刚开始使用 Android Studio 结果发布时不混淆代码,已经在设置里面配置了 proguardFile ,但发布时还是没有混淆代码,也没有生成mapping.txt文件.
从网上搜索出来的全是

buildTypes {
release {
runProguard true
proguardFile ‘proguard-rules.txt’
}

增加了 runProguard true 后直接报如下错误:
Error:(41, 0) Gradle DSL method not found: ‘runProguard()’
Possible causes:

• The project ‘Cardboard’ may be using a version of Gradle that does not contain the method.
  Gradle settings
• The build file may be missing a Gradle plugin.
  Apply Gradle plugin

无奈跑到 Android Tools Project Site 翻文档发现0.14.0 (2014/10/31) runProguard 改名成了 minifyEnabled ,照着操作就可以了.

参考:
http://tools.android.com/tech-docs/new-build-system
http://tools.android.com/tech-docs/new-build-system/user-guide
http://developer.android.com/tools/help/proguard.html