Question

I’m trying to combine some existing Qt code written in C++ with some code written in Java using Qt Jambi, but I’m not quite sure how to do it. I’m basically trying to acieve two things:

1. Pass a QObject from C++ to Java using JNI
2. Pass a Qt Jambi QObject from Java to C++

It looks like I can pass the pointer directly and then wrap it in QNativePointer on the Java side, but I can’t figure out how to turn a QNativePointer back into the original object, wrapped by Qt Jambi.

Eg: I can pass a QWidget* as a long to Java and then create a QNativePointer in Java, but how can I then construct a QWidget out of this? QJambiObject and QObject dont seem to have a “setNativePointer” method and I’m not sure how to convert it.

In C++:

QWidget* widget = ...
jclass cls = env->FindClass("Test");
jmethodID mid = env->GetStaticMethodID(cls, "test", "(I)V");
env->CallStaticVoidMethod(cls, mid, int(widget));

In Java:

public class Test {
    public static void test (int ptr) {
        QNativePointer pointer = new QNativePointer(QNativePointer.Type.Int);
        pointer.setIntValue(ptr);

        QWidget widget = ...

Thanks!

Answer 1

For other people looking at this, check this out:
http://labs.trolltech.com/blogs/2007/08/24/extremely-interesting-jambi-trick-x-instantiating-java-widgets-from-c/

Especially this part:

The qtjambi_from_QWidget() call will
either create a new Java widget if the
parent widget was created in C++, or
it will return the existing Java
object if the parent was created in
Java. If it has to create a new java
object, the type of this will be the
closest Java supertype known to Qt
Jambi. If you have mapped your own C++
widgets and want to use them correctly
in calls such as these, you have to
make sure the initialization code of
your generated library is called prior
to the conversion takes place. Also
note that in qtjambi_core.h you will
find several other convenient
conversion functions that can be used
to convert back and forth between C++
and JNI, as well as other convenient,
JNI-based code.