Return QObject undefined

[coderbob]

If I pass an object to a QML and that object in turn grabs another object I error out with the following:

"code example/main.js:4: TypeError: Result of expression 'failedObject' [undefined] is not an object."

Now if I change line 16 in object1.h (and of course its matching function in object1.cpp) to QObject the script will convert it fine and I will not have any errors. The problem with this is I then have to qobject_cast when using the function internally in the c++ code. This casting internally just to get it to be recognized correctly in the script feels wrong to me.

Since my class inherits QObject I was under the impression I should not have to use qRegisterMetaType. It appears to be registered correctly since it knows how to cast it in the script when it is passed as a QObject.

I am confused on why I must use QObject and let the script auto cast it and I cannot reference my class directly if it is already registered. Also not sure if casting my class internally will have a performance hit or is just bad form?

Short Question: Why cant I reference a return object using my specific class identifier in a script?

I attached a very small code example that will show specifically what the problem is.

[wysota]

My impression is you need to call qmlRegisterType for qml to be aware of your object type.

[coderbob]

That will work for QML code but I am trying to get the script code to reconize it. I need something like qScriptRegisterMetaType but I do not have a QScriptEngine since the script is being handled by the QML.

My guess is it might not be possible right now or I am looking at it wrong.

[wysota]

Could you prepare an example that actually does something? When I run your code I only get a blank window and no messages to the console.

[coderbob]

Could you prepare an example that actually does something?

Just click anywhere in the box and you will see the error message in the console.

Now if I change line 16 in object1.h (and of course its matching function in object1.cpp) to QObject the script will convert it fine and I will not have any errors. The problem with this is I then have to qobject_cast when using the function internally in the c++ code. This casting internally just to get it to be recognized correctly in the script feels wrong to me.

[wysota]

It works (no error, object name is printed) if I use qmlRegisterType. Why haven't you tried it after I have given this solution to you?

[coderbob]

I still get the error, can you please post your code changes.

[wysota]

I added this to main().

qmlRegisterType<Object2>("com.test.object", 1, 0, "Object2");

qmlRegisterType<Object2>("com.test.object", 1, 0, "Object2");

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[coderbob]

I error with:

In file included from object1.h:6,
from main.cpp:7:
object2.h:21: error: explicit specialization in non-namespace scope ‘class Object2’
object2.h:21: error: ‘struct QMetaTypeId<Object2*>’ redeclared with different access
object2.h:21: error: explicit specialization in non-namespace scope ‘class Object2’
object2.h:21: error: ‘struct QMetaTypeId<QDeclarativeListProperty<Object2> >’ redeclared with different access
make: *** [main.o] Error 1

[wysota]

I don't know what you did exactly to get this error but the line I gave you is the only change I made to the whole program (apart including headers for your classes, of course).

#include "object1.h"
#include "object2.h"
 
int main(int argc, char *argv[])
{
  QApplication app(argc, argv);
 
  QDeclarativeView view;
  qmlRegisterType<Object2>("com.test.object", 1, 0, "Object2");
   view.setResizeMode(QDeclarativeView::SizeRootObjectToView); 
 
   Object1 *object1 = new Object1();
 
   view.rootContext()->setContextProperty("myObject1",object1);
 
   view.setSource(QUrl::fromLocalFile("main.qml"));
   view.show();
 
  return app.exec();
}

#include "object1.h"
#include "object2.h"

int main(int argc, char *argv[])
{
  QApplication app(argc, argv);

  QDeclarativeView view;
  qmlRegisterType<Object2>("com.test.object", 1, 0, "Object2");
   view.setResizeMode(QDeclarativeView::SizeRootObjectToView); 

   Object1 *object1 = new Object1();

   view.rootContext()->setContextProperty("myObject1",object1);

   view.setSource(QUrl::fromLocalFile("main.qml"));
   view.show();

  return app.exec();
}

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[coderbob]

Thank you Wysota, the problem I was having was experimenting with other possibilities and I did not back that code out before attempting the qmlRegisterType.

I have noticed that QML behaves differently when these objects are passed to the script as a signal. I have added to the previous code example that reproduces this.

The update adds a singleShot QTimer that passed the object1 twice to the script. Once declared class and the second as a QObject.

When passed as a class it is casted as a QVariant and I will not have access to any properties or slots.

When passed as a QObject I will have access to properties but is also casted differently then when it is passed using the doSomething() function. (Clickign anywhere in the window)

I could not find anyway to cast it from a QVariant in the script so I could access it properly. Also a little confused why it is casting the same object type differently.