Couldn't resolve JNIfunction: Android ndk

Question

I want to get the list of installed apps in Android by calling Android methods from C++ code. The first method found ( getPackageManager() ), but the getInstalledApplications() method every time is nil. What is wrong here?

JNIEXPORT jobject JNICALL Java_com_example_davidt_ndkexample_TestNdk_getListOfInstalledApps
    (JNIEnv* env, jobject obj, jobject activity){
     jclass contextWrapperClass = env->FindClass("android/content/ContextWrapper");
     jmethodID getPackageManagerId = env->GetMethodID(contextWrapperClass,"getPackageManager","()Landroid/content/pm/PackageManager;");
     if (getPackageManagerId == 0) {
         fprintf(stderr, "packageManager() not found");
     }

     jobject pm = env->CallObjectMethod(activity, getPackageManagerId);

     jclass PackageManagerClass = env->GetObjectClass(pm);
     jmethodID getInstalledApplicationsId = env->GetMethodID(PackageManagerClass,"getInstalledApplications","(I)[Landroid/content/pm/ApplicationInfo;");
     if (getInstalledApplicationsId == 0) {
        fprintf(stderr, "getInstalledApplications() not found");
     }

     return env->CallObjectMethod(pm, getInstalledApplicationsId);
 }

Answer 1

Looks like your signature descriptor is wrong. I've used the javap tool to check it

javap -s -bootclasspath <Your SDK Installation Path>/platforms/android-25/android.jar android.content.pm.PackageManager

and for getInstalledApplications it returns

public abstract java.util.List<android.content.pm.ApplicationInfo> getInstalledApplications(int);
    descriptor: (I)Ljava/util/List;

so, in your case it has to be

jmethodID getInstalledApplicationsId = env->GetMethodID(PackageManagerClass,"getInstalledApplications","(I)Ljava/util/List");