TDBListBox.OnDrawItem Event

Occurs when an item in an owner-draw list box needs to be redisplayed.

Pascal

property OnDrawItem: TDrawItemEvent;

C++

__property TDrawItemEvent OnDrawItem;

Description

Use OnDrawItem to write a handler for drawing of the items in list boxes with the Style values lbOwnerDrawFixed, lbOwnerDrawVariable, or lbVirtualOwnerDraw. OnDrawItem occurs when the list box needs to display an item. OnDrawItem occurs only for owner-draw list boxes.

The size of the rectangle that contains the item is determined either by the ItemHeight property for fixed owner-draw list boxes or by the response to the OnMeasureItem event for variable owner-draw list boxes.

C++ Examples:

Copy Code

/*
Here is a typical handler for an OnDrawItem event. In the
example, a list box with the lbOwnerDrawFixed style draws a
bitmap to the left of each string.
Select the TListBox and set the ItemHeight property to 32.
Select the ImageList and set the Layout Height and Width to
32.  Double click on the ImageList to load the images.  Be
sure to load in the correct order, logo2, Sunflower,
butterfly.
*/
#include <memory>       //for STL auto_ptr class

Graphics::TBitmap *bitmap0, *bitmap1, *bitmap2;

void __fastcall TForm1::FormCreate(TObject *Sender)
{
  static std::auto_ptr<Graphics::TBitmap> _bitmap0Cleaner(bitmap0 = new Graphics::TBitmap);
  static std::auto_ptr<Graphics::TBitmap> _bitmap1Cleaner(bitmap1 = new Graphics::TBitmap);
  static std::auto_ptr<Graphics::TBitmap> _bitmap2Cleaner(bitmap2 = new Graphics::TBitmap);

  ImageList1->GetBitmap(0, bitmap0);
  ListBox1->Items->AddObject("Flowers", bitmap0);
  ImageList1->GetBitmap(1, bitmap1);
  ListBox1->Items->AddObject("Animal", bitmap1);
  ImageList1->GetBitmap(2, bitmap2);
  ListBox1->Items->AddObject("Butterfly", bitmap2);
}

void __fastcall TForm1::ListBox1DrawItem(TWinControl *Control, int Index,
      TRect &Rect, TOwnerDrawState State)
{
  Graphics::TBitmap *pBitmap; // temporary variable for item’s bitmap
  int     Offset = 2;   // default text offset width
  // note that we draw on the listbox’s canvas, not on the form
  TCanvas *pCanvas = (dynamic_cast<TListBox *>(Control))->Canvas;
  pCanvas->FillRect(Rect); // clear the rectangle
  pBitmap = dynamic_cast<Graphics::TBitmap *>((dynamic_cast<TListBox *>(Control))->Items->Objects[Index]);
  if (pBitmap)
  {
    pCanvas->BrushCopy(
      Bounds(Rect.Left + Offset, Rect.Top, pBitmap->Width, pBitmap->Height),
      pBitmap,
      Bounds(0, 0, pBitmap->Width, pBitmap->Height), clRed); // render bitmap
    Offset += pBitmap->Width + 4;   // add four pixels between bitmap and text
  }
  // display the text
  pCanvas->TextOut(Rect.Left + Offset, Rect.Top, (dynamic_cast<TListBox *>(Control))->Items->Strings[Index]);
}

Delphi Examples:

Copy Code

{
Here is a typical handler for an OnDrawItem event. In the
example, a list box with the lbOwnerDrawFixed style draws a
bitmap to the left of each string.
Select the TListBox and set the ItemHeight property to 32.
Select the ImageList and set the Layout Height and Width to
32.  Double click on the ImageList to load the images.  Be
sure to load in the correct order, logo2, Sunflower,
butterfly.
}
procedure TForm1.FormCreate(Sender: TObject);
begin
  MyList := TStringList.Create;
  bitmap0 := TBitmap.Create;
  bitmap1 := TBitmap.Create;
  bitmap2 := TBitmap.Create;
//  MyList.Add('Animal');
//  MyList.Add('Flowers');
//  MyList.Add('Butterfly');
//  ListBox1.Items.AddStrings(MyList);

  ImageList1.GetBitmap(0, bitmap0);
  ListBox1.Items.AddObject('Flowers', bitmap0);
  ImageList1.GetBitmap(1, bitmap1);
  ListBox1.Items.AddObject('Animal', bitmap1);
  ImageList1.GetBitmap(2, bitmap2);
  ListBox1.Items.AddObject('Butterfly', bitmap2);
end;

procedure TForm1.ListBox1DrawItem(Control: TWinControl; Index: Integer; Rect:TRect; State: TOwnerDrawState);
var
  Bitmap: TBitmap;      { temporary variable for the item’s bitmap }
  Offset: Integer;      { text offset width }
begin
  Bitmap := TBitmap.Create;
  with (Control as TListBox).Canvas do  { draw on control canvas, not on the form }
  begin
    FillRect(Rect);       { clear the rectangle }
    Offset := 2;          { provide default offset }
    Bitmap := TBitmap((Control as TListBox).Items.Objects[Index]);  { get the bitmap }
    if Bitmap <> nil then
    begin
      BrushCopy(
        Bounds(Rect.Left + Offset, Rect.Top, Bitmap.Width, Bitmap.Height),
        Bitmap, 
        Bounds(0, 0, Bitmap.Width, Bitmap.Height), 
        clRed);  {render bitmap}
      Offset := Bitmap.width + 6;    { add four pixels between bitmap and text}
    end;
    TextOut(Rect.Left + Offset, Rect.Top, (Control as TListBox).Items[Index])  { display the text }
  end;
end;