Android signed APK generation : Proguard exception for referenced class / method not found

Question

I need to generate a signed APK for Play Store. ( using Android Studio ) If I do that without proguard ( minifyEnabled false in build.gradle ) all works fine!

If I activate it with default parameters :

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

I receive these warnings

:app:proguardRelease
Warning: com.android.volley.error.VolleyErrorHelper$1: can't find superclass or interface com.google.gson.reflect.TypeToken
Warning: com.android.volley.error.VolleyErrorHelper: can't find referenced class com.google.gson.Gson
Warning: com.android.volley.error.VolleyErrorHelper: can't find referenced class com.google.gson.Gson
Warning: com.android.volley.error.VolleyErrorHelper: can't find referenced method 'java.lang.reflect.Type getType()' in program class com.android.volley.error.VolleyErrorHelper$1
Warning: com.android.volley.error.VolleyErrorHelper: can't find referenced class com.google.gson.Gson
Warning: com.android.volley.error.VolleyErrorHelper$1: can't find referenced class com.google.gson.reflect.TypeToken
Warning: com.android.volley.error.VolleyErrorHelper$1: can't find referenced class com.google.gson.reflect.TypeToken
Warning: com.android.volley.error.VolleyErrorHelper$1: can't find referenced class com.google.gson.reflect.TypeToken
Warning: com.android.volley.request.GsonRequest: can't find referenced class com.google.gson.Gson
Warning: com.android.volley.request.GsonRequest: can't find referenced class com.google.gson.Gson
Warning: com.android.volley.request.GsonRequest: can't find referenced class com.google.gson.Gson
Warning: com.android.volley.request.GsonRequest: can't find referenced class com.google.gson.JsonSyntaxException
Warning: com.android.volley.request.GsonRequest: can't find referenced class com.google.gson.JsonSyntaxException
Warning: com.android.volley.request.GsonRequest: can't find referenced class com.google.gson.Gson
Warning: com.android.volley.request.GsonRequest: can't find referenced class com.google.gson.JsonSyntaxException
Warning: com.squareup.okhttp.internal.huc.HttpsURLConnectionImpl: can't find referenced method 'long getContentLengthLong()' in program class com.squareup.okhttp.internal.huc.HttpURLConnectionImpl
Warning: com.squareup.okhttp.internal.huc.HttpsURLConnectionImpl: can't find referenced method 'long getHeaderFieldLong(java.lang.String,long)' in program class com.squareup.okhttp.internal.huc.HttpURLConnectionImpl
Warning: okio.DeflaterSink: can't find referenced class org.codehaus.mojo.animal_sniffer.IgnoreJRERequirement
Warning: okio.Okio: can't find referenced class java.nio.file.Files
Warning: okio.Okio: can't find referenced class java.nio.file.Files
Warning: okio.Okio: can't find referenced class java.nio.file.Files
Warning: okio.Okio: can't find referenced class java.nio.file.Path
Warning: okio.Okio: can't find referenced class java.nio.file.OpenOption
Warning: okio.Okio: can't find referenced class java.nio.file.Path
Warning: okio.Okio: can't find referenced class java.nio.file.OpenOption
Warning: okio.Okio: can't find referenced class org.codehaus.mojo.animal_sniffer.IgnoreJRERequirement
Warning: okio.Okio: can't find referenced class java.nio.file.Path
Warning: okio.Okio: can't find referenced class java.nio.file.OpenOption
Warning: okio.Okio: can't find referenced class java.nio.file.Path
Warning: okio.Okio: can't find referenced class java.nio.file.OpenOption
Warning: okio.Okio: can't find referenced class org.codehaus.mojo.animal_sniffer.IgnoreJRERequirement
Warning: there were 28 unresolved references to classes or interfaces.
         You may need to add missing library jars or update their versions.
         If your code works fine without the missing classes, you can suppress
         the warnings with '-dontwarn' options.
         (http://proguard.sourceforge.net/manual/troubleshooting.html#unresolvedclass)
Warning: there were 3 unresolved references to program class members.
         Your input classes appear to be inconsistent.
         You may need to recompile the code.
         (http://proguard.sourceforge.net/manual/troubleshooting.html#unresolvedprogramclassmember)
Exception while processing task 
java.io.IOException: Please correct the above warnings first.
    at proguard.Initializer.execute(Initializer.java:473)
    at proguard.ProGuard.initialize(ProGuard.java:233)
    at proguard.ProGuard.execute(ProGuard.java:98)
    at proguard.gradle.ProGuardTask.proguard(ProGuardTask.java:1074)
    at com.android.build.gradle.tasks.AndroidProGuardTask.doMinification(AndroidProGuardTask.java:137)
    at com.android.build.gradle.tasks.AndroidProGuardTask$1.run(AndroidProGuardTask.java:113)
    at com.android.builder.tasks.Job.runTask(Job.java:48)
    at com.android.build.gradle.tasks.SimpleWorkQueue$EmptyThreadContext.runTask(SimpleWorkQueue.java:41)
    at com.android.builder.tasks.WorkQueue.run(WorkQueue.java:227)
    at java.lang.Thread.run(Thread.java:745)
:app:dexRelease UP-TO-DATE
:app:validateExternalOverrideSigning
:app:packageRelease

And the build process stop with this message :

Error:Execution failed for task ':app:packageRelease'.
> Unable to compute hash of ...\app\build\intermediates\classes-proguard\release\classes.jar

After several tentatives I've found a way to remove the warnings with this lines in my "proguard-rules.pro" :

-dontwarn com.android.volley.**
-dontwarn com.squareup.okhttp.**
-dontwarn okio.**

But the build process still goes in error! Anyone have a workaround for this problem?

Thanks! Davide

Answer 1

After several attemps ... here the solution :

First configure the dontwarn as suggested by Raymond ( maybe this is not necessary but i left it ) :

-dontwarn com.google.gson.**
-dontwarn java.nio.file.**
-dontwarn org.codehaus.mojo.animal_sniffer.**
-dontwarn com.squareup.okhttp.internal.huc.**
-dontwarn com.android.volley.error.**

Then configure Proguard to skip my library :

-keep class com.android.volley.error.** { *; }
-keep class com.squareup.okhttp.internal.huc.** { *; }
-keep class okio.** { *; }

Ather that the compilation was ok but on runtime the application crashed. So, to avoid this problem, i've added these lines :

-keep class android.support.design.widget.** { *; }
-keep interface android.support.design.widget.** { *; }
-dontwarn android.support.design.**

based on some info found from this thread :

java.lang.RuntimeException: Could not inflate Behavior subclass

With this settings i'm able to generate a signed APK of my app.

Answer 2

You have to apply dontwarn to the referenced class instead.

For example:

-dontwarn com.google.gson.**
-dontwarn java.nio.file.**