Gson Nested classes are null while using proguard

Question

Warning: class 'com.google.gson.internal.bind.ReflectiveTypeAdapterFactory' is calling Class.getDeclaredFields on class.

After enabling proguard found some issues mentioned below:

1. Nested static classes are null.
2. List of a custom object in a class is null

Already refer the following bugs, but no luck:

Proguard issue while using GSON Using GSON with proguard enabled

Answer 1

I was able to fix this issue by doing three things to my proguard-rules.pro file:

First, makes sure ProGuard doesn't change the names of any of your custom classes you serialize with Gson. Let's say that you have a class called Classname. To exempt it, add this to your progaurd-rules.pro:

-keepclassmembernames class com.your.package.classname { <fields>; }

(Replace com.your.package.classname with your actual package and class name)

I had to do this for like a dozen classes. Don't forget to exempt any member variables of those classes that are also custom. Exempt inner classes with classname$innerclass instead of classname.

Second, add the rules that the Gson library recommends. They can be found here. Here they are as of writing:

##---------------Begin: proguard configuration for Gson  ----------
# Gson uses generic type information stored in a class file when working with fields. Proguard
# removes such information by default, so configure it to keep all of it.
-keepattributes Signature

# For using GSON @Expose annotation
-keepattributes *Annotation*

# Gson specific classes
-dontwarn sun.misc.**
#-keep class com.google.gson.stream.** { *; }

# Application classes that will be serialized/deserialized over Gson
-keep class com.google.gson.examples.android.model.** { <fields>; }

# Prevent proguard from stripping interface information from TypeAdapter, TypeAdapterFactory,
# JsonSerializer, JsonDeserializer instances (so they can be used in @JsonAdapter)
-keep class * extends com.google.gson.TypeAdapter
-keep class * implements com.google.gson.TypeAdapterFactory
-keep class * implements com.google.gson.JsonSerializer
-keep class * implements com.google.gson.JsonDeserializer

# Prevent R8 from leaving Data object members always null
-keepclassmembers,allowobfuscation class * {
  @com.google.gson.annotations.SerializedName <fields>;
}

# Retain generic signatures of TypeToken and its subclasses with R8 version 3.0 and higher.
-keep,allowobfuscation,allowshrinking class com.google.gson.reflect.TypeToken
-keep,allowobfuscation,allowshrinking class * extends com.google.gson.reflect.TypeToken

##---------------End: proguard configuration for Gson  ----------

Last, add in these two rules:

-dontwarn java.lang.reflect.**
-keep class kotlin.** { *; }

These are what fixed the nested null issue I had - Of course, after I had done the above steps.