do I need this?

5. What can be done?
› Additional resources/code/manifest processing
› Output processing (apk, aar, jar)
› Other things

6. Flavors
2 Flavors!
Story
Prod / test serversLogs on/offTest / prod analyticsAds on/off
Unique build number!...
I want to configure it
myself!
3 Flavors?Hmm…

7. Story
Prod / test
servers
Flavors!
Logs on/offTest / prod
analyticsAds on/offUnique build
number!...
I want to
configure it
myself!
2 Flavors!3
Flavors?Hmm...
Android devManager

8. How should it work
Java code build.gradle Teamcity
Actual value:
"https://my.server.com"
CI server can do it
Our job

9. Insert CI value into BuildConfig.java
// app/build.gradle
apply plugin: 'com.android.application'
android {
defaultConfig {
buildConfigField "String", "URL", ""${teamcity['server-url']}""
buildConfigField "String", "URL", ""#server-url""
}
}
project.teamcity = [
"server-url" : "https://my.server.com"
// ...
]
buildConfigField "String", "URL", ""${teamcity['server-url']}"".

10. Use BuildConfig.java from Java
public class SomeJavaClass {
// ...
public static final String SERVER_URL = "https://my.server.com";
public static final String SERVER_URL = BuildConfig.URL;
// ...
}
public static final String SERVER_URL = "https://my.server.com";

11. BuildConfig placeholder plugin
› Replaces placeholder values with values from some map
› Map can come from anywhere

12. Goal
// app/build.gradle
apply plugin: 'com.android.application'
apply plugin: 'placeholder'
placeholder {
replacements = project.teamcity
}
android {
defaultConfig {
buildConfigField "String", "URL", ""#server-url""
}
}

13. Table of contents
› Gradle basics
› New Build System workflow
› Hello, Gradle plugin!
› Extending Android New Build System

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Gradle basics
Tools we will use

15. Plugins everywhere
NBS

16. Tasks
› Can be configured with { }
› Consist of actions
› Can depend on other tasks
› Can have inputs / outputs

17. Task consists of actions
Action Action
Action Action
doFirst() doLast(), or <<
Task

18. Tasks execution order
Task 2
Task 3
Task 4
Execution order
dependsOn
Task 1
Task 2 Task 3 Task 4 Task 1
dependsOn
dependsOn

19. Outputs
Task inputs / outputs
TaskInputs
Inputs & outputs did not change
=>
UP-TO-DATE

20. Task example
task myTask {
ext.myMessage = "hello"
}
myTask << {
println myMessage
}
task otherTask(dependsOn: myTask)

21. Task example output
>> gradle otherTask
:app:myTask
hello
:app:otherTask

22. Build lifecycle
Initialization Configuration Execution
settings.gradle
Projects creation
Projects
configuration
Tasks creation
Tasks configuration
project.afterEvaluate { }
Task graph execution
Task graph
build.gradle
Build initialization

23. The image cannot be displayed. Your computer may not have
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The New Build System
workflow
What's so special?

24. What tasks will be launched?
build
check assemble
assembleDebug assembleRelease
assemble<VariantName>Guaranteed

25. Android project build overview

26. Tasks we will need
assemble<VariantName>
generate<VariantName>BuildConfig
compile<VariantName>Java
....
....
....

27. Variant API
Source code
is your documentation!
› Access to most variant's tasks
› Variant output related properties
› Different for apps & libraries

28. The image cannot be displayed. Your computer may not have
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Hello, Gradle plugin!
The first steps

29. The very basic one
src/main/groovy/com/example/gradle/PlaceholderPlugin.gradle
public class PlaceholderPlugin implements Plugin<Project> {
@Override
void apply(Project project) {
project.task('hello') << {
println "Hello Gradle plugin!"
}
}
}

30. Bind plugin class to plugin name
src/main/resources/META-INF/gradle-plugins/placeholder.properties
implementation-class=com.example.gradle.PlaceholderPlugin

31. Extension
Extension

32. Add extension
src/main/groovy/com/example/gradle/PlaceholderExtension.gradle
class PlaceholderExtension {
def replacements = [:]
}

33. Add extension
@Override
void apply(Project project) {
project.task('hello') << {
println "Hello Gradle plugin!"
println "Hi, ${project.placeholder.replacements}"
}
}
PlaceholderExtension extension = project.extensions.create(
"placeholder", PlaceholderExtension
);
println "Hello Gradle plugin!"

34. Use extension
// app/build.gradle
apply plugin: 'placeholder'
placeholder {
replacements = ["server-url" : "https://my.server.com"]
}
---------------------------------------------
>> gradle hello
:app:hello
Hi, [server-url:https://my.server.com]

35. The image cannot be displayed. Your computer may not have
enough memory to open the image, or the image may have
been corrupted. Restart your computer, and then open the file
again. If the red x still appears, you may have to delete the
image and then insert it again.
Extending
The New Build System
Let's do it!

36. Check for New Build System
// PlaceholderPlugin.groovy
@Override
void apply(Project project) {
if (project.hasProperty("android")) {
PlaceholderExtension extension = project.extensions.create(
"placeholder", PlaceholderExtension
);
def android = project.android
// all code goes here
}
}

37. Let the New Build System do its job
// PlaceholderPlugin.apply()
if (project.hasProperty("android")) {
PlaceholderExtension extension = project.extensions.create(
"placeholder", PlaceholderExtension
);
def android = project.android
project.afterEvaluate {
// at this point we have all
// tasks from New Build System
}
}

38. Process every variant
// PlaceholderPlugin.apply()
project.afterEvaluate {
if (android.hasProperty('applicationVariants')) {
android.applicationVariants.all { variant ->
addActions(project, variant, extension)
}
} else if (android.hasProperty('libraryVariants')) {
android.libraryVariants.all { variant ->
addActions(project, variant, extension)
}
}
}

39. Add task
// PlaceholderPlugin.groovy
def addActions(Project project, variant,
PlaceholderExtension extension) {
Task processPlaceholders = project.task(
"process${variant.name.capitalize()}Placeholders"
)
processPlaceholders << {
println "I will replace ${variant.name}!"
}
}

40. Insert task into build process
assemble<VariantName>
generate<VariantName>BuildConfig
compile<VariantName>Java
....
....
....
process<VariantName>Placeholders

41. Insert task into build process
// PlaceholderPlugin.groovy
def addActions(Project project, variant,
PlaceholderExtension extension) {
Task processPlaceholders = ...
...
variant.javaCompile.dependsOn processPlaceholders
processPlaceholders.dependsOn variant.generateBuildConfig
}

42. Does it really work?
>> gradle assembleDebug
:app:preBuild
...
:app:generateDebugBuildConfig
...
:app:processDebugPlaceholders
I will replace debug!
:app:compileDebugJava
...

43. Actual work. Perform replacements
// PlaceholderPlugin.addActions()
processPlaceholders << {
def buildConfigFile = getBuildConfig(variant)
extension.replacements.each { replacement ->
project.ant.replace(
file: buildConfigFile,
token: "#${replacement.key}",
value: replacement.value
)
}
}

44. Handling inputs / outputs
process
Placeholders
BuildConfig.java
BuildConfig.java
replacements
generate
BuildConfig
...
replacements
<< Action
BuildConfig.java

45. Replace task with 'doLast'
// PlaceholderPlugin.addActions()
processPlaceholders << {
variant.generateBuildConfig << {
def buildConfigFile = ...
extension.replacements.each { ... }
}
variant.generateBuildConfig.inputs.property(
"replacements", extension.replacements
)
processPlaceholders << {

46. │ We've done it!

47. Remember how to use it?
// app/build.gradle
apply plugin: 'com.android.application'
apply plugin: 'placeholder'
placeholder {
replacements = project.teamcity
}
android {
defaultConfig {
buildConfigField "String", "URL", ""#server-url""
}
}

48. Does it work?
app/build/generated/source/buildConfig/debug/com/example/
sample/BuildConfig.java
public final class BuildConfig {
// Fields from default config.
public static final String URL = "https://my.server.com";
}

49. The image cannot be displayed. Your computer may not have
enough memory to open the image, or the image may have
been corrupted. Restart your computer, and then open the file
again. If the red x still appears, you may have to delete the
image and then insert it again.
To summarize

50. Key steps
› Create Gradle plugin
› Inside afterEvaluate { }
› Process every variant
› Add action to generateBuildConfig
› Handle inputs / outputs

51. What's next?
› Default values support
› Errors handling
› Publish ( jcenter / mavenCentral / other )

52. Links
Gradle
http://www.gradle.org/
The New Build System
http://tools.android.com/tech-docs/new-build-system
http://tools.android.com/tech-docs/new-build-system/build-workflow
Github sample
https://github.com/roottony/android-placeholder-plugin

53. Thank you for your attention!
anton.rutkevich@gmail.com
Anton Rutkevich
Senior software engineer
antonrut@yandex-team.ru