Android with Gradle and Proguard

Question

I'm just created a new Android Library project using Gradle and would like the code to be optimized and obfuscated with via Proguard.

Here is the android portion the build.gradle file:

android {
    compileSdkVersion 19
    buildToolsVersion "19.0.1"

    defaultConfig {
        minSdkVersion 14
        targetSdkVersion 19
        versionCode 1
        versionName "1.0"
    }
    release {
        runProguard true
        proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.txt'
    }
}

When I run the gradle build command from terminal it fails at :library:proguardRelease with the message:

* What went wrong:
Execution failed for task ':library:proguardRelease'.
> java.io.IOException: The output jar is empty. Did you specify the proper '-keep' options?

Does anybody know why this is?

Gradle 1.10 JVM 1.6.0_65 Progruard 4.10

Answer 1

The following build.gradle file works for me with Proguard when executing gradlew assembleRelease.

Note it is set up to read the release keystore info from a config file (and I've included the debug key cert in the project, since its needed for Maps API v2 in debug mode), and passwords from the command line:

apply plugin: 'android'

android {
    compileSdkVersion 19
    buildToolsVersion "19.0.0"

    defaultConfig {
        minSdkVersion 8
        targetSdkVersion 19
    }

    if (project.hasProperty("secure.properties")
            && new File(project.property("secure.properties")).exists()) {

        Properties props = new Properties()
        props.load(new FileInputStream(file(project.property("secure.properties"))))

        signingConfigs {
            debug {
                storeFile file("gpstest.debug.keystore")
            }

            release {
                storeFile file(props['key.store'])
                keyAlias props['key.alias']
                storePassword "askmelater"
                keyPassword "askmelater"
            }
        }
    } else {
        signingConfigs {
            debug {
                storeFile file("gpstest.debug.keystore")
            }

            release {
                // Nothing here
            }
        }
    }

    buildTypes {
        release {
            runProguard true
            proguardFile 'proguard.cfg'
            signingConfig signingConfigs.release
        }
    } 
}

task askForPasswords << {
    // Must create String because System.readPassword() returns char[]
    // (and assigning that below fails silently)
    def storePw = new String(System.console().readPassword("\nKeystore password: "))
    def keyPw = new String(System.console().readPassword("Key password: "))

    android.signingConfigs.release.storePassword = storePw
    android.signingConfigs.release.keyPassword = keyPw
}

tasks.whenTaskAdded { theTask ->
    if (theTask.name.equals("packageRelease")) {
        theTask.dependsOn "askForPasswords"
    }
}

dependencies {
    compile project(':ShowcaseViewLibrary')
    compile 'com.google.android.gms:play-services:3.2.65'
    compile 'com.actionbarsherlock:actionbarsherlock:4.4.0@aar'
    compile 'org.jraf:android-switch-backport:1.2'
    compile 'com.google.maps.android:android-maps-utils:0.2.1'
}

Here are the instructions to set up the config files to read keystore info:

To build a release build, you need to create a "gradle.properties" file that points to a "secure.properties" file, and a "secure.properties" file that points to your keystore and alias. The gradlew assembleRelease command will prompt for your keystore passphrase.

The "gradle.properties" file is located in the GPSTest directory and has the contents:

secure.properties=<full_path_to_secure_properties_file>

The "secure.properties" file (in the location specified in gradle.properties) has the contents:

key.store=<full_path_to_keystore_file>

key.alias=<key_alias_name>

Note that the paths in these files always use the Unix path separator /, even on Windows. If you use the Windows path separator \ you will get the error No value has been specified for property 'signingConfig.keyAlias'.

Here's the path to the file/project on Github if you want to clone and test it yourself: https://github.com/barbeau/gpstest/blob/master/GPSTest/build.gradle

proguard.cfg is also in the GPSTest subdirectory (same directory as build.gradle): https://github.com/barbeau/gpstest/blob/master/GPSTest/proguard.cfg