ListBox with separators: what changed

Revision 1 to 2. Removed lines have a minus sign; added lines have a plus sign.

Old	New		Line
1	1		The following sample code illustrates how dividing lines (separators) can be inserted between items in order to better group them. The text of items following a separator line must begin with a `'-'` character to define the divider. The listbox `Style` must be set to `lbOwnerDrawVariable` in order to activate owner-drawing with variable line heights: The `OnMeasureItem` event handler is responsible for the line height calculation; it must add a few pixels to the line height of the `'-'` carrying items to reserve space for the separators. And the `OnDrawItem` event handler must paint the separator line and remove the `'-'` from the separator-defining item text.
2	2
3		-	~~<figure>~~
4		-	~~<img src="listbox_dividers.png" title="listbox_dividers.png" />~~
5		-	~~<figcaption>listbox_dividers.png</figcaption>~~
6		-	~~</figure>~~
	3	+	![](/wiki-images/7/7a/Listbox_dividers.png)
7	4
8	5		``` pascal
9	6		unit Unit1;
10	7
11	8		{$mode objfpc}{$H+}
12	9
13	10		interface
14	11
15	12		uses
16	13		Classes, SysUtils, Forms, Controls, Graphics, Dialogs, StdCtrls, Types;
17	14
18	15		type
19	16
20	17		{ TForm1 }
21	18
22	19		TForm1 = class(TForm)
23	20		ListBox1: TListBox;
24	21		procedure FormCreate(Sender: TObject);
25	22		procedure ListBox1DrawItem(Control: TWinControl; Index: Integer;
26	23		ARect: TRect; State: TOwnerDrawState);
27	24		procedure ListBox1MeasureItem(Control: TWinControl; Index: Integer;
28	25		var AHeight: Integer);
29	26		private
30	27
31	28		public
32	29
33	30		end;
34	31
35	32		var
36	33		Form1: TForm1;
37	34
38	35		implementation
39	36
40	37		{$R *.lfm}
41	38
42	39		uses
43	40		LCLType;
44	41
45	42		{ TForm1 }
46	43
47	44		procedure TForm1.FormCreate(Sender: TObject);
48	45		begin
49	46		with ListBox1.Items do begin
50	47		Add('Paris');
51	48		Add('Rome');
52	49		Add('London');
53	50		Add('Berlin');
54	51		Add('-Casablanca');
55	52		Add('Cairo');
56	53		Add('Khartoum');
57	54		Add('Pretoria');
58	55		Add('-Tokyo');
59	56		Add('Beijing');
60	57		Add('Manila');
61	58		Add('-New York');
62	59		Add('Chicago');
63	60		Add('Rio de Janeiro');
64	61		Add('Lima');
65	62		Add('-');
66	63		end;
67	64		end;
68	65
69	66		const
70	67		MARGIN_LINE = 2;
71	68		MARGIN_TEXT = 12;
72	69		MARGIN_VERT = 2;
73	70		HLINE = 1;
74	71
75	72		procedure TForm1.ListBox1DrawItem(Control: TWinControl; Index: Integer;
76	73		ARect: TRect; State: TOwnerDrawState);
77	74		var
78	75		lb: TListbox;
79	76		s: String;
80	77		hasLine: Boolean;
81	78		dy: Integer;
82	79		begin
83	80		lb := Control as TListbox;
84	81		s := lb.Items[Index];
85	82		hasLine := (s <> '') and (s[1] = '-');
86	83		if hasLine then dy := HLINE else dy := 0;
87	84		lb.Canvas.Brush.Style := bsSolid;
88	85		lb.Canvas.Font.Assign(lb.Font);
89	86		if odSelected in State then
90	87		begin
91	88		if hasLine then
92	89		begin
93	90		lb.Canvas.Brush.Color := lb.Color;
94	91		lb.Canvas.FillRect(ARect.Left, ARect.Top, ARect.Right, ARect.Top+dy);
95	92		inc(ARect.Top, HLINE + 2);
96	93		end;
97	94		if lb.Focused then
98	95		lb.Canvas.Brush.Color := clHighlight
99	96		else
100	97		lb.Canvas.Brush.Color := clGray;
101	98		lb.Canvas.Font.Color := clHighlightText;
102	99		end else
103	100		begin
104	101		lb.Canvas.Brush.Color := lb.Color;
105	102		lb.Canvas.Font.Color := clWindowText;
106	103		dy := 0;
107	104		end;
108	105
109	106		lb.Canvas.FillRect(ARect);
110	107
111	108		if hasLine then
112	109		begin
113	110		if not (odSelected in State) then
114	111		begin
115	112		lb.Canvas.Pen.Style := psSolid;
116	113		lb.Canvas.Pen.Color := clWindowText;
117	114		lb.Canvas.Line(
118	115		ARect.Left + MARGIN_LINE,
119	116		ARect.Top + HLINE,
120	117		ARect.Right - MARGIN_LINE,
121	118		ARect.Top + HLINE
122	119		);
123	120		end;
124	121		Delete(s, 1, 1);
125	122		end;
126	123
127	124		lb.Canvas.Brush.Style := bsClear;
128	125		lb.Canvas.TextOut(
129	126		ARect.Left + MARGIN_TEXT,
130	127		(ARect.Top + dy + ARect.Bottom - lb.Canvas.TextHeight('Tg')) div 2,
131	128		s
132	129		);
133	130		end;
134	131
135	132		procedure TForm1.ListBox1MeasureItem(Control: TWinControl; Index: Integer;
136	133		var AHeight: Integer);
137	134		var
138	135		lb: TListbox;
139	136		h: Integer;
140	137		s: String;
141	138		begin
142	139		lb := Control as TListBox;
143	140		lb.Canvas.Font.Assign(lb.Font);
144	141		h := lb.Canvas.TextHeight('Tg') + MARGIN_VERT * 2;
145	142		s := lb.Items[Index];
146	143		if (s <> '') and (s[1] = '-') then
147	144		inc(h, HLine);
148	145		AHeight := h;
149	146		end;
150	147
151	148		end.
152	149		```
153	150
154	151		---
155	152		From the Free Pascal wiki, page "ListBox with separators", as it stood on 2023-08-19 after a change by Wp, out of the wiki's dump of 2024-05-26. Copyright stays with the author who wrote it, according to the old wiki's [[Licensing]] page. If you have concerns about this material, [message the admin](/wiki-contact).
156	153		Category: Code Snippets

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