Goals of the new Build System
The goals of the new build system are:
- Make it easy to reuse code and resources
- Make it easy to create
several variants of an application, either for multi-apk distribution or
for different flavors of an application
- Make it easy to configure, extend and customize the build process
- Good IDE integration
Gradle is an advanced build system as well as an advanced build
toolkit allowing to create custom build logic through plugins. Here are
some of its features that made us choose Gradle:
- Domain Specific Language (DSL) based on Groovy, used to describe and manipulate the build logic
- Build files are Groovy
based and allow mixing of declarative elements through the DSL and using
code to manipulate the DSL elements to provide custom logic.
- Built-in dependency management through Maven and/or Ivy.
- Very flexible. Allows using best practices but doesn’t force its own way of doing things.
- Plugins can expose their own DSL and their own API for build files to use.
- Good Tooling API allowing IDE integration
Requirements
- Gradle 2.2
- SDK with Build Tools 19.0.0. Some features may require a more recent version.
Basic Project Setup
A Gradle project describes its build in a file called
build.gradle located in the root folder of the project. (See
Gradle User Guide for an overview of the build system itself.)
Simple build files
The most simple Android project has the following build.gradle:
buildscript {
repositories {
jcenter()
}
dependencies {
classpath 'com.android.tools.build:gradle:1.3.1'
}
}
apply plugin: 'com.android.application'
android {
compileSdkVersion 23
buildToolsVersion "23.1.0"
}
There are 3 main areas to this Android build file:
buildscript { ... }
configures the code driving the build. In this case, this declares that
it uses the jCenter repository, and that there is a classpath
dependency on a Maven artifact. This artifact is the library that
contains the Android plugin for Gradle in version 1.3.1. Note:
This only affects the code running the build, not the project. The
project itself needs to declare its own repositories and dependencies.
This will be covered later.
Then, the com.android.application plugin is applied. This is the plugin used for building Android applications.
Finally, android { ... }
configures all the parameters for the android build. This is the entry
point for the Android DSL. By default, only the compilation target, and
the version of the build-tools are needed. This is done with the compileSdkVersion and buildtoolsVersion properties.
The compilation target is the same as the target
property in the project.properties file of the old build system. This
new property can either be assigned a int (the api level) or a string
with the same value as the previous target property.
Important: You should only apply the com.android.application plugin. Applying the java plugin as well will result in a build error.
Note: You will also need a local.properties file to set the location of the SDK in the same way that the existing SDK requires, using the sdk.dir property.
Alternatively, you can set an environment variable called ANDROID_HOME. There is no differences between the two methods, you can use the one you prefer. Example local.properties file:
sdk.dir=/path/to/Android/Sdk
The basic build files
above expects a default folder structure. Gradle follows the concept of
convention over configuration, providing sensible default option values
when possible. The
basic project starts with two components called “source sets”, one for
the main source code and one for the test code. These live respectively
in:
- src/main/
- src/androidTest/
Inside each of these directories there are subdirectories for each source component. For both the Java and Android plugin, the location of the Java source code and the Java resources are:
For the Android plugin, extra files and folders specific to Android:
- AndroidManifest.xml
- res/
- assets/
- aidl/
- rs/
- jni/
- jniLibs/
This means that *.java files for the main source set are located in src/main/java and the main manifest is src/main/AndroidManifest.xml
Note:
src/androidTest/AndroidManifest.xml is not needed as it is created automatically.
Configuring the Structure
When the default project structure isn’t adequate, it is possible to configure it. See
this page in gradle documentation for information how this can be done for pure-java projects.
The Android plugin uses a similar syntax, but because it uses its own sourceSets, this is done within the android block. Here’s an example, using the old project structure (used in Eclipse) for the main code and remapping the androidTest sourceSet to the tests folder:
android {
sourceSets {
main {
manifest.srcFile 'AndroidManifest.xml'
java.srcDirs = ['src']
resources.srcDirs = ['src']
aidl.srcDirs = ['src']
renderscript.srcDirs = ['src']
res.srcDirs = ['res']
assets.srcDirs = ['assets']
}
androidTest.setRoot('tests')
}
}
Note: because the old structure put all source files (Java,
AIDL and RenderScript) in the same folder, we need to remap all those
new components of the sourceSet to the same src folder.
Note: setRoot() moves the whole sourceSet (and its sub folders) to a new folder. This moves src/androidTest/* to tests/* This is Android specific and will not work on Java sourceSets.
Build Tasks
General Tasks
Applying a plugin to
the build file automatically creates a set of build tasks to run. Both
the Java plugin and the Android plugin do this. The convention for tasks is the following:
- assemble
The task to assemble the output(s) of the project.
- check
The task to run all the checks.
- build
This task does both assemble and check.
- clean
This task cleans the output of the project.
The tasks assemble, check and build don’t actually do anything. They are "anchor" tasks for the plugins to add dependent tasks that actually do the work.
This allows you to always call the same task(s) no matter what the type
of project is, or what plugins are applied. For instance, applying the
findbugs plugin will create a new task and make
check depend on it, making it be called whenever the
check task is called.
From the command line you can get the high level task running the following command:
gradle tasks
For a full list and seeing dependencies between the tasks run:
gradle tasks --all
Note: Gradle automatically monitor the declared inputs and outputs of a task.
Running the build task twice without making changes to your project, will make Gradle report all tasks as UP-TO-DATE,
meaning no work was required. This allows tasks to properly depend on
each other without requiring unnecessary build operations.
Here are the two most important tasks created by the
java
plugin, dependencies of the main anchor tasks:
- assemble
- jar
This task creates the output.
- check
- test
This task runs the tests.
The
jar task itself will depend directly and indirectly on other tasks:
classes for instance will compile the Java code.
The tests are compiled with testClasses, but it is rarely useful to call this as test depends on it (as well as classes).
In general, you will probably only ever call
assemble or
check, and ignore the other tasks. You can see the full set of tasks and their descriptions for the Java plugin
here.
Android tasks
The Android plugin uses the same convention to stay compatible with other plugins, and adds an additional anchor task:
- assemble
The task to assemble the output(s) of the project.
- check
The task to run all the checks.
- connectedCheck
Runs checks that requires a connected device or emulator. they will run on all connected devices in parallel.
- deviceCheck
Runs checks using APIs to connect to remote devices. This is used on CI servers.
- build
This task does both assemble and check
- clean
This task cleans the output of the project.
The new anchor tasks are necessary in order to be able to run regular checks without needing a connected device. Note that
build does not depend on
deviceCheck, or
connectedCheck.
An Android project has at least two outputs: a debug APK and a release
APK. Each of these has its own anchor task to facilitate building them
separately:
- assemble
- assembleDebug
- assembleRelease
They both depend on other tasks that execute the multiple steps needed to build an APK. The assemble task depends on both, so calling it will build both APKs.
Tip: Gradle support camel case shortcuts for task names on the command line. For instance:
gradle aR
is the same as typing
gradle assembleRelease
as long as no other task matches ‘aR’
The check anchor tasks have their own dependencies:
- check
- connectedCheck
- deviceCheck
- This depends on tasks created when other plugins implement test extension points.
Finally, the plugin creates tasks for installing and uninstalling all build types (
debug,
release,
test), as long as they can be installed (which requires signing), e.g.
- installDebug
- installRelease
- uninstallAll
- uninstallDebug
- uninstallRelease
- uninstallDebugAndroidTest
Basic Build Customization
The Android plugin provides a broad DSL to customize most things directly from the build system.
Manifest entries
Through the DSL it is possible to configure the most important manifest entries, like these:
- minSdkVersion
- targetSdkVersion
- versionCode
- versionName
- applicationId (the effective packageName -- see ApplicationId versus PackageName for more information)
- testApplicationId (used by the test APK)
- testInstrumentationRunner
Example:
android {
compileSdkVersion 23
buildToolsVersion "23.0.1"
defaultConfig {
versionCode 12
versionName "2.0"
minSdkVersion 16
targetSdkVersion 23
}
}
The power of putting these manifest properties in the build file is that
the values can be chosen dynamically. For instance, one could be
reading the version name from a file or using other custom logic:
def computeVersionName() {
...
}
android {
compileSdkVersion 23
buildToolsVersion "23.0.1"
defaultConfig {
versionCode 12
versionName computeVersionName()
minSdkVersion 16
targetSdkVersion 23
}
}
Note: Do not use function names that could conflict with existing getters in the given scope. For instance defaultConfig { ...}
calling getVersionName()
will automatically use the getter of defaultConfig.getVersionName()
instead of the custom method.
By default, the
Android plugin automatically sets up the project to build both a debug
and a release version of the application. These
differ mostly around the ability to debug the application on a secure
(non dev) devices, and details of how the APK is signed. The
debug version is signed with a key/certificate that is created
automatically with a known name/password (to prevent required prompt
during the build). The release is not signed during the build, this
needs to happen after.
This configuration is done through an object called a BuildType. By default, 2 instances are created, a debug and a release one. The Android plugin allows customizing those two instances as well as creating other Build Types. This is done with the buildTypes DSL container:
android {
buildTypes {
debug {
applicationIdSuffix ".debug"
}
jnidebug {
initWith(buildTypes.debug)
applicationIdSuffix ".jnidebug"
jniDebuggable true
}
}
}
The above snippet achieves the following:
- Configures the default debug Build Type:
- set its package to be <app appliationId>.debug to be able to install both debug and release apk on the same device
- Creates a new BuildType called jnidebug and configure it to be a copy of the debug build type.
- Keep configuring the jnidebug, by enabling debug build of the JNI component, and add a different package suffix.
Creating new
Build Types is as easy as using a new element under the
buildTypes container, either to call
initWith() or to configure it with a closure. See the
DSL Reference for a list of all properties that can be configured on a build type.
In addition to modifying build properties,
Build Types can be used to add specific code and resources. For each Build Type, a new matching
sourceSet is created, with a default location of
src/<buildtypename>/, e.g.
src/debug/java directory can be used to add sources that will only be compiled for the debug APK.
This means the Build Type names cannot be main or androidTest (this is enforced by the plugin), and that they have to be unique.
Like any other source sets, the location of the build type source set can be relocated:
android {
sourceSets.jnidebug.setRoot('foo/jnidebug')
}
Additionally, for each
Build Type, a new
assemble<BuildTypeName> task is created, e.g.
assembleDebug. The
assembleDebug and
assembleRelease tasks have already been mentioned, and this is where they come from. When the
debug and
release Build Types are pre-created, their tasks are automatically created as well. According to this rule,
build.gradle snippet above will also generate an
assembleJnidebug task, and
assemble would be made to depend on it the same way it depends on the
assembleDebug and
assembleRelease tasks.
Tip: remember that you can type
gradle aJ to run the
assembleJnidebug task.
Possible use case:
- Permissions in debug mode only, but not in release mode
- Custom implementation for debugging
- Different resources for debug mode (for instance when a resource value is tied to the signing certificate).
The code/resources of the
BuildType are used in the following way:
- The manifest is merged into the app manifest
- The code acts as just another source folder
- The resources are overlayed over the main resources, replacing existing values.
Signing Configurations
- A keystore
- A keystore password
- A key alias name
- A key password
- The store type
The location, as well as the key name, both passwords and store type form together a
Signing Configuration. By default, there is a
debug configuration that is setup to use a debug keystore, with a known password and a default key with a known password.
The debug keystore is located in
$HOME/.android/debug.keystore, and is created if not present. The
debug Build Type is set to use this debug SigningConfig automatically.
It is possible to create other configurations or customize the default built-in one. This is done through the signingConfigs DSL container:
android {
signingConfigs {
debug {
storeFile file("debug.keystore")
}
myConfig {
storeFile file("other.keystore")
storePassword "android"
keyAlias "androiddebugkey"
keyPassword "android"
}
}
buildTypes {
foo {
signingConfig signingConfigs.myConfig
}
}
}
The above snippet changes the location of the debug keystore to be at the root of the project. This automatically impacts any Build Types that are set to using it, in this case the debug Build Type. It also creates a new Signing Config and a new Build Type that uses the new configuration.
Note: Only debug keystores located in the default location will
be automatically created. Changing the location of the debug keystore
will not create it on-demand. Creating a SigningConfig with a
different name that uses the default debug keystore location will create
it automatically. In other words, it’s tied to the location of the
keystore, not the name of the configuration.
Note: Location of keystores are usually relative to the root of
the project, but could be absolute paths, thought it is not recommended
(except for the debug one since it is automatically created).
Note: If you are checking these files into version control, you may not want the password in the file. The
following Stack Overflow post shows ways to read the values from the console, or from environment variables.
Dependencies, Android Libraries and Multi-project setup
Gradle projects can have dependencies on other components. These
components can be external binary packages, or other Gradle projects.
Dependencies on binary packages
Local packages
To configure a dependency on an external library jar, you need to add a dependency on the compile configuration. The snippet below adds a dependency on all jars inside the libs directory.
dependencies {
compile fileTree(dir: 'libs', include: ['*.jar'])
}
android {
...
}
Note: the
dependencies DSL element is part of the standard Gradle API and does not belong inside the
android element.
The
compile configuration is used to compile the main application. Everything in it is added to the compilation classpath
and also packaged in the final APK. There are other possible configurations to add dependencies to:
- compile: main application
- androidTestCompile: test application
- debugCompile: debug Build Type
- releaseCompile: release Build Type.
Because it’s not possible to build an APK that does not have an associated
Build Type, the APK is always configured with two (or more) configurations:
compile and
<buildtype>Compile.
Creating a new Build Type automatically creates a new configuration based on its name. This
can be useful if the debug version needs to use a custom library (to
report crashes for instance), while the release doesn’t, or if they rely
on different versions of the same library (see
Gradle documentation on details of how version conflicts are handled).
Remote artifacts
Gradle supports pulling artifacts from Maven and Ivy
repositories. First the repository must be added to the list, and then
the dependency must be declared in a way that Maven or Ivy declare their
artifacts.
repositories {
jcenter()
}
dependencies {
compile 'com.google.guava:guava:18.0'
}
android {
...
}
Note:
jcenter() is a shortcut to specifying the URL of the repository. Gradle supports both remote and local repositories.
Note: Gradle will
follow all dependencies transitively. This means that if a dependency
has dependencies of its own, those are pulled in as well.
For more information about setting up dependencies, read the Gradle user guide
here, and DSL documentation
here.
Multi project setup
Gradle projects can also depend on other gradle projects by using a
multi-project setup. A multi-project setup usually works by having all
the projects as sub folders of a given root project. For instance, given
to following structure:
MyProject/
+ app/
+ libraries/
+ lib1/
+ lib2/
We can identify 3 projects. Gradle will reference them with the following name:
:app
:libraries:lib1
:libraries:lib2
Each projects will have its own build.gradle declaring how it gets built. Additionally, there will be a file called settings.gradle at the root declaring the projects. This gives the following structure:
MyProject/
| settings.gradle
+ app/
| build.gradle
+ libraries/
+ lib1/
| build.gradle
+ lib2/
| build.gradle
The content of settings.gradle is very simple. It defines which folder is actually a Gradle project:
include ':app', ':libraries:lib1', ':libraries:lib2'
The :app project is likely to depend on the libraries, and this is done by declaring the following dependencies:
dependencies {
compile project(':libraries:lib1')
}
More general information about multi-project setup
here.
Library projects
In the above multi-project setup, :libraries:lib1 and :libraries:lib2 can be Java projects, and the :app Android project will use their jar output. However,
if you want to share code that accesses Android APIs or uses
Android-style resources, these libraries cannot be regular Java project,
they have to be Android Library Projects.
Creating a Library Project
A Library project is very similar to a regular Android project with
a few differences. Since building libraries is different than building
applications, a different plugin is used. Internally both plugins share
most of the same code and they are both provided by the same com.android.tools.build.gradle jar.
buildscript {
repositories {
jcenter()
}
dependencies {
classpath 'com.android.tools.build:gradle:1.3.1'
}
}
apply plugin: 'com.android.library'
android {
compileSdkVersion 23
buildToolsVersion "23.0.1"
}
This creates a library project that uses API 23 to compile.
SourceSets, build types and dependencies are handled the same as they are in an application project and can be customized the same way.
Differences between a Project and a Library Project
A Library project's main output is an
.aar package (which
stands for Android archive). It is a combination of compile code (as a
jar file and/or native .so files) and resources (manifest, res,
assets).
A library project can also generate a test apk to test the library independently from an application. The same anchor tasks are used for this (assembleDebug, assembleRelease) so there’s no difference in commands to build such a project. For
the rest, libraries behave the same as application projects. They have
build types and product flavors (see below), and can potentially
generate more than one version of the aar. Note that most of the configuration of the Build Type do not apply to library projects. However you can use the custom sourceSet to change the content of the library depending on whether it’s used by a project or being tested.
Referencing a Library
Referencing a library is done the same way any other project is referenced:
dependencies {
compile project(':libraries:lib1')
compile project(':libraries:lib2')
}
Note: if you have more than one library, then the order will
be important. This is similar to the old build system where the order
of the dependencies in the project.properties file was important.
Library Publication
By default a library only publishes its release variant.
This variant will be used by all projects referencing the library, no
matter which variant they build themselves. This is a temporary
limitation due to Gradle limitations that we are working towards
removing. You can control which variant gets published:
android {
defaultPublishConfig "debug"
}
Note that this publishing configuration name references the full variant name. Release and debug
are only applicable when there are no flavors. If you wanted to change
the default published variant while using flavors, you would write:
android {
defaultPublishConfig "flavor1Debug"
}
It is also possible to publish all
variants of a library. We are planning to allow this while using a
normal project-to-project dependency (like shown above), but this is not
possible right now due to limitations in Gradle (we are working toward
fixing those as well).
Publishing of all variants are not enabled by default. The snippet below enables this feature:
android {
publishNonDefault true
}
It is important to realize that
publishing multiple variants means publishing multiple aar files,
instead of a single aar containing multiple variants. Each aar packaging
contains a single variant. Publishing
a variant means making this aar available as an output artifact of the
Gradle project. This can then be used either when publishing to a maven
repository, or when another project creates a dependency on the library
project.
Gradle has a concept of default" artifact. This is the one that is used when writing:
dependencies {
compile project(':libraries:lib2')
}
To create a dependency on another published artifact, you need to specify which one to use:
dependencies {
flavor1Compile project(path: ':lib1', configuration: 'flavor1Release')
flavor2Compile project(path: ':lib1', configuration: 'flavor2Release')
}
Important: Note that the published configuration is a full variant, including the build type, and needs to be referenced as such.
Important: When
enabling publishing of non default, the Maven publishing plugin will
publish these additional variants as extra packages (with classifier).
This means that this is not really compatible with publishing to a maven
repository. You should either publish a single variant to a repository
OR enable all config publishing for inter-project dependencies.
Building a test application is integrated into the application project. There is no need for a separate test project anymore.
Unit testing
For the unit testing support added in 1.1, please see this separate page.
The rest of this section describes "instrumentation tests" that can run
on a real device (or an emulator) and require a separate, testing APK
to be built.
As mentioned previously, next to the main sourceSet is the androidTest sourceSet, located by default in src/androidTest/. Using this sourceSet a
test APK gets built, which can be deployed to a device to test the
application using the Android testing framework. This can contain
android unit tests, instrumentation tests, and uiautomator tests. The <instrumentation> node of the manifest for the test app is generated but you can create a src/androidTest/AndroidManifest.xml file to add other components to the test manifest.
There are a few values that can be configured for the test app, in order to configure the
<instrumentation> node (see the
DSL reference for details)
- testApplicationId
- testInstrumentationRunner
-
testHandleProfiling
-
testFunctionalTest
As seen previously, those are configured in the
defaultConfig object:
android {
defaultConfig {
testApplicationId "com.test.foo"
testInstrumentationRunner "android.test.InstrumentationTestRunner"
testHandleProfiling true
testFunctionalTest true
}
}
The value of the targetPackage attribute of the instrumentation
node in the test application manifest is automatically filled with the
package name of the tested app, even if it is customized through the defaultConfig and/or the Build Type objects. This is one of the reason this part of the manifest is generated automatically.
Additionally, the androidTest source set can be configured to
have its own dependencies. By default, the application and its own
dependencies are added to the test app classpath, but this can be
extended with the snippet below:
dependencies {
androidTestCompile 'com.google.guava:guava:11.0.2'
}
The test app is built by the assembleAndroidTest task. It is not a dependency of the main assemble task, and is instead called automatically when the tests are set to run.
Currently only one Build Type is tested. By default it is the debug Build Type, but this can be reconfigured with:
android {
...
testBuildType "staging"
}
Resolving conflicts between main and test APK
When instrumentation tests are run, both the main APK and test APK
share the same classpath. Gradle build will fail if the main APK and the
test APK use the same library (e.g. Guava) but in different versions.
If gradle didn't catch that, your app could behave differently during
tests and during normal run (including crashing in one of the cases).
To make the build succeed, just make sure both APKs use the same
version. If the error is about an indirect dependency (a library you
didn't mention in your build.gradle), just add a dependency for the
newer version to the configuration ("compile" or "androidTestCompile")
that needs it. You can also use
Gradle's resolution strategy mechanism.
You can inspect the dependency tree by running ./gradlew :app:dependencies
and
./gradlew :app:androidDependencies.
Running tests
As mentioned previously, checks requiring a connected device are launched with the anchor task called connectedCheck. This depends on the task connectedDebugAndroidTest and therefore will run it. This task does the following:
- Ensure the app and the test app are built (depending on assembleDebug and assembleDebugAndroidTest).
- Install both apps.
- Run the tests.
- Uninstall both apps.
If more than one device is connected, all tests are run in parallel on all connected devices.
If one of the test fails, on any device, the build will fail.
Testing Android Libraries
Testing Android Library project is done exactly the same way as
application projects. The only difference is that the whole library (and
its dependencies) is automatically added as a Library dependency to the
test app. The result is that the test APK includes not only its own
code, but also the library itself and all its dependencies. The manifest
of the Library is merged into the manifest of the test app (as is the
case for any project referencing this Library). The androidTest task
is changed to only install (and uninstall) the test APK (since there
are no other APK to install.) and everything else is identical.
When running unit tests, Gradle outputs an HTML report to easily look at the results. The Android plugins build on this and extends the HTML report to aggregate the results from all connected devices. All test results are stored as XML files under build/reports/androidTests/ (this is similar to regular jUnit results that are stored under build/reports/tests). This can be configured with:
android {
...
testOptions {
resultsDir = "${project.buildDir}/foo/results"
}
}
In a multi project setup with application(s) and library(ies)
projects, when running all tests at the same time, it might be useful to
generate a single reports for all tests.
To do this, a different plugin is available in the same artifact. It can be applied with:
buildscript {
repositories {
jcenter()
}
dependencies {
classpath 'com.android.tools.build:gradle:0.5.6'
}
}
apply plugin: 'android-reporting'
This should be applied to the root project, ie in build.gradle next to settings.gradle
Then from the root folder, the following command line will run all the tests and aggregate the reports:
gradle deviceCheck mergeAndroidReports --continue
Note: the
--continue
option ensure that all tests, from all sub-projects will be run even if
one of them fails. Without it the first failing test will interrupt the
run and not all projects may have their tests run.
Lint support
You can run lint for a specific variant (see below), e.g.
./gradlew lintRelease
, or for all variants (
./gradlew lint
), in which case it produces a report which describes which specific variants a given issue applies to.
You can configure lint by adding a lintOptions section like following. You typically only specify a few of these, see the DSL reference for all available options.
android {
lintOptions {
// turn off checking the given issue id's
disable 'TypographyFractions','TypographyQuotes'
// turn on the given issue id's
enable 'RtlHardcoded','RtlCompat', 'RtlEnabled'
// check *only* the given issue id's
check 'NewApi', 'InlinedApi'
}
}
One goal of the new build system is to enable creating different versions of the same application.
There are two main use cases:
- Different versions of the same application
For instance, a free/demo version vs the “pro” paid application.
- Same application packaged differently for multi-apk in Google Play Store.
See http://developer.android.com/google/play/publishing/multiple-apks.html for more information.
- A combination of 1. and 2.
The goal was to be able to generate these different APKs from the same
project, as opposed to using a single Library Projects and 2+
Application Projects.
Product flavors
A product flavor defines a customized version of the application
build by the project. A single project can have different flavors which
change the generated application.
This new concept is designed to help when the differences are very
minimum. If the answer to “Is this the same application?” is yes, then
this is probably the way to go over Library Projects.
Product flavors are declared using a productFlavors DSL container:
android {
....
productFlavors {
flavor1 {
...
}
flavor2 {
...
}
}
}
This creates two flavors, called flavor1 and flavor2.
Note: The name of the flavors cannot collide with existing
Build Type names, or with the
androidTest and
test source sets.
Build Type + Product Flavor = Build Variant
As we have seen before, each
Build Type generates a new APK.
Product Flavors do the same: the output of the project becomes all possible combinations of
Build Types and, if applicable,
Product Flavors. Each (
Build Type,
Product Flavor) combination is called a
Build Variant. For instance, with the default
debug and
release Build Types, the above example generates four
Build Variants:
- Flavor1 - debug
- Flavor1 - release
- Flavor2 - debug
- Flavor2 - release
Projects with no flavors still have
Build Variants, but the single
default flavor/config is used, nameless, making the list of variants similar to the list of
Build Types.
Product Flavor Configuration
Each flavors is configured with a closure:
android {
...
defaultConfig {
minSdkVersion 8
versionCode 10
}
productFlavors {
flavor1 {
applicationId "com.example.flavor1"
versionCode 20
}
flavor2 {
applicationId "com.example.flavor2"
minSdkVersion 14
}
}
}
Note that the
android.productFlavors.* objects are of type
ProductFlavor which is the same type as the
android.defaultConfig object. This means they share the same properties.
defaultConfig
provides the base configuration for all flavors and each flavor can
override any value. In the example above, the configurations end up
being:
- flavor1
- applicationId: com.example.flavor1
- minSdkVersion: 8
- versionCode: 20
- flavor2
- applicationId: com.example.flavor2
- minSdkVersion: 14
- versionCode: 10
Usually, the
Build Type configuration is an overlay over the other configuration. For instance, the
Build Type's
applicationIdSuffix is appended to the
Product Flavor's
applicationId. There are cases where a setting is settable on both the
Build Type and the
Product Flavor. In this case, it’s is on a case by case basis. For instance,
signingConfig is one of these properties. This enables either having all release packages share the same S
igningConfig, by setting
android.buildTypes.release.signingConfig, or have each release package use their own S
igningConfig by setting each
android.productFlavors.*.signingConfig objects separately.
Sourcesets and Dependencies
Similar to
Build Types,
Product Flavors also contribute code and resources through their own
sourceSets. The above example creates four
sourceSets:
- android.sourceSets.flavor1
Location src/flavor1/
- android.sourceSets.flavor2
Location src/flavor2/
- android.sourceSets.androidTestFlavor1
Location src/androidTestFlavor1/
- android.sourceSets.androidTestFlavor2
Location src/androidTestFlavor2/
Those
sourceSets are used to build the APK, alongside
android.sourceSets.main and the
Build Type sourceSet. The following rules are used when dealing with all the sourcesets used to build a single APK:
- All source code (src/*/java) are used together as multiple folders generating a single output.
- Manifests are all merged together into a single manifest. This allows Product Flavors to have different components and/or permissions, similarly to Build Types.
- All resources (Android res and assets) are used using overlay priority where the Build Type overrides the Product Flavor, which overrides the main sourceSet.
- Each Build Variant generates its own R class (or other generated source code) from the resources. Nothing is shared between variants.
Finally, like Build Types, Product Flavors can have
their own dependencies. For instance, if the flavors are used to
generate a ads-based app and a paid app, one of the flavors could have a
dependency on an Ads SDK, while the other does not.
dependencies {
flavor1Compile "..."
}
In this particular case, the file src/flavor1/AndroidManifest.xml would probably need to include the internet permission.
Additional sourcesets are also created for each variants:
- android.sourceSets.flavor1Debug
Location src/flavor1Debug/
- android.sourceSets.flavor1Release
Location src/flavor1Release/
- android.sourceSets.flavor2Debug
Location src/flavor2Debug/
- android.sourceSets.flavor2Release
Location src/flavor2Release/
These have higher priority than the build type sourcesets, and allow customization at the variant level.
Building and Tasks
We previously saw that each
Build Type creates its own
assemble<name> task, but that
Build Variants are a combination of
Build Type and
Product Flavor.
When
Product Flavors are used, more assemble-type tasks are created. These are:
- assemble<Variant Name>
- assemble<Build Type Name>
- assemble<Product Flavor Name>
#1 allows directly building a single variant. For instance
assembleFlavor1Debug.
#2 allows building all APKs for a given Build Type. For instance
assembleDebug will build both
Flavor1Debug and
Flavor2Debug variants.
#3 allows building all APKs for a given flavor. For instance
assembleFlavor1 will build both
Flavor1Debug and
Flavor1Release variants.
The task
assemble will build all possible variants.
In some case, one may want to create several versions of the same apps based on more than one criteria.
For instance, multi-apk support in Google Play supports 4 different
filters. Creating different APKs split on each filter requires being
able to use more than one dimension of Product Flavors.
Consider the example of a game that has a demo and a paid version and
wants to use the ABI filter in the multi-apk support. With 3 ABIs and
two versions of the application, 6 APKs needs to be generated (not
counting the variants introduced by the different Build Types).
However, the code of the paid version is the same for all three ABIs, so creating simply 6 flavors is not the way to go.
Instead, there are two dimensions of flavors, and variants should automatically build all possible combinations.
This feature is implemented using Flavor Dimensions. Flavors are assigned to a specific dimension:
android {
...
flavorDimensions "abi", "version"
productFlavors {
freeapp {
dimension "version"
...
}
paidapp {
dimension "version"
...
}
arm {
dimension "abi"
...
}
mips {
dimension "abi"
...
}
x86 {
dimension "abi"
...
}
}
}
The
android.flavorDimensions array defines the possible dimensions, as well as the order. Each defined
Product Flavor is assigned to a dimension.
From the following dimensioned
Product Flavors [freeapp, paidapp] and [x86, arm, mips] and the [debug, release]
Build Types, the following build variants will be created:
- x86-freeapp-debug
- x86-freeapp-release
- arm-freeapp-debug
- arm-freeapp-release
- mips-freeapp-debug
- mips-freeapp-release
- x86-paidapp-debug
- x86-paidapp-release
- arm-paidapp-debug
- arm-paidapp-release
- mips-paidapp-debug
- mips-paidapp-release
The order of the dimension as defined by
android.flavorDimensions is very important.
Each variant is configured by several
Product Flavor objects:
- android.defaultConfig
- One from the abi dimension
- One from the version dimension
The order of the dimension drives which flavor override the other, which
is important for resources when a value in a flavor replaces a value
defined in a lower priority flavor.
The flavor dimension is defined with higher priority first. So in this case:
abi > version > defaultConfig
Multi-flavors projects also have additional sourcesets, similar to the variant sourcesets but without the build type:
- android.sourceSets.x86Freeapp
Location src/x86Freeapp/
- android.sourceSets.armPaidapp
Location src/armPaidapp/
- etc...
These allow
customization at the flavor-combination level. They have higher priority
than the basic flavor sourcesets, but lower priority than the build
type sourcesets.
Testing
Testing multi-flavors project is very similar to simpler projects.
The
androidTest sourceset is used for common tests across all flavors, while each flavor can also have its own tests.
As mentioned above,
sourceSets to test each flavor are created:
- android.sourceSets.androidTestFlavor1
Location src/androidTestFlavor1/
- android.sourceSets.androidTestFlavor2
Location src/androidTestFlavor2/
Similarly, those can have their own dependencies:
dependencies {
androidTestFlavor1Compile "..."
}
Running the tests can be done through the main
deviceCheck anchor task, or the main
androidTest tasks which acts as an anchor task when flavors are used.
Each flavor has its own task to run tests:
androidTest<VariantName>. For instance:
- androidTestFlavor1Debug
- androidTestFlavor2Debug
Similarly, test APK building tasks and install/uninstall tasks are per variant:
- assembleFlavor1Test
- installFlavor1Debug
- installFlavor1Test
- uninstallFlavor1Debug
- ...
Finally the HTML report generation supports aggregation by flavor.
The location of the test results and reports is as follows, first for the per flavor version, and then for the aggregated one:
- build/androidTest-results/flavors/<FlavorName>
- build/androidTest-results/all/
- build/reports/androidTests/flavors<FlavorName>
- build/reports/androidTests/all/
Customizing either path, will only change the root folder and still
create sub folders per-flavor and aggregated results/reports.
BuildConfig
At compilation time, Android Studio generates a class called BuildConfig
that contains constant values used when building a particular variant.
You can inspect the values of these constants to change behavior in
different variants, e.g.:
private void javaCode() {
if (BuildConfig.FLAVOR.equals("paidapp")) {
doIt();
else {
showOnlyInPaidAppDialog();
}
}
Here are the values that BuildConfig contains:
boolean DEBUG
– if the build is debuggable.
int VERSION_CODE
String VERSION_NAME
String APPLICATION_ID
String BUILD_TYPE
– name of the build type, e.g. "release"
String FLAVOR
– name of the flavor, e.g. "paidapp"
If the project uses flavor dimensions, additional values are generated. Using the example above, here's an example BuildConfig:
String FLAVOR = "armFreeapp"
String FLAVOR_abi = "arm"
String FLAVOR_version = "freeapp"
Filtering Variants
When you add dimensions and flavors, you can end up with variants
that don't make sense. For example you may define a flavor that uses
your Web API and a flavor that uses hard-coded fake data, for faster
testing. The second flavor is only useful for development, but not in
release builds. You can remove this variant using the variantFilter
closure, like this:
android {
productFlavors {
realData
fakeData
}
variantFilter { variant ->
def names = variant.flavors*.name
if (names.contains("fakeData") && variant.buildType.name == "release") {
variant.ignore = true
}
}
}
With the configuration above, your project will have only three variants:
realDataDebug
realDataRelease
fakeDataDebug
See the
DSL reference for all properties of
variant
that you can check.
Advanced Build Customization
Running ProGuard
The ProGuard plugin is applied automatically by the Android plugin, and the tasks are created automatically if the Build Type is configured to run ProGuard through the minifyEnabled property.
android {
buildTypes {
release {
minifyEnabled true
proguardFile getDefaultProguardFile('proguard-android.txt')
}
}
productFlavors {
flavor1 {
}
flavor2 {
proguardFile 'some-other-rules.txt'
}
}
Variants use all the rules files declared in their build type, and product flavors.
There are 2 default rules files
- proguard-android.txt
- proguard-android-optimize.txt
They are located in the SDK. Using getDefaultProguardFile() will return the full path to the files. They are identical except for enabling optimizations.
Shrinking Resources
You can also remove unused resources, automatically, at build time. For more information, see the
Resource Shrinking document.
Manipulating tasks
Basic Java projects have a finite set of tasks that all work together to create an output.
The
classes task is the one that compile the Java source code.
It’s easy to access from
build.gradle by simply using
classes in a script. This is a shortcut for
project.tasks.classes.
In Android projects, this is a bit more complicated because there could
be a large number of the same task and their name is generated based on
the
Build Types and
Product Flavors.
In order to fix this, the
android object has two properties:
- applicationVariants (only for the app plugin)
- libraryVariants (only for the library plugin)
- testVariants (for both plugins)
All three return a
DomainObjectCollection of
ApplicationVariant,
LibraryVariant, and
TestVariant objects respectively.
Note that accessing any of these collections will trigger the creations
of all the tasks. This means no (re)configuration should take place
after accessing the collections.
The
DomainObjectCollection gives access to all the objects directly, or through filters which can be convenient.
android.applicationVariants.all { variant ->
....
}
All three variant classes share the following properties:
Property Name |
Property Type |
Description |
name |
String |
The name of the variant. Guaranteed to be unique. |
description |
String |
Human readable description of the variant. |
dirName |
String |
subfolder name for the variant. Guaranteed to be unique. Maybe more than one folder, ie “debug/flavor1” |
baseName |
String |
Base name of the output(s) of the variant. Guaranteed to be unique. |
outputFile |
File |
The output of the variant. This is a read/write property |
processManifest |
ProcessManifest |
The task that processes the manifest. |
aidlCompile |
AidlCompile |
The task that compiles the AIDL files. |
renderscriptCompile |
RenderscriptCompile |
The task that compiles the Renderscript files. |
mergeResources |
MergeResources |
The task that merges the resources. |
mergeAssets |
MergeAssets |
The task that merges the assets. |
processResources |
ProcessAndroidResources |
The task that processes and compile the Resources. |
generateBuildConfig |
GenerateBuildConfig |
The task that generates the BuildConfig class. |
javaCompile |
JavaCompile |
The task that compiles the Java code. |
processJavaResources |
Copy |
The task that process the Java resources. |
assemble |
DefaultTask |
The assemble anchor task for this variant. |
The
ApplicationVariant class adds the following:
Property Name |
Property Type |
Description |
buildType |
BuildType |
The BuildType of the variant. |
productFlavors |
List<ProductFlavor> |
The ProductFlavors of the variant. Always non Null but could be empty. |
mergedFlavor |
ProductFlavor |
The merging of android.defaultConfig and variant.productFlavors |
signingConfig |
SigningConfig |
The SigningConfig object used by this variant |
isSigningReady |
boolean |
true if the variant has all the information needed to be signed. |
testVariant |
BuildVariant |
The TestVariant that will test this variant. |
dex |
Dex |
The task that dex the code. Can be null if the variant is a library. |
packageApplication |
PackageApplication |
The task that makes the final APK. Can be null if the variant is a library. |
zipAlign |
ZipAlign |
The task that zipaligns the apk. Can be null if the variant is a library or if the APK cannot be signed. |
install |
DefaultTask |
The installation task. Can be null. |
uninstall |
DefaultTask |
The uninstallation task. |
The
LibraryVariant class adds the following:
Property Name |
Property Type |
Description |
buildType |
BuildType |
The BuildType of the variant. |
mergedFlavor |
ProductFlavor |
The defaultConfig values |
testVariant |
BuildVariant |
The Build Variant that will test this variant. |
packageLibrary |
Zip |
The task that packages the Library AAR archive. Null if not a library. |
The
TestVariant class adds the following:
Property Name |
Property Type |
Description |
buildType |
BuildType |
The BuildType of the variant. |
productFlavors |
List<ProductFlavor> |
The ProductFlavors of the variant. Always non Null but could be empty. |
mergedFlavor |
ProductFlavor |
The merging of android.defaultConfig and variant.productFlavors |
signingConfig |
SigningConfig |
The SigningConfig object used by this variant |
isSigningReady |
boolean |
true if the variant has all the information needed to be signed. |
testedVariant |
BaseVariant |
The BaseVariant that is tested by this TestVariant. |
dex |
Dex |
The task that dex the code. Can be null if the variant is a library. |
packageApplication |
PackageApplication |
The task that makes the final APK. Can be null if the variant is a library. |
zipAlign |
ZipAlign |
The task that zipaligns the apk. Can be null if the variant is a library or if the APK cannot be signed. |
install |
DefaultTask |
The installation task. Can be null. |
uninstall |
DefaultTask |
The uninstallation task. |
connectedAndroidTest |
DefaultTask |
The task that runs the android tests on connected devices. |
providerAndroidTest |
DefaultTask |
The task that runs the android tests using the extension API.
|
API for Android specific task types.
- ProcessManifest
- AidlCompile
- RenderscriptCompile
- File sourceOutputDir
- File resOutputDir
- MergeResources
- MergeAssets
- ProcessAndroidResources
- File manifestFile
- File resDir
- File assetsDir
- File sourceOutputDir
- File textSymbolOutputDir
- File packageOutputFile
- File proguardOutputFile
- GenerateBuildConfig
- Dex
- PackageApplication
- File resourceFile
- File dexFile
- File javaResourceDir
- File jniDir
- File outputFile
- To change the final output file use "outputFile" on the variant object directly.
- ZipAlign
- File inputFile
- File outputFile
- To change the final output file use "outputFile" on the variant object directly.
The API for each task type is limited due to both how Gradle works and how the Android plugin sets them up.
First, Gradle is meant to have the tasks be only configured for
input/output location and possible optional flags. So here, the tasks
only define (some of) the inputs/outputs.
Second, the input for most of those tasks is non-trivial, often coming from mixing values from the sourceSets, the Build Types, and the Product Flavors.
To keep build files simple to read and understand, the goal is to let
developers modify the build by tweak these objects through the DSL,
rather than diving deep in the inputs and options of the tasks and
changing them.
Also note, that except for the ZipAlign task type, all other types
require setting up private data to make them work. This means it’s not
possible to manually create new tasks of these types.
This API is subject to change. In general the current API is around
giving access to the outputs and inputs (when possible) of the tasks to
add extra processing when required). Feedback is appreciated, especially
around needs that may not have been foreseen.
For Gradle tasks (DefaultTask, JavaCompile, Copy, Zip), refer to the Gradle documentation.
Setting language level
You can use the compileOptions
block to choose the language level used by the compiler. The default is chosen based on the compileSdkVersion
value.
android {
compileOptions {
sourceCompatibility JavaVersion.VERSION_1_6
targetCompatibility JavaVersion.VERSION_1_6
}
}