1.在需要混淆的工程目录下(package/apps/下的工程)添加proguard.flags文件，该文件即为网络传说中的proguard.cfg，只是命名不一样而已，然后再Android.mk中添加如下两句：
LOCAL_PROGUARD_ENABLED := full
LOCAL_PROGUARD_FLAG_FILES := proguard.flags
上面的full 也可以是custom，如果不写这句，那还得添加如下一句：
TARGET_BUILD_VARIANT := user或者TARGET_BUILD_VARIANT := userdebug
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这样后在工程目录下执行mm便可以看到在out/target/common/obj/APPS/目录下生成了形如proguard.classes.jar的东东，这就说明已在编译中启动了proguard
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但反编译一看，并未出现网络云说的abcd替代符号，其实代码并未真正混淆：
android在编译时默认关闭了混淆选项，有去研究build/core目录的同志会发现这里也有个proguard.flags文件，其实在 proguard的过程中，编译器会调用包括本地目录下和系统定义了的多个proguard.flags文件，而在这个文件中混淆的选项被禁止了，故而编 译出来的apk仍未混淆。因此将如下句子注释掉便可实现真正的混淆编译：
# Don't obfuscate. We only need dead code striping.
-dontobfuscate（将该句加个#号注释掉）
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2.proguard.flags的源码如下：
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-optimizationpasses 5????
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-dontusemixedcaseclassnames????
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-dontskipnonpubliclibraryclasses????
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-dontpreverify????
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-verbose????
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-optimizations !code/simplification/arithmetic,!field/*,!class/merging/*????
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-keep public class * extends Android.app.Activity????
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-keep public class * extends android.app.Application????
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-keep public class * extends android.app.Service????
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-keep public class * extends android.content.BroadcastReceiver????
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-keep public class * extends android.content.ContentProvider????
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-keep public class * extends android.app.backup.BackupAgentHelper????
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-keep public class * extends android.preference.Preference????
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-keep public class com.android.vending.licensing.ILicensingService????
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-keepclasseswithmembernames class * {????
native <methods>;????
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?}???????
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-keepclasseswithmembers class * {????
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public <init>(android.content.Context, android.util.AttributeSet);????
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}??????
-keepclasseswithmembers class * {????
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public <init>(android.content.Context, android.util.AttributeSet, int);????
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}????
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-keepclassmembers class * extends android.app.Activity {????
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public void *(android.view.View);????
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?}????
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-keepclassmembers enum * {????
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public static **[] values();????
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public static ** valueOf(java.lang.String);????
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}??????
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-keep class * implements android.os.Parcelable {????
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public static final android.os.Parcelable$Creator *;????
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}
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3 。好奇的同志还可以继续看看，为什么TARGET_BUILD_VARIANT := user和LOCAL_PROGUARD_ENABLED := full二选一即可，详见build/core/package.mk:
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LOCAL_PROGUARD_ENABLED:=$(strip $(LOCAL_PROGUARD_ENABLED))
ifndef LOCAL_PROGUARD_ENABLED
ifneq ($(filter user userdebug, $(TARGET_BUILD_VARIANT)),)
? ? # turn on Proguard by default for user & userdebug build
? ? LOCAL_PROGUARD_ENABLED :=full
endif
endif
ifeq ($(LOCAL_PROGUARD_ENABLED),disabled)
? ? # the package explicitly request to disable proguard.
? ? LOCAL_PROGUARD_ENABLED :=
endif
proguard_options_file :=
ifneq ($(LOCAL_PROGUARD_ENABLED),custom)
ifneq ($(all_resources),)
? ? proguard_options_file := $(package_expected_intermediates_COMMON)/proguard_options
endif # all_resources
endif # !custom
LOCAL_PROGUARD_FLAGS := $(addprefix -include ,$(proguard_options_file)) $(LOCAL_PROGUARD_FLAGS)