How to get application context for JNI library

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1

I am trying to use a Android Java library with Unreal JNI. Problem is that the library requires an Android application context, and I have not been able to find out how to get it in Unreal.

The GameActivitivity.java naturally has an context available, but passing that through c++ code to a library seems to either mangle the context reference so that it becomes invalid object or weak ref, or the method is not found due to false signature, I think.

Here is one trial

// Get UE4 GameActivity class 
jclass game_activity_class = FAndroidApplication::FindJavaClass("com.epicgames.ue4.GameActivity");

// Use a method inserted in UPL.xml to get the context
jmethodID getActivity = env->GetMethodID(game_activity_class, "AndroidThunkJava_GetApplicationContext", "()Ljava/lang/Object;");
jobject main_ctx = env->CallObjectMethod(game_activity_class, getActivity);

// convert to global ref
globalGameCtx = reinterpret_cast<jobject>(env->NewGlobalRef(main_ctx));

// get the library class
jclass localRef = FAndroidApplication::FindJavaClass("com/comp/prod/lib/MyLibManager");

// get the initialize(...) method from the target library
jmethodID initialize_method = env->GetStaticMethodID(localRef, "initialize", "(Landroid/content/Context;Ljava/lang/String;Ljava/lang/String;)V");

// call the initialize(...) method in the target library
env->CallStaticVoidMethod(localRef, initialize_method, globalGameCtx, "TEST", "TEST");

This results into runtime error

     : signal 6 (SIGABRT), code -6 (SI_TKILL), fault addr --------

     : Abort message: 'java_vm_ext.cc:534] JNI DETECTED ERROR IN APPLICATION: can't call java.lang.Object com.epicgames.ue4.GameActivity.AndroidThunkJava_GetApplicationContext() on instance of java.lang.Class<com.epicgames.ue4.GameActivity>'

Any ideas how to fix? Or a better way to obtain context?

2

FAndroidApplication::GetGameActivityThis() ?

3

I ended up solving this by calling java lib directly from UPL file, where you can get the context simply by

Get().getApplicationContext()

4

Thanks for the answer. This may work as well, but can not verify it anymore.