When destroying the QCamera we have crashes inside the DirectShow plugin for the camera (DSCameraControl)

 

In previous versions the code was:

DSCameraControl::DSCameraControl(QObject *parent)
: QCameraControl(parent)
, m_state(QCamera::UnloadedState)
, m_captureMode(QCamera::CaptureStillImage)

{     m_session = qobject_cast<DSCameraSession*>(parent);     connect(m_session, SIGNAL(statusChanged(QCamera::Status)),               this, SIGNAL(statusChanged(QCamera::Status))); }

so the connection was implicitly destroyed when object was also destroyed.

 

In version Qt5.11.1 & Qt5.11.2 this code has changed using a lamda function into:

DSCameraControl::DSCameraControl(QObject *parent)
: QCameraControl(parent)
, m_state(QCamera::UnloadedState)
, m_captureMode(QCamera::CaptureStillImage)
{
     m_session = qobject_cast<DSCameraSession*>(parent);
     connect(m_session, &DSCameraSession::statusChanged,
              [&](QCamera::Status status)

{                        if (status == QCamera::UnloadedStatus)                              m_state = QCamera::UnloadedState;                        emit statusChanged(status);      }

);
     connect(m_session, &DSCameraSession::cameraError,
            this, &DSCameraControl::error);
}

So the lamda function is called even if the object is destroyed, hence the crash.

 

A solution we found working is the modification below:

DSCameraControl::DSCameraControl(QObject *parent)
: QCameraControl(parent)
, m_state(QCamera::UnloadedState)
, m_captureMode(QCamera::CaptureStillImage)
{
     m_session = qobject_cast<DSCameraSession*>(parent);
     connect(m_session, &DSCameraSession::statusChanged, this,
              [&](QCamera::Status status)

{                        if (status == QCamera::UnloadedStatus)                              m_state = QCamera::UnloadedState;                        emit statusChanged(status);      }

);
     connect(m_session, &DSCameraSession::cameraError,
            this, &DSCameraControl::error);
}