dock title bar crash on close

[Alundra]

Hi all,
I have a dock widget custom class who use a custom titlebar.
All works fine but when I close the application and one dock is floating, I have a crash.
Without the custom titlebar I have 0 crash, I tried to find but all looks fine to me.
Code :

CDockWidget::CDockWidget( const QString& Title, QWidget* Parent ) :
QDockWidget( Title, Parent )
{
  m_Titlebar = new CTitlebarWidget( this );
  setTitleBarWidget( m_Titlebar );
  installEventFilter( this );
}
 
bool CDockWidget::eventFilter( QObject* watched, QEvent* event )
{
  switch( event->type() )
  {
    case QEvent::WindowTitleChange :
    {
      m_Titlebar->SetTitle( windowTitle() );
      return true;
    }
 
    case QEvent::NonClientAreaMouseButtonDblClick :
    {
      if( isMaximized() )
        showNormal();
      else
        showMaximized();
      return true;
    }
  }
  return false;
}

CDockWidget::CDockWidget( const QString& Title, QWidget* Parent ) :
QDockWidget( Title, Parent )
{
  m_Titlebar = new CTitlebarWidget( this );
  setTitleBarWidget( m_Titlebar );
  installEventFilter( this );
}

bool CDockWidget::eventFilter( QObject* watched, QEvent* event )
{
  switch( event->type() )
  {
    case QEvent::WindowTitleChange :
    {
      m_Titlebar->SetTitle( windowTitle() );
      return true;
    }

    case QEvent::NonClientAreaMouseButtonDblClick :
    {
      if( isMaximized() )
        showNormal();
      else
        showMaximized();
      return true;
    }
  }
  return false;
}

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CTitlebarWidget::CTitlebarWidget( QWidget* Parent ) :
QFrame( Parent )
{
  // Set the object name.
  setObjectName( "Titlebar" );
 
  // Connect the dock signal when the floating state change.
  connect( Parent, SIGNAL( topLevelChanged( bool ) ), this, SLOT( ChangeFloatingState( bool ) ) );
 
  // Create the title label.
  m_TitleLabel = new QLabel( Parent->windowTitle() );
  m_TitleLabel->setObjectName( "TitlebarLabel" );
 
  // Minimize button.
  m_MinimizeButton = new QToolButton;
  m_MinimizeButton->setObjectName( "TitlebarMinimizeButton" );
  connect( m_MinimizeButton, SIGNAL( clicked() ), this, SLOT( MinimizeButton() ) );
 
  // Maximize button.
  m_MaximizeButton = new QToolButton;
  m_MaximizeButton->setObjectName( "TitlebarMaximizeButton" );
  connect( m_MaximizeButton, SIGNAL( clicked() ), this, SLOT( ChangeParentMaximizeState() ) );
 
  // Float button.
  m_FloatButton = new QToolButton;
  m_FloatButton->setObjectName( "TitlebarFloatButton" );
  connect( m_FloatButton, SIGNAL( clicked() ), this, SLOT( FloatButton() ) );
 
  // Close button.
  m_CloseButton = new QToolButton;
  m_CloseButton->setObjectName( "TitlebarCloseButton" );
  connect( m_CloseButton, SIGNAL( clicked() ), Parent, SLOT( close() ) );
 
  // Create the control layout.
  QHBoxLayout* ControlLayout = new QHBoxLayout;
  ControlLayout->setMargin( 0 );
  ControlLayout->setSpacing( 0 );
  ControlLayout->addWidget( m_MinimizeButton );
  ControlLayout->addWidget( m_MaximizeButton );
  ControlLayout->addWidget( m_FloatButton );
  ControlLayout->addWidget( m_CloseButton );
 
  // Set the floating state.
  CDockWidget* ParentDock = static_cast< CDockWidget* >( Parent );
  ChangeFloatingState( ParentDock->isFloating() );
 
  // Create the layout.
  QHBoxLayout* Layout = new QHBoxLayout;
  Layout->setMargin( 4 );
  Layout->addWidget( m_TitleLabel );
  Layout->addLayout( ControlLayout );
 
  // Set the layout.
  setLayout( Layout );
}
 
void CTitlebarWidget::SetTitle( const QString& Title )
{
  m_TitleLabel->setText( Title );
}
 
QString CTitlebarWidget::GetTitle() const
{
  return m_TitleLabel->text();
}
 
void CTitlebarWidget::mouseDoubleClickEvent( QMouseEvent* event )
{
  ChangeParentMaximizeState();
}
 
void CTitlebarWidget::mouseMoveEvent( QMouseEvent* event )
{
  // Base class.
  QFrame::mouseMoveEvent( event );
 
  // Check if we move with the left button.
  if( event->buttons() == Qt::MouseButton::LeftButton )
  {
    // Cast the parent.
    CDockWidget* Parent = static_cast< CDockWidget* >( parent() );
 
    // Change parent state.
    if( Parent->isMaximized() )
      Parent->showNormal();
  }
}
 
void CTitlebarWidget::MinimizeButton()
{
  CDockWidget* Parent = static_cast< CDockWidget* >( parent() );
  Parent->setFloating( false );
}
 
void CTitlebarWidget::FloatButton()
{
  CDockWidget* Parent = static_cast< CDockWidget* >( parent() );
  Parent->setFloating( true );
}
 
void CTitlebarWidget::ChangeParentMaximizeState()
{
  // Cast the parent.
  CDockWidget* Parent = static_cast< CDockWidget* >( parent() );
 
  // Change parent state.
  if( Parent->isMaximized() )
    Parent->showNormal();
  else
    Parent->showMaximized();
}
 
void CTitlebarWidget::ChangeFloatingState( bool Floating )
{
  if( Floating )
  {
    m_MinimizeButton->setVisible( true );
    m_MaximizeButton->setVisible( true );
    m_FloatButton->setVisible( false );
  }
  else
  {
    m_MinimizeButton->setVisible( false );
    m_MaximizeButton->setVisible( false );
    m_FloatButton->setVisible( true );
  }
}

CTitlebarWidget::CTitlebarWidget( QWidget* Parent ) :
QFrame( Parent )
{
  // Set the object name.
  setObjectName( "Titlebar" );

  // Connect the dock signal when the floating state change.
  connect( Parent, SIGNAL( topLevelChanged( bool ) ), this, SLOT( ChangeFloatingState( bool ) ) );

  // Create the title label.
  m_TitleLabel = new QLabel( Parent->windowTitle() );
  m_TitleLabel->setObjectName( "TitlebarLabel" );

  // Minimize button.
  m_MinimizeButton = new QToolButton;
  m_MinimizeButton->setObjectName( "TitlebarMinimizeButton" );
  connect( m_MinimizeButton, SIGNAL( clicked() ), this, SLOT( MinimizeButton() ) );

  // Maximize button.
  m_MaximizeButton = new QToolButton;
  m_MaximizeButton->setObjectName( "TitlebarMaximizeButton" );
  connect( m_MaximizeButton, SIGNAL( clicked() ), this, SLOT( ChangeParentMaximizeState() ) );

  // Float button.
  m_FloatButton = new QToolButton;
  m_FloatButton->setObjectName( "TitlebarFloatButton" );
  connect( m_FloatButton, SIGNAL( clicked() ), this, SLOT( FloatButton() ) );

  // Close button.
  m_CloseButton = new QToolButton;
  m_CloseButton->setObjectName( "TitlebarCloseButton" );
  connect( m_CloseButton, SIGNAL( clicked() ), Parent, SLOT( close() ) );

  // Create the control layout.
  QHBoxLayout* ControlLayout = new QHBoxLayout;
  ControlLayout->setMargin( 0 );
  ControlLayout->setSpacing( 0 );
  ControlLayout->addWidget( m_MinimizeButton );
  ControlLayout->addWidget( m_MaximizeButton );
  ControlLayout->addWidget( m_FloatButton );
  ControlLayout->addWidget( m_CloseButton );

  // Set the floating state.
  CDockWidget* ParentDock = static_cast< CDockWidget* >( Parent );
  ChangeFloatingState( ParentDock->isFloating() );

  // Create the layout.
  QHBoxLayout* Layout = new QHBoxLayout;
  Layout->setMargin( 4 );
  Layout->addWidget( m_TitleLabel );
  Layout->addLayout( ControlLayout );

  // Set the layout.
  setLayout( Layout );
}

void CTitlebarWidget::SetTitle( const QString& Title )
{
  m_TitleLabel->setText( Title );
}

QString CTitlebarWidget::GetTitle() const
{
  return m_TitleLabel->text();
}

void CTitlebarWidget::mouseDoubleClickEvent( QMouseEvent* event )
{
  ChangeParentMaximizeState();
}

void CTitlebarWidget::mouseMoveEvent( QMouseEvent* event )
{
  // Base class.
  QFrame::mouseMoveEvent( event );

  // Check if we move with the left button.
  if( event->buttons() == Qt::MouseButton::LeftButton )
  {
    // Cast the parent.
    CDockWidget* Parent = static_cast< CDockWidget* >( parent() );

    // Change parent state.
    if( Parent->isMaximized() )
      Parent->showNormal();
  }
}

void CTitlebarWidget::MinimizeButton()
{
  CDockWidget* Parent = static_cast< CDockWidget* >( parent() );
  Parent->setFloating( false );
}

void CTitlebarWidget::FloatButton()
{
  CDockWidget* Parent = static_cast< CDockWidget* >( parent() );
  Parent->setFloating( true );
}

void CTitlebarWidget::ChangeParentMaximizeState()
{
  // Cast the parent.
  CDockWidget* Parent = static_cast< CDockWidget* >( parent() );

  // Change parent state.
  if( Parent->isMaximized() )
    Parent->showNormal();
  else
    Parent->showMaximized();
}

void CTitlebarWidget::ChangeFloatingState( bool Floating )
{
  if( Floating )
  {
    m_MinimizeButton->setVisible( true );
    m_MaximizeButton->setVisible( true );
    m_FloatButton->setVisible( false );
  }
  else
  {
    m_MinimizeButton->setVisible( false );
    m_MaximizeButton->setVisible( false );
    m_FloatButton->setVisible( true );
  }
}

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Is it a possible bug of Qt ?
Thanks

[anda_skoa]

What's the stack trace when you get the crash?
Could m_Titlebar be invalid in the even filter?

Cheers,
_

P.S.: instead of installing an event filter on yourself, how about implementing the event() method?
Should be the same result but much cleaner code wise.

[yuzhouzhiwai]

you can debug your program with the stacktrace .
A probable reason is violence memory access

[Alundra]

What's the stack trace when you get the crash?
P.S.: instead of installing an event filter on yourself, how about implementing the event() method?
Should be the same result but much cleaner code wise.

Thanks for the tip, I changed to :

bool CDockWidget::event( QEvent* event )
{
  switch( event->type() )
  {
    case QEvent::WindowTitleChange :
    {
      m_Titlebar->SetTitle( windowTitle() );
      return true;
    }
 
    case QEvent::NonClientAreaMouseButtonDblClick :
    {
      if( isMaximized() )
        showNormal();
      else
        showMaximized();
      return true;
    }
  }
  return QDockWidget::event( event );
}

bool CDockWidget::event( QEvent* event )
{
  switch( event->type() )
  {
    case QEvent::WindowTitleChange :
    {
      m_Titlebar->SetTitle( windowTitle() );
      return true;
    }

    case QEvent::NonClientAreaMouseButtonDblClick :
    {
      if( isMaximized() )
        showNormal();
      else
        showMaximized();
      return true;
    }
  }
  return QDockWidget::event( event );
}

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I still searching where the crash is from, maybe something missing in the custom QDockWidget.

[Alundra]

I have found the crash, it's here :

void CMainEditorWindow::closeEvent( QCloseEvent* event )
{
  DE::CEngine::Shutdown();
  SDL_Quit();
}

void CMainEditorWindow::closeEvent( QCloseEvent* event )
{
  DE::CEngine::Shutdown();
  SDL_Quit();
}

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Apparently it's because I use a QTimer to refresh my central widget who is a 3D render.
When the application close, manager clear data but the render is called who should not.
Is it a way to avoid this problem ? Maybe a way to know the app is closing ?
Here the code of the widget who call the QTimer :

IRenderWidget::IRenderWidget( QWidget* Parent ) :
QWidget( Parent ),
m_Initialized( false ),
m_RenderWindow( NULL )
{
  // Initialize the widget.
  setMinimumSize( 320, 240 );
  setAttribute( Qt::WA_PaintOnScreen );
  setAttribute( Qt::WA_OpaquePaintEvent );
  setAttribute( Qt::WA_NoSystemBackground );
  setFocusPolicy( Qt::StrongFocus );
  setMouseTracking( true );
 
  // Set the timer interval.
  m_Timer.setInterval( static_cast< int >( (1.0f / 60.0f) * 1000.0f ) );
}

IRenderWidget::IRenderWidget( QWidget* Parent ) :
QWidget( Parent ),
m_Initialized( false ),
m_RenderWindow( NULL )
{
  // Initialize the widget.
  setMinimumSize( 320, 240 );
  setAttribute( Qt::WA_PaintOnScreen );
  setAttribute( Qt::WA_OpaquePaintEvent );
  setAttribute( Qt::WA_NoSystemBackground );
  setFocusPolicy( Qt::StrongFocus );
  setMouseTracking( true );

  // Set the timer interval.
  m_Timer.setInterval( static_cast< int >( (1.0f / 60.0f) * 1000.0f ) );
}

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Thanks

EDIT: I have found a solution, say me if it's the only one possible :

void IRenderWidget::closeEvent( QCloseEvent* event )
{
  disconnect( &m_Timer, SIGNAL( timeout() ), this, SLOT( UpdateOneFrame() ) );
}
 
void CMainEditorWindow::closeEvent( QCloseEvent* event )
{
  centralWidget()->close();
  DE::CEngine::Shutdown();
  SDL_Quit();
}

void IRenderWidget::closeEvent( QCloseEvent* event )
{
  disconnect( &m_Timer, SIGNAL( timeout() ), this, SLOT( UpdateOneFrame() ) );
}

void CMainEditorWindow::closeEvent( QCloseEvent* event )
{
  centralWidget()->close();
  DE::CEngine::Shutdown();
  SDL_Quit();
}

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[d_stranz]

I still searching where the crash is from, maybe something missing in the custom QDockWidget.

Learn how to use a debugger. As others have suggested, the stack trace will tell you exactly where the crash occurs.

Edit -- I see our posts crossed... this is what I originally said:

I would not be surprised to find that it is this line:

CDockWidget* Parent = static_cast< CDockWidget* >( parent() );

CDockWidget* Parent = static_cast< CDockWidget* >( parent() );

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How do you know that parent() returns a CDockWidget? You don't check, you just assume that the static_cast<> returns a pointer to one. QDockWidget might have several layers of widgets between itself and its contents to help with layout (like QFrame, QAbstractScrollArea, and so forth). Better code is:

CDockWidget* pParent = qobject_cast< CDockWidget* >( parent() );
if ( pParent )
{
   // Non-null, so it really is a CDockWidget and it is safe to do something with it
}

CDockWidget* pParent = qobject_cast< CDockWidget* >( parent() );
if ( pParent )
{
   // Non-null, so it really is a CDockWidget and it is safe to do something with it
}

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To answer your other question:

void IRenderWidget::closeEvent( QCloseEvent* event )
{
disconnect( &m_Timer, SIGNAL( timeout() ), this, SLOT( UpdateOneFrame() ) );
}

void IRenderWidget::closeEvent( QCloseEvent* event )
{
disconnect( &m_Timer, SIGNAL( timeout() ), this, SLOT( UpdateOneFrame() ) );
}

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Can't you just call QTimer::stop() instead? "mTimer" looks like it is a member variable in your IRenderWidget class, so it will be disconnected and destroyed when the IRenderWidget instance is destroyed.

[Alundra]

Learn how to use a debugger.

I saw it, but sounded too weird to me, couldn't believe it.

How do you know that parent() returns a CDockWidget?

Because CTitleBarWidget is always on a CDockWidget, it's the custom titlebar widget.

Can't you just call QTimer::stop() instead? "mTimer" looks like it is a member variable in your IRenderWidget class, so it will be disconnected and destroyed when the IRenderWidget instance is destroyed.

The problem is this render widget is central widget and if I don't do that I have the crash, I must stop myself ...
Image to show you how it is : http://uppix.com/f-DreamEditor1453839b9d00168cf5.png.
It's weird that I only had crash when floating, but the leak was always there.