Android gradle build: how to set global variables - gradle

Question

How can I set a global variable that can be accessed from build.gradle and tasks?

Answer 1

To set a global variable
project.ext.set("variableName", value)
To access it from anywhere in the project:
project.variableName
For instance:
project.ext.set("newVersionName", versionString)
and then...
println project.newVersionName
For more information see: http://www.gradle.org/docs/current/dsl/org.gradle.api.plugins.ExtraPropertiesExtension.html
EDIT:
As commented by Dmitry, In new versions you can use the following shorthand:
project.ext.variableName = value

Answer 2

The answer from Guy is excellent. I just want to add the practical code.
Example:
Put something like this in the Project build.gradle:
project.ext {
minSdkVersion = 21
targetSdkVersion = 23
}
And put something like this in the Module build.gradle to access it:
defaultConfig {
minSdkVersion.apiLevel project.minSdkVersion
targetSdkVersion.apiLevel project.targetSdkVersion
}

Answer 3

You can also do this. Let's say you want to add appcompat with the version 25.3.1, you can add a variable version_name in your project level build.gradle.
buildscript{
ext.version_name = '25.3.1'
}
Now you can add this to your application level build gradle and avoid any conflicts.
compile "com.android.support:appcompat-v7:$version_name"
compile "com.android.support:recyclerview-v7:$version_name"
compile "com.android.support:design:$version_name"

Answer 4

You cant create a Gradle file in the project's root directory and put all variables there, like this:
lib-versions.gradle
ext {
kt_core = '1.6.0'
app_compat = '1.3.1'
material = '1.4.0'
constraintlayout = '2.1.1'
nav_version = '2.3.5'
junit = '4.13.2'
junit_ext = '1.1.3'
escpresso = '3.4.0'
}
Then in the project build.gradle file on the bottom you should apply the Gradle file like this:
buildscript {
...
}
task clean(type: Delete) {
delete rootProject.buildDir
}
apply from: 'lib-versions.gradle' //apply it like this
Then you are able to use the variables in any module-level build Gradle file (app/build.gradle) like this:
implementation "androidx.core:core-ktx:$rootProject.ext.kt_core"
implementation "androidx.appcompat:appcompat:$rootProject.ext.app_compat"
implementation "com.google.android.material:material:$rootProject.ext.material"
implementation "androidx.constraintlayout:constraintlayout:$rootProject.ext.constraintlayout"
...

Answer 5

Additional, for dynamic global variables you can define global functions in the master build.gradle file:
First, define your function, for example for git branch:
def getGitBranch = { ->
def stdout = new ByteArrayOutputStream()
exec {
commandLine 'git', 'rev-parse', '--abbrev-ref', 'HEAD'
standardOutput = stdout
}
return stdout.toString().trim()
}
In allProjects section set the variable:
allprojects {
repositories {
google()
jcenter()
}
project.ext {
gitBranch="\"${getGitBranch()}\""
}
}
In your build.gradle files of your sub projects or android modules, get this variable like this:
android {
compileSdkVersion project.mCompileSdkVersion.toInteger()
defaultConfig {
minSdkVersion project.mMinSdkVersion.toInteger()
...
buildConfigField "String", "GitBranch", project.gitBranch
}
...
}
Finally, you can use it in your code like this:
public static String getGitBranch() {
return BuildConfig.GitBranch;
}

Answer 6

This is for Kotlin DSL (build.gradle.kts).
Root (top-level) build file:
val myVariable by extra("watermelon")
// Alternative notations:
// extra.set("myVariable", "watermelon")
// extra["myVariable"] = "watermelon"
Extra properties on a project object are visible from its subprojects. Note that extra. is equivalent to project.extra.; in other words the project object is implicit.
A sub-project build file:
val myVariable: String by rootProject.extra
// Alternative notations:
// val myVariable: String by rootProject
// val myVariable: String = rootProject.extra["myVariable"] as String
// val myVariable: String = rootProject.extra.get("myVariable") as String
Note that when using Kotlin delegation (by keyword) the name of the variables should be the same in both build files.
See Gradle Docs: Extra properties for more information.