-keepnames class com.packagename.ClassName$* {
 public <fields>;
 public <methods>;
}

这种方式可以禁止混淆内部类。

在build.gradle中进行配置

android {
    buildTypes {
        release {
            minifyEnabled true
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

##--- For:android默认 ---
-optimizationpasses 5  # 指定代码的压缩级别
-allowaccessmodification #优化时允许访问并修改有修饰符的类和类的成员
-dontusemixedcaseclassnames  # 是否使用大小写混合
-dontskipnonpubliclibraryclasses  # 是否混淆第三方jar
-dontpreverify  # 混淆时是否做预校验
-verbose    # 混淆时是否记录日志
-ignorewarnings  # 忽略警告，避免打包时某些警告出现
-optimizations !code/simplification/arithmetic,!code/simplification/cast,!field/*,!class/merging/*  # 混淆时所采用的算法

-keepattributes *Annotation*
-keep public class com.google.vending.licensing.ILicensingService
-keep public class com.android.vending.licensing.ILicensingService
-keepclasseswithmembernames class * { # 保持 native 方法不被混淆
    native <methods>;
}

-keepclassmembers public class * extends android.view.View {
   void set*(***);
   *** get*();
}

-keepclassmembers class * extends android.app.Activity {
   public void *(android.view.View);
}

-keepclassmembers enum * {  # 保持枚举 enum 类不被混淆
    public static **[] values();
    public static ** valueOf(java.lang.String);
}

-keep class * implements android.os.Parcelable { # 保持 Parcelable 不被混淆
  public static final android.os.Parcelable$Creator *;
}

-keepclassmembers class **.R$* { #不混淆R文件
    public static <fields>;
}

-dontwarn android.support.**
##--- End android默认 ---

##--- For:不能被混淆的 ---
-keep public class * extends android.app.Activity
-keep public class * extends android.app.Fragment
-keep public class * extends android.app.Application
-keep public class * extends android.app.Service
-keep public class * extends android.content.BroadcastReceiver
-keep public class * extends android.content.ContentProvider
-keep public class * extends android.app.backup.BackupAgentHelper
-keep public class * extends android.preference.Preference

##--- For:保持自定义控件类不被混淆 ---
-keepclasseswithmembers class * {
    public <init>(android.content.Context, android.util.AttributeSet);
}
-keepclasseswithmembers class * {
    public <init>(android.content.Context, android.util.AttributeSet, int);
}
##--- For:android-support-v4 ---
-dontwarn android.support.v4.**
-keep class android.support.v4.** { *; }
-keep interface android.support.v4.app.** { *; }
-keep class * extends android.support.v4.** { *; }
-keep public class * extends android.support.v4.**
-keep public class * extends android.support.v4.widget
-keep class * extends android.support.v4.app.** {*;}
-keep class * extends android.support.v4.view.** {*;}

##--- For:Serializable ---
-keep class * implements java.io.Serializable {*;}
-keepnames class * implements java.io.Serializable
-keepclassmembers class * implements java.io.Serializable {*;}

##--- For:Gson ---
-keepattributes *Annotation*
-keep class sun.misc.Unsafe { *; }
-keep class com.idea.fifaalarmclock.entity.***
-keep class com.google.gson.stream.** { *; }

##--- For:Remove log ---
-assumenosideeffects class android.util.Log {
    public static boolean isLoggable(java.lang.String, int);
    public static int v(...);
    public static int i(...);
    public static int w(...);
    public static int d(...);
    public static int e(...);
}

##--- For:attributes(未启用) ---
#-keepattributes SourceFile,LineNumberTable # 保持反编译工具能看到代码的行数，以及release包安装后出现异常信息可以知道在哪行代码出现异常，建议不启用
-keepattributes *Annotation* #使用注解
-keepattributes Signature #过滤泛型  出现类型转换错误时，启用这个
#-keepattributes *Exceptions*,EnclosingMethod  #没试过，未知效果