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Remy Lebeau (TeamB)
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 Posted: Sat Aug 30, 2003 11:43 pm Post subject: Re: OnVisibleChange event |
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"JD" <nospam (AT) nospam (DOT) com> wrote
| Quote: | Can I subclass a TPanel to add an event for when
the Visible property changes? If so, could you also
please provide a sample?
|
When the Visible property is changed, it sends a CM_VISIBLECHANGED message
back to the component. You can subclass the WindowProc property in order to
intercept that message:
TWndMethod OldWndProc;
__fastcall TForm1::TForm1(TComponent *Owner)
: TForm(Owner)
{
OldWndProc = Panel1->WindowProc;
Panel1->WindowProc = PanelWndProc;
}
void __fastvall TForm1::PanelWndProc(TMessage &Message)
{
if( Message.Msg == CM_VISIBLECHANGED )
// do something
OldWndProc(Message);
}
The alternative is to derive a new component from TPanel and override the
inherited VisibleChanging() method instead:
class TMyPanel : public TPanel
{
protected:
DYNAMIC void __fastcall VisibleChanging();
public:
__fastcall TMyPanel(TComponent *Owner);
};
__fastcall TMyPanel::TMyPanel(TComponent *Owner)
: TPanel(Owner)
{
}
void __fastcall TMyPanel::VisibleChanging()
{
// do something
TPanel::VisibleChanging();
}
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