您需要指定要使用正确的符号，以保持内部类。
在ProGuard的说法，这意味着 -keep类my.outer.Class $ MyInnerClass 。这里的关键是使用美元符号（ $ ）的内部和外部类之间的分隔符。

You need to specify that you want to keep the inner class using the proper notation. In the proguard parlance, that means -keep class my.outer.Class$MyInnerClass. The key here is using the dollar-sign ($) as the separator between inner and outer class.

要做到这一点，你还必须指定 -keepattributes InnerClasses ，以便名称 MyInnerClass 不得到模糊处理。这两个设置在一起应该让你的内部类可保持不变。

To do this, you also have to specify -keepattributes InnerClasses, so that the name MyInnerClass doesn't get obfuscated. These two settings together should allow your inner classes to be kept intact.