dumping ground for some jni functions i write

jni_stuff.cpp

#include "native_helper.hpp"
#include <android_native_app_glue.h>
#include <android/log.h>
#include <string>

namespace {

struct JniHelper
{
    JniHelper(struct android_app* app)
    {
        vm = app->activity->vm;
        if (vm->GetEnv((void**)&env, JNI_VERSION_1_6))
        {
            if (!vm->AttachCurrentThread(&env, NULL))
            {
                __android_log_print(ANDROID_LOG_INFO, "JNI-TEST", "attaching thread\n");
                thread_attached = true;
            }
        }
    }

    ~JniHelper()
    {
        if (thread_attached && vm)
        {
            vm->DetachCurrentThread();
            __android_log_print(ANDROID_LOG_INFO, "JNI-TEST", "detaching thread\n");
        }
    }

    JNIEnv* env{};
    JavaVM* vm{};
    bool thread_attached{};
};

int getApiLevel(const struct android_app* app)
{
    return app->activity->sdkVersion;
}

} // namespace

// https://developer.android.com/reference/android/content/Context#getPackageName()
jstring Android_getPackageName(struct android_app* app)
{
    JniHelper jni{app};
    const auto ActivityClass = jni.env->GetObjectClass(app->activity->clazz);
    const auto getPackageName = jni.env->GetMethodID(ActivityClass, "getPackageName", "()Ljava/lang/String;");
    const auto package_name = (jstring)jni.env->CallObjectMethod(app->activity->clazz, getPackageName);
    return package_name;
}

// https://developer.android.com/reference/android/os/Environment#isExternalStorageEmulated()
bool Android_isExternalStorageEmulated(struct android_app* app)
{
    if (getApiLevel(app) < 11)
    {
        return false;
    }

    JniHelper jni{app};

    auto Environment = jni.env->FindClass("android/os/Environment");
    auto isExternalStorageEmulated = jni.env->GetStaticMethodID(Environment, "isExternalStorageEmulated",  "()Z");
    const auto result = jni.env->CallStaticBooleanMethod(Environment, isExternalStorageEmulated);

    return result > 0;
}

// https://developer.android.com/reference/android/os/Environment#isExternalStorageLegacy()
bool Android_isExternalStorageLegacy(struct android_app* app)
{
    if (getApiLevel(app) < 29)
    {
        return false;
    }

    JniHelper jni{app};

    auto Environment = jni.env->FindClass("android/os/Environment");
    auto isExternalStorageLegacy = jni.env->GetStaticMethodID(Environment, "isExternalStorageLegacy",  "()Z");
    const auto result = jni.env->CallStaticBooleanMethod(Environment, isExternalStorageLegacy);

    return result > 0;
}

// https://developer.android.com/reference/android/os/Environment#isExternalStorageManager()
bool Android_isExternalStorageManager(struct android_app* app)
{
    if (getApiLevel(app) < 30)
    {
        return false;
    }

    JniHelper jni{app};

    auto Environment = jni.env->FindClass("android/os/Environment");
    auto isExternalStorageManager = jni.env->GetStaticMethodID(Environment, "isExternalStorageManager",  "()Z");
    const auto result = jni.env->CallStaticBooleanMethod(Environment, isExternalStorageManager);

    return result > 0;
}

// https://developer.android.com/reference/android/os/Environment#isExternalStorageRemovable()
bool Android_isExternalStorageRemovable(struct android_app* app)
{
    if (getApiLevel(app) < 9)
    {
        return false;
    }

    JniHelper jni{app};

    auto Environment = jni.env->FindClass("android/os/Environment");
    auto isExternalStorageRemovable = jni.env->GetStaticMethodID(Environment, "isExternalStorageRemovable",  "()Z");
    const auto result = jni.env->CallStaticBooleanMethod(Environment, isExternalStorageRemovable);

    return result > 0;
}

// https://developer.android.com/reference/android/provider/Settings#ACTION_MANAGE_APP_ALL_FILES_ACCESS_PERMISSION
// https://developer.android.com/reference/android/provider/Settings#ACTION_MANAGE_ALL_FILES_ACCESS_PERMISSION
void Android_requestAppAllFilesFilesPermission(struct android_app* app)
{
    if (getApiLevel(app) < 30)
    {
        return;
    }

    JniHelper jni{app};

    // get all the needed classes
    const auto SettingsClass = jni.env->FindClass("android/provider/Settings");
    const auto ActivityClass = jni.env->FindClass("android/app/Activity");
    const auto UriClass = jni.env->FindClass("android/net/Uri");
    const auto IntentClass = jni.env->FindClass("android/content/Intent");

    // get static string
    const auto ACTION_MANAGE_APP_ALL_FILES_ACCESS_PERMISSION_id = jni.env->GetStaticFieldID(SettingsClass, "ACTION_MANAGE_APP_ALL_FILES_ACCESS_PERMISSION", "Ljava/lang/String;");
    const auto ACTION_MANAGE_APP_ALL_FILES_ACCESS_PERMISSION = (jstring)jni.env->GetStaticObjectField(SettingsClass, ACTION_MANAGE_APP_ALL_FILES_ACCESS_PERMISSION_id);

    // create uri using the package name
    const auto PackageName = Android_getPackageName(app);
    const auto PackageNameUTF = jni.env->GetStringUTFChars(PackageName, NULL);
    const std::string PackageNameUri = std::string{"package:"} + PackageNameUTF;
    jni.env->ReleaseStringUTFChars(PackageName, PackageNameUTF);

    // parse and create uri
    const auto parse = jni.env->GetStaticMethodID(UriClass, "parse", "(Ljava/lang/String;)Landroid/net/Uri;");
    const auto PackageUri = jni.env->CallStaticObjectMethod(UriClass, parse, jni.env->NewStringUTF(PackageNameUri.c_str()));

    // find constructor and create instance of Intent
    const auto IntentClassConstructor = jni.env->GetMethodID(IntentClass, "<init>", "(Ljava/lang/String;Landroid/net/Uri;)V");
    const auto IntentObj = jni.env->NewObject(IntentClass, IntentClassConstructor, ACTION_MANAGE_APP_ALL_FILES_ACCESS_PERMISSION, PackageUri);

    // find and call startActivity()
    const auto startActivity = jni.env->GetMethodID(ActivityClass, "startActivity", "(Landroid/content/Intent;)V");
    jni.env->CallVoidMethod(app->activity->clazz, startActivity, IntentObj);
}

// https://developer.android.com/reference/android/content/Intent#ACTION_GET_CONTENT
// https://developer.android.com/reference/android/content/Intent#ACTION_OPEN_DOCUMENT
void Android_file_picker(struct android_app* app)
{
    JniHelper jni{app};

    // get all the needed classes
    const auto ActivityClass = jni.env->FindClass("android/app/Activity");
    const auto IntentClass = jni.env->FindClass("android/content/Intent");

    // get some constants
    const char* action = getApiLevel(app) < 19 ? "ACTION_GET_CONTENT" : "ACTION_OPEN_DOCUMENT";
    const auto ACTION_XXX_id = jni.env->GetStaticFieldID(IntentClass, action, "Ljava/lang/String;");
    const auto CATEGORY_OPENABLE_id = jni.env->GetStaticFieldID(IntentClass, "CATEGORY_OPENABLE", "Ljava/lang/String;");
    const auto ACTION_XXX = (jstring)jni.env->GetStaticObjectField(IntentClass, ACTION_XXX_id);
    const auto CATEGORY_OPENABLE = (jstring)jni.env->GetStaticObjectField(IntentClass, CATEGORY_OPENABLE_id);

    // find constructor and create instance of Intent
    const auto IntentClassConstructor = jni.env->GetMethodID(IntentClass, "<init>", "(Ljava/lang/String;)V");
    const auto IntentObj = jni.env->NewObject(IntentClass, IntentClassConstructor, ACTION_XXX);

    // need to set a couple of methods
    const auto addCategory = jni.env->GetMethodID(IntentClass, "addCategory", "(Ljava/lang/String;)Landroid/content/Intent;");
    const auto setType = jni.env->GetMethodID(IntentClass, "setType", "(Ljava/lang/String;)Landroid/content/Intent;");

    // these return itself so you can chain methods together
    jni.env->CallObjectMethod(IntentObj, addCategory, CATEGORY_OPENABLE);
    jni.env->CallObjectMethod(IntentObj, setType, jni.env->NewStringUTF("*/*"));

    // find and call startActivity() (todo: handle result somehow)
    const auto startActivityForResult = jni.env->GetMethodID(ActivityClass, "startActivityForResult", "(Landroid/content/Intent;I)V");
    jni.env->CallVoidMethod(app->activity->clazz, startActivityForResult, IntentObj, 0);
}