OnDrawItem (Delphi)

Description

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 the ImageList to load the images. Be sure to load in the correct order: logo2, Sunflower, butterfly.

Code

procedure TForm1.FormCreate(Sender: TObject);
begin
  MyList := TStringList.Create;
  bitmap0 := TBitmap.Create; // These objects are created without an owner, so they must be explicitly deleted.
  bitmap1 := TBitmap.Create; // They are added to an ImageList, which also will not delete them when it is destroyed.
  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); // Adding bitmap0 to an ImageList does not copy bitmap0.
  ImageList1.GetBitmap(1, bitmap1);             // So, you can't destroy bitmap0 as long as the image list needs it.
  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;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  MyList.Free;
  bitmap0.Free;
  bitmap1.Free;
  bitmap2.Free;
end;

Uses

• Vcl.StdCtrls.TCustomListBox.OnDrawItem ( fr | de | ja )
• Vcl.StdCtrls.TCustomListBox.Canvas ( fr | de | ja )