Android Studio and Gradle - build fails

Question

I am building a small library project along wit a sample project to illustrate the use. I can't manage to run the sample in Android Studio. I have created the project from scratch. I am experienced with Eclipse but it's my first try at Android Studio & Gradle.

The error given:

Gradle: Execution failed for task ':demo:dexDebug'.

Running C:\DevTools\Android\android-studio\sdk\build-tools\android-4.2.2\dx.bat failed. See output

I have the following folder structure:

- demo
  - build
  - libs
    - android-support-v4.jar
  - src
    - main
      - java
      - res
  - build.gradle
- library
  - build
  - libs
    - android-support-v4.jar
  - src
    - main
      - java
      - res
  - build.gradle
- build.gradle
- settings.gradle

Build.gradle at project root:

// Top-level build file where you can add configuration options common to all sub-projects/modules.

Settings.gradle at project root:

include ':library', ':demo'

Build.gradle for the library module:

buildscript {
    repositories {
        mavenCentral()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:0.4'
    }
}
apply plugin: 'android-library'

dependencies {
    compile files('libs/android-support-v4.jar')
}

android {
    compileSdkVersion 17
    buildToolsVersion "17.0.0"

    defaultConfig {
        minSdkVersion 7
        targetSdkVersion 16
    }
}

Build.gradle for the sample module:

buildscript {
    repositories {
        mavenCentral() 
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:0.4'
    }
}
apply plugin: 'android'

dependencies {
    compile project(':library')
    compile files('libs/android-support-v4.jar')
}

android {
    compileSdkVersion 17
    buildToolsVersion "17.0.0"

    defaultConfig {
        minSdkVersion 7
        targetSdkVersion 16
    }
}

Answer 1

Specifying compile files('libs/android-support-v4.jar') means that every library includes support v4. What you want to do is just specify that every library depends on it:

dependencies {
    compile 'com.android.support:support-v4:13.0.0'
}

This will allow gradle to detect all dependencies and include this only once.

Note: You have to first use the SDK Manager and download and install two Maven repositories: "Android Support Repository" and "Google Repository".

Answer 2

I found the problem:

I removed that line from the sample gradle file.

compile files('libs/android-support-v4.jar')

However, I have no idea why this does not work (if I have 2 or 3 external libraries that all depend on the support library, how are we supposed to do, without touching their gradle files?