从中得到：
如何告诉ProGuard保留私有字段而不指定每个字段

根据 ProGuard文档，通配符匹配任何
字段。

According to ProGuard documenation the wildcard matches any field.

最重要的是，你可以使用否定符（！）。
（ http://proguard.sourceforge.net/#manual/usage.html ）

Top of that, You can use negators (!). (http://proguard.sourceforge.net/#manual/usage.html)

属性名称可以包含？，*和**通配符，它​​们可以是
，前面是
的！否定。

Attribute names can contain ?, *, and ** wildcards, and they can be preceded by the ! negator.

我在这个领域并不是那么有经验，所以这是一个猜测，但更容易在新评论中写。这样的事情应该完成工作（没有测试）：

I am not so experienced in this field, so rather it is a guess, but easier to write in a new comment. Something like this should do the job (NOT TESTED):

-keepclassmembers class * { //should find all classes 
    !private <fields>;    
    <methods>;
    <init>; //and keep every field, method, constructor apart from private fields
}

可能是你可以这样使用，但不确定它是如何与否定器一起工作的：

May be you can use like this, but do not sure how it works with a negator first:

-keepclassmembers class * { //should find all classes 
    !private <fields>;    
    *; //should exclude everything except private fields, which should be obfuscated.
}