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Showing content from https://github.com/bytedeco/javacpp/issues/419 below:

Qt virtual QObject · Issue #419 · bytedeco/javacpp · GitHub

Hi,

I'm trying to implement a custom event function in a class extending QApplication.

public native @Cast("bool") boolean eventFilter(QObject watched, QEvent event);

When overriding this function in java, the new implementation is not called.

Also, this function is missing on the java side:

@Virtual protected native void customEvent(QEvent event);

To fix this, I added this function to qt/src/main/java/org/bytedeco/qt/presets/Qt5Core.java:

@Override
protected String[] virtual() {
return new String[]{"QObject"};
}

I'm using mvn install -DskipTests=true -Djavacpp.cppbuild.skip to update the generated files.
This changes will be created in qt/src/gen/java/org/bytedeco/qt/Qt5Core/QObject.java:

-    public native @Cast("bool") boolean event(QEvent event);
-    public native @Cast("bool") boolean eventFilter(QObject watched, QEvent event);
+    @Virtual public native @Cast("bool") boolean event(QEvent event);
+    @Virtual public native @Cast("bool") boolean eventFilter(QObject watched, QEvent event);

+    @Virtual protected native void timerEvent(QTimerEvent event);
+    @Virtual protected native void childEvent(QChildEvent event);
+    @Virtual protected native void customEvent(QEvent event);

But compiling fails:

/(...)/javacpp-presets/qt/target/native/org/bytedeco/qt/linux-x86_64/jniQt5Core.cpp: In function 'jboolean Java_org_bytedeco_qt_Qt5Core_QCoreApplication_event(JNIEnv*, jobject, jobject)':
/(...)/javacpp-presets/qt/target/native/org/bytedeco/qt/linux-x86_64/jniQt5Core.cpp:9555:152: error: 'virtual bool QCoreApplication::event(QEvent*)' is protected within this context
 9555 |         bool rval = (bool)(dynamic_cast<JavaCPP_QCoreApplication*>(ptr) != NULL ? ((JavaCPP_QCoreApplication*)ptr)->super_event(ptr0) : ptr->event(ptr0));
      |                                                                                                                                                        ^
In file included from /(...)/javacpp-presets/qt/target/native/org/bytedeco/qt/linux-x86_64/jniQt5Core.cpp:103:
/(...)/javacpp-presets/qt/cppbuild/linux-x86_64/include/QtCore/qcoreapplication.h:190:10: note: declared protected here
  190 |     bool event(QEvent *) override;
      |          ^~~~~

qobject.h:

public:
  virtual bool event(QEvent *event);

qcoreapplication.h:

protected:
    bool event(QEvent *) override;

Because it is protected in QCoreApplication, it can not be called here (jniQt5Core.cpp):

JNIEXPORT jboolean JNICALL Java_org_bytedeco_qt_Qt5Core_QCoreApplication_event(JNIEnv* env, jobject obj, jobject arg0) {
    QCoreApplication* ptr = (QCoreApplication*)jlong_to_ptr(env->GetLongField(obj, JavaCPP_addressFID));
    if (ptr == NULL) {
        env->ThrowNew(JavaCPP_getClass(env, 6), "This pointer address is NULL.");
        return 0;
    }
    jlong position = env->GetLongField(obj, JavaCPP_positionFID);
    ptr += position;
    QEvent* ptr0 = arg0 == NULL ? NULL : (QEvent*)jlong_to_ptr(env->GetLongField(arg0, JavaCPP_addressFID));
    jlong position0 = arg0 == NULL ? 0 : env->GetLongField(arg0, JavaCPP_positionFID);
    ptr0 += position0;
    jboolean rarg = 0;
    jthrowable exc = NULL;
    try {
        bool rval = (bool)(dynamic_cast<JavaCPP_QCoreApplication*>(ptr) != NULL ? ((JavaCPP_QCoreApplication*)ptr)->super_event(ptr0) : ptr->event(ptr0));
        rarg = (jboolean)rval;
    } catch (...) {
        exc = JavaCPP_handleException(env, 9);
    }

    if (exc != NULL) {
        env->Throw(exc);
    }
    return rarg;
}

In this line: bool rval = (bool)(dynamic_cast<JavaCPP_QCoreApplication*>(ptr) != NULL ? ((JavaCPP_QCoreApplication*)ptr)->super_event(ptr0) : ptr->event(ptr0));,
when ptr is of type QCoreApplication, ptr->event is not valid, because it is protected.

I tried this changes:
In file org.bytedeco.qt.presets.Qt5Core, in function public void map(InfoMap infoMap) I added

.put(new Info("QObject::event").javaNames("someExampleName"))

this will rename the function as expected. But changing it to:

.put(new Info("QCoreApplication::event").javaNames("someExampleName"))

nothing will be changed. Also

.put(new Info("QCoreApplication::event").skip())

and adding "QCoreApplication::event" to protected String[] skip() is not possible.

Maybe changing ptr->event(ptr0) to ((QObject*)ptr)->event(ptr0) will work?

Is there a way to fix this?

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