Qt on Android, QAndroidJniObject::callStaticMethod problem

[luca]

Hi all,
I'm doing some tests on android using Qt.

The first test is a simple Qt App for Android where I have the following code:

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
        jint a = 2;
        jint b = 4;
        jint max = QAndroidJniObject::callStaticMethod<jint>("java/lang/Math", "max", "(II)I", a, b);
        qDebug() << "********** max " << max;
...
...

and I get the right output.

Now I'm trying to use a simple custom Qt library "testjni.so" from an Android Studio project.
The library is created with QtCreator and has the following code:

static void test1(JNIEnv *env, jobject obj, jint n)
{
    qDebug() << "****************** test1 " << n;
}
static int square(JNIEnv */*env*/, jobject /*obj*/, jint n)
{
    qDebug() << "****************** square " << n;
    return Testjni::square(n);
}
static JNINativeMethod methods[] = {
    { "test1", 
        "(I)V", 
        (void *)test1 },
    { "square",
        "(I)I", 
        (void *)square }
};
JNIEXPORT jint JNI_OnLoad(JavaVM* vm, void* /*reserved*/)
{
    qDebug() << "****************** JNI_OnLoad *************************";
jint a = 2;
        jint b = 4;
        jint max = QAndroidJniObject::callStaticMethod<jint>("java/lang/Math", "max", "(II)I", a, b);
        qDebug() << "********** max " << max;

    JNIEnv* env;
    if (vm->GetEnv(reinterpret_cast<void**>(&env), JNI_VERSION_1_6)
           != JNI_OK) {
        return JNI_ERR;
    }
    jclass javaClass = env->FindClass("com/my/package/testjniandroid/MyJavaNatives");
    if (!javaClass) {
        return JNI_ERR;
    }
    if (env->RegisterNatives(javaClass, methods,
                            sizeof(methods) / sizeof(methods[0])) < 0) {
        return JNI_ERR;
    }
    return JNI_VERSION_1_6;
}

Testjni::Testjni()
{

}

int Testjni::square(int val)
{
    qDebug() << "****************** Testjni::square " << val;
    return val*val;
}

and the Android part is:

protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        System.loadLibrary("testjni");
    }

Now when I start the Android application it load the native library and call JNI_OnLoad but when it execute QAndroidJniObject::callStaticMethod it crash without useful messages.

Where do I wrong?

Thanks

Luca

[benlau]

I am not an expert in JNI. But I have written an Android unit test program to execute Qt code. Java code send message to C++ code via JNI and vice versa. It is working fine.

My code:
quickandroid/ExampleActivityTest.java at DEV · benlau/quickandroid

However, I use ActivityInstrumentationTestCase2 which depend on an existing .apk. C++ code is launched by QtActivity.java instead of calling System.loadLibrary manually. May be the QtActivity has setup something for getting JNI to load Java class correctly?

[luca]

@benlau
Thanks,
it probably depend on QtActivity that set something as you said but can't find the solution...