TCustomHeaderControl.Canvas Property

Provides runtime access to the header control's drawing surface.

Pascal

property Canvas: TCanvas;

C++

__property TCanvas Canvas;

Description

The read-only Canvas property provides access to the header control's drawing surface that can be used when implementing a handler for the OnDrawSection event.

C++ Examples:

Copy Code

/*
Add a THeaderControl to the form and call 
HeaderControl1DrawSection for the OnDrawSection event.
*/
void __fastcall TForm1::HeaderControl1DrawSection(THeaderControl *HeaderControl,
      THeaderSection *Section, const TRect &Rect, bool Pressed)
{
  if (Pressed)
    HeaderControl->Canvas->Font->Color = clRed;
  else
    HeaderControl->Canvas->Font->Color = clBlue;
  HeaderControl->Canvas->TextOut(Rect.Left + HeaderControl->Canvas->Font->Size, Rect.Top + 2, "Custom " + IntToStr(Section->Index));
}

void __fastcall TForm1::FormCreate(TObject *Sender)
{
  THeaderSection *Section;
  for (int i = 0; i <= 4; i++)
  {
    Section = HeaderControl1->Sections->Add();
    Section->Text = "Section " + IntToStr(i);
    Section->MinWidth =
      (Section->Text).Length() *
      HeaderControl1->Font->Size;
    // Owner draw every other section
    if (i % 2 == 0)
      Section->Style = hsOwnerDraw;
    else
      Section->Style = hsText;
  }
}

Delphi Examples:

Copy Code

{
Add a THeaderControl to the form and call 
HeaderControl1DrawSection for the OnDrawSection event.
}
procedure TForm1.FormCreate(Sender: TObject);
var
  HeaderSection: THeaderSection;
  I: Integer;
begin
  for I := 0 to 4 do
  begin
    HeaderSection := HeaderControl1.Sections.Add;
    HeaderSection.Text := 'Text Section ' + IntToStr(I);
    HeaderSection.MinWidth := length(HeaderSection.Text) * Font.Size;
    // Owner draw every other section
    if (I mod 2 = 0) then
      HeaderSection.Style := hsOwnerDraw
    else
      HeaderSection.Style := hsText;
  end;
end;

procedure TForm1.HeaderControl1DrawSection(HeaderControl: THeaderControl;
  Section: THeaderSection; const Rect: TRect; Pressed: Boolean);
begin
  with HeaderControl.Canvas do
  begin
    // highlight pressed sections
    if Pressed then
      Font.Color := clRed
    else
      Font.Color := clBlue;
    TextOut(Rect.Left + Font.Size, Rect.Top + 2, 'Owner Drawn text');
  end;
end;