Android Build Constants Plugin

A Gradle plugin for Android which generates both Java and XML constants as part of the build process.

Why do I need this?

In short: To define constants that are accessible from everywhere in your Android app.

In long: There are two ways to define constants in Android. Both have their limitations.

• Creating constants using buildConfigField only adds entries to BuildConfig.java which means you cannot access them via XML.
• Creating a custom constants.xml resource file with entries like <string name="constant">constant_value</string> lets you easily reference the constant via @string/constant in XML, but requires you to have a Context object on the Java side to get the value using getResources().getString(R.string.constant).

None of the above solutions is ideal. This plugin lets you specify constants in your build.gradle file that will be translated into both a Java and an XML-based version with the same constant value.

How does it work?

The plugin creates a new task per build type, e.g. generateDebugBuildConstants. It hooks into the build process ahead of the processDebugResources task so it will be executed every time you assemble your project. It supports incremental builds, i.e. if none of the inputs or outputs have changed, Gradle can skip the task (up-to-date).

Usage

The plugin currently supports Integer, Boolean and String data types.

You can specify the constants using a closure in your build.gradle file like this:

buildConstants {
  constants {
    aBoolean = true
    aString = 'string'
    aNumber = 123
  }
}

The plugin will then generate both a Java and an XML version of the constants like so:

Java:

public final class BuildConstants {
  
  public static final boolean ABOOLEAN = true;
  public static final String ASTRING = "string";
  public static final int ANUMBER = 123;
  
  private BuildConstants() {
    throw new AssertionError("No instances.");
  }
}

XML:

<resources>
 <bool name="aboolean">true</bool>
 <string name="astring">string</string>
 <integer name="anumber">123</integer>
</resources>

Alternatively, you can define the constants using a map:

buildConstants {
  constants = [
    aBoolean : true,
    aString : 'string',
    aNumber : 123
  ]
}

Or specify just a single constant (similar to buildConfigField):

buildConstants {
  constant 'single_constant', 'single_string'
}

The default generated file names are BuildConstants.java and build_constants.xml. You can change them like this:

buildConstants {
  javaFileName 'SampleBuildConstants'
  xmlFileName 'sample_build_constants'
}

Example

Check out the sample project for an example implementation.

Download

Build script snippet for use in all Gradle versions:

buildscript {
  repositories {
    maven {
      url 'https://plugins.gradle.org/m2/'
    }
  }
  dependencies {
    classpath 'gradle.plugin.com.jenzz:buildconstants:1.1.0'
  }
}

apply plugin: 'com.jenzz.buildconstants'

Build script snippet for new, incubating, plugin mechanism introduced in Gradle 2.1:

plugins {
  id 'com.jenzz.buildconstants' version '1.1.0'
}

License

This project is licensed under the MIT License.