QObject::connect error / Make sure '...' is registered using qRegisterMetaType()

makopo

Hey there,

for now I'am not really experienced in developing with Qt.
I develop a little program that captures video from an external device. When I start the the program, it is running, but when I press the start button which should start the capture VS prints the following message to the console:

QObject::connect: Cannot queue arguments of type 'CComPtr<IDeckLinkVideoFrame>'
(Make sure 'CComPtr<IDeckLinkVideoFrame>' is registered using qRegisterMetaType().)

I read about qRegisterMetaType() and try to implement it in the constructor of both classes, like this:

qRegisterMetaType<IDeckLinkVideoFrame*>("IDeckLinkVideoFrame*");

I also create a register function in an initializing class and call the function in the constructors too. I still get the error message.

In the programm I use connect for the frame transfer:

QObject::connect(m_emitFrame, &VideoScreenHelper::FrameChanged, this, &VideoScreen::HandleFrame, Qt::AutoConnection);

FrameChanged is emitted in a function that is supported from the DeckLink API. This function should draw the video to the screen.

/**
* The method is called on every incoming frame and is derived from the IDeckLinkScreenPreviewCallback
*/
HRESULT VideoScreenHelper::DrawFrame(IDeckLinkVideoFrame* theFrame) {

	emit FrameChanged(CComPtr<IDeckLinkVideoFrame> (theFrame));
	return S_OK;
}

HandleFrame() manages the setup of the frame.

void VideoScreen::HandleFrame(CComPtr<IDeckLinkVideoFrame> theFrame) {
	if (m_previewHelper != nullptr) {
		m_previewHelper->SetFrame(theFrame);
	}
}

Can someone of you tell me what is going wrong here? It is still confusing...

Christian Ehrlicher

@makopo said in QObject::connect error / Make sure '...' is registered using qRegisterMetaType():

CComPtr<IDeckLinkVideoFrame>
Make sure 'CComPtr<IDeckLinkVideoFrame>' is registered using qRegisterMetaType().

qRegisterMetaType<IDeckLinkVideoFrame*>("IDeckLinkVideoFrame*");

This is not what the error message told you.

Pl45m4

@makopo

As @Christian-Ehrlicher said above, you need to register the complete type (in your case CComPtr<IDeckLinkVideoFrame>).