Borland Builder 2007 Child VCL controls and the WindowProc method

Question

I have managed to override a controls WindowProc function in order to determine more events than are supported by Builder (i.e. double middle mouse clicks etc..)

The trouble is when I override say a child components WindowProc the parent still gets the event.

In my case I have a panel which has a button parented with it. The button obscures a part of the panel but when clicking the button the parent (panel) gets the event also (haven't tested that the button gets the event also but wanted to to see if anybody had a solution for this firstly).

Is there any way that you can programatically stop the parent receiving the event or a way of determining whether the event is for the child and not the parent.

The problem I will have is that if the user presses the button the panel event and the button event will be triggered.

Please any advice will be gratefully received.

Joe

Code Example: Note that Panel and Button derive from ConfigComponent class which is where the m_kOldComponentWndMethod and ComponentWndProc method live.

Overriding the panel

//---------------------------------------------------------------------------
CConfigComponentPanel::CConfigComponentPanel( TObject* pkParent,
                                              const CConfigComponentDimensions& rkConfigComponentDimensions,
                                              const CConfigComponentPos& rkConfigComponentPos,
                                              const CConfigSelect::SelectCollection& rkSelectCollection,
                                              TColor kBackgroundColour,
                                              TColor kForegroundColour,
                                              const std::string& rstrDisplayText,
                                              const CConfigFontRef& rkConfigFontRef,
                                              const CConfigComponent::ConfigComponentCollection& rkConfigComponentCollection )
:   CConfigComponent( rkConfigComponentDimensions, rkConfigComponentPos, kBackgroundColour, kForegroundColour ),
    m_pkPanel( new TPanel( ( TComponent* )NULL ) ),
    m_kConfigComponentCollection(),
    m_kSelectCollection(),
    m_kConfigFontRef( rkConfigFontRef ),
    m_strDisplayText( rstrDisplayText )
{
    // Set the parent.
    m_pkPanel->Parent = dynamic_cast<TWinControl*>( pkParent );

    if ( rkSelectCollection.size() > 0 )
    {
        // Store the old window proc method before overriding.
        m_kOldComponentWndMethod = m_pkPanel->WindowProc;
        m_pkPanel->WindowProc = ComponentWndProc;
    }

    // Add selects to collection
    AddSelectsToCollection( rkSelectCollection );
    // Add components to collection
    AddConfigComponentsToCollection( rkConfigComponentCollection );
}
//---------------------------------------------------------------------------

Overriding the Button

//---------------------------------------------------------------------------
CConfigComponentButton::CConfigComponentButton( TObject* pkParent,
                                                const CConfigSelect::SelectCollection& rkSelectCollection,
                                                const CConfigComponentDimensions& rkConfigComponentDimensions,
                                                const CConfigComponentPos& rkConfigComponentPos,
                                                TColor kBackgroundColour,
                                                TColor kForegroundColour,
                                                const CConfigButtonBGProperties& rkConfigButtonBGProperties ):
    CConfigComponent( rkConfigComponentDimensions, rkConfigComponentPos, kBackgroundColour, kForegroundColour ),
    m_kConfigButtonBGProperties( rkConfigButtonBGProperties ),
    m_pkButton( new TAdvToolButton( NULL ) ),
    m_kSelectCollection( rkSelectCollection )
{
    m_pkButton->Parent = dynamic_cast<TWinControl*>( pkParent );

    // Store the old window proc method before overriding.
    m_kOldComponentWndMethod = m_pkButton->WindowProc;
    m_pkButton->WindowProc = ComponentWndProc;
}
//---------------------------------------------------------------------------

The Component Wnd Proc Method ( comes in here twice once for panel and once for button )

//---------------------------------------------------------------------------
void __fastcall CConfigComponent::ComponentWndProc( TMessage& rkMessage )const
{
    if ( rkMessage.Msg == WM_MBUTTONDBLCLK )
    {
        (void)Application->MessageBox( "CConfigComponent::ComponentWndProc", "" );
    }
    if ( rkMessage.Msg == WM_LBUTTONDBLCLK )
    {
        (void)Application->MessageBox( "ComponentWndProc::Left Button", "" );
    }

    if ( m_kOldComponentWndMethod )
    {
        m_kOldComponentWndMethod( rkMessage );
    }
}
//---------------------------------------------------------------------------

Thanks, Joe

Aplogies - I have now tried it with the button as well as the panel so in the case where I press the button I get the event for both the panel and the button. Even though the button is obscuring the panel? I guess this is the way that the VCL works and makes a lot of sense but can I switch this off and what are the dangers of doing so? — Yos
What button event(s) exactly are you seeing on the Panel? Please show your actual code. Sounds like your WindowProc is not handling messages correctly. — Remy Lebeau
That may be the case as I mocked up another example where by I used a button and a panel and just used the VCL given events, say OnClick and the same test revealed that the button click got the event instead of both the button (child) and the panel (parent). My code is as follows: — Yos

Remy Lebeau Remy Lebeau · Accepted Answer · 2012-01-13T19:04:05

TAdvToolButton is a TGraphicControl descendant. TGraphicalControl does not have its own window and thus cannot receive user input directly. User input is directed to the Parent window, so the WindowProc of the Parent sees the messages first. If the input occured within the client area of a child TGraphicControl, the Parent then forwards the input to that child. That is why you are seeing user input messages occur in both components. If you change your CConfigComponentButton class to use a windowed button, like TButton or TBitBtn, you will not see the duplicate messages anymore since user input will be directed to the button directly and not to the parent TPanel.

Borland Builder 2007 Child VCL controls and the WindowProc method

1 Answers