Mega Code Archive
How to display an alternating color for each TListBox row
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Title: How to display an alternating color for each TListBox row
unit Unit1;
interface
uses
Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
StdCtrls;
type
TListbox = class(StdCtrls.TListbox)
private
procedure wmEraseBkGnd(var Msg: TWMEraseBkGnd); message WM_ERASEBKGND;
end;
TForm1 = class(TForm)
ListBox1: TListBox; // (!) ListBox1.Style := lbOwnerDrawFixed
Button1: TButton;
procedure Button1Click(Sender: TObject);
procedure ListBox1DrawItem(Control: TWinControl; Index: Integer;
Rect: TRect; State: TOwnerDrawState);
{ ... }
end;
var
Form1: TForm1;
implementation
{$R *.DFM}
procedure TForm1.Button1Click(Sender: TObject);
var
i: Integer;
begin
for i := listbox1.Items.Count to listbox1.Items.Count + 5 do
listbox1.Items.Add(Format('Item %d', [i]));
end;
{ TListbox }
const
colors: array [Boolean] of TColor = ($FFFFC0, $C0FFFF);
procedure TListbox.wmEraseBkGnd(var Msg: TWMEraseBkGnd);
var
cv: TCanvas;
h, max: Integer;
r: TRect;
b: Boolean;
begin
Msg.Result := 1;
h := Perform(LB_GETITEMHEIGHT, 0, 0);
if h = LB_ERR then h := ItemHeight;
cv := TCanvas.Create;
try
cv.Handle := Msg.DC;
r := Rect(0, 0, ClientWidth, h);
b := Odd(TopIndex) and (TopIndex = 0);
max := ClientHeight;
cv.Brush.Style := bsSolid;
while r.Top max do
begin
cv.Brush.Color := colors[b];
b := not b;
cv.FillRect(r);
OffsetRect(r, 0, h);
end;
finally
cv.Handle := 0;
cv.Free;
end;
end;
procedure TForm1.ListBox1DrawItem(Control: TWinControl; Index: Integer;
Rect: TRect; State: TOwnerDrawState);
var
cb, ct: TColor;
begin
if not (odSelected in State) then
with Control as TListbox do
begin
Canvas.Brush.Color := colors[Odd(Index)];
Canvas.Brush.Style := bsSolid;
end;
Rect.Right := Control.ClientWidth;
with Control as TListbox do
begin
Canvas.FillRect(Rect);
Canvas.Brush.Style := bsClear;
Canvas.TextRect(Rect, Rect.Left + 2, Rect.Top, Items[Index]);
end;
end;
end.
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