TListView: what changed

Revision 2 to 3. Removed lines have a minus sign; added lines have a plus sign.

Old	New		Line
1	1		TListView ![](/wiki-images/d/d7/Tlistview.png) is a visible component on the [[Common Controls tab]] of the [[Component Palette]] that provides a list view of its associated Items. Items can be represented by an icon from each of the associated [[TImageList\|TImageLists]]: SmallImages, LargeImages and StateImages.
2	2
3	3		## Notes
4	4
5	5		- GetNextItem() requires StartItem to be provided. This is incompatible with Delphi's GetNextItem(), where startItem is allowed to be nil, which will perform the search from the relative (direction driven) start.
6	6
7	7		## Sorting
8	8
9		-	~~`TODO: add description on how OwnerData affects the sorting`~~
	9	+	```text
	10	+	TODO: add description on how OwnerData affects the sorting
	11	+	```
10	12
11	13		Sorting is (typically?) applied when using vsReport ViewStyle, as it's column driven (with Sortcolumn index required). Sorting might be a time consuming for a larger data scale (when comparison of items takes a considerable time).
12	14
13	15		SortType is the key property in order to perform any sorting in TListView.
14	16
15	17
16	18		stNone - (the default value) that no sorting should be for the control.
17	19
18	20		stText - the text of a cells would be used for item comparison. The actual text entry is controlled by SortColumn property. Note the default sorting comparison is actually treats the text as Ansi, rather than UTF8. Thus the result might be undesired for the non-English texts
19	21
20	22		stData - the default sorting comparison treats Data property as an integer value (by casting pointer to an integer) and sorts the according to value. (in most cases such sorting is useless, unless "Data" is an actual integer casted to the pointer)
21	23
22	24		stBoth - treated as stText for in the default sorting comparison.
23	25
24	26		Unless using text sorting, the default comparison method is not the best approach, instead a custom comparison could be used. The custom comparison is assigned with OnCompare event of TListView. The following parameters are passed:
25	27
26	28
27	29		Sender - TListview that's being sorted
28	30
29	31		Item1 - one TListItem being compared
30	32
31	33		Item2 - another TListItem being compared to the one
32	34
33	35		Data - is not used and is always passed as zero. (provided for Delphi compatibility)
34	36
35	37		Compare - the result of the comparison, that must be populated by the event. The following values should be assigned to the Compare argument.
36	38
37	39
38	40		-1 - if Item1 should show up "earlier" in Ascending order, than Item2. (Item1 is less than Item2)
39	41
40	42		0 - if two items are equal
41	43
42	44		1 - if Item2 should show up "earlier" in Ascending order, than Item1. (Item2 is less than Item1)
43	45
44	46		It's a normal practice to reverse the comparison result value, if SortDirection is descending. I.e.:
45	47
46	48		```delphi
47	49		procedure TForm1.ListView1OnCompare(Sender: TObject; Item1, Item2: TListItem;
48	50		Data: Integer; var Compare: Integer)
49	51		begin
50	52		... do the comparison...
51	53
52	54		if TListView(Sender).SortDirection = sdDescending then
53	55		Compare := -Compare;
54	56		end;
55	57		```
56	58
57	59		The OnCompare event should check for SortType, SortColumn and SortDirection properties of TListView, and do adjust the comparison result respectively of those properties.
58	60
59	61		Method Sort performs of items, if SortType is other than stNone and SortColumn is assigned to a valid column index.
60	62
61	63		Method CustomSort performs a one-time sorting using a provided sorting function.
62	64
63	65
64	66		ASortProc: TLVCompare - sorting function
65	67
66	68		AOptionalParam: PtrInt - sorting parameter
67	69
68	70		Sorting parameter is ignored (provided for the Delphi compatibility). If ASortProc is passed as nil, then the either sorting OnCompare is used or default sorting.
69	71
70	72		Typically the sorting can be requested by a user. Whenever a user clicks on a column header, that requires to either sort (initially ascendancy) or to switch to the opposite sorting order (either from ascendant to descendant, or back). It's not a rule, but a common expectation. For some data sets selecting sorting might not make any sense. AutoSort (default value is true)the property of TListview controls, if the listview should be sorted automatically, as soon as user clicks on a column header. AutoSort will have no effect, while SortType is set to stNone.
71	73
72	74		AlphaSort is a convenience method, that changes the settings to ascending sort (SortDirection=sdAscending) based on the text (SortType=stText) of the first column (SortColumn=0). Note that the actual properties are changed.
73	75
74	76		### Sort Indicator
75	77
76	78		Originating from: <https://bugs.freepascal.org/view.php?id=36281>
77	79
78	80		In trunk since r62567
79	81
80	82		1\) Add a new property SortIndicator to TListViewColumn. The property controls system native sort indicator.
81	83
82	84		The indicator is acting solely as a decorative feature. (Doesn't have any effect on the sorting). The indicator has 3 possible values
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84	86
85	87		siNone - no sort indicator should be shown
86	88
87	89		siAscending - ascending indicator should be shown
88	90
89	91		siDescending - descending indicator should be shown
90	92
91	93		The property can work independently of other TListview sorting properties.
92	94
93	95		![](/wiki-images/2/29/Autosort0.gif)
94	96
95	97		2\) Add new property AutoSortIndicator to TListView. The property is intended to be used as a compliment to AutoSort property. If both are enabled, LCL code controls the current selection of the column sortindicator according to AutoSort rules.
96	98
97	99		![](/wiki-images/7/78/Autosort2.gif)
98	100
99	101		Early 2021 it was noticed that if you are using Qt5 and you have TListView.SortDirection set to sdAscending (the default), then setting a column's Sort Indicator to siDescending displays an ascending indicator. This does not happen with GTK2 or GTK3. Setting SortDirection to sdDescending makes all other combinations work fine so, seems an easy solution. Logged <https://bugs.freepascal.org/view.php?id=38393>
100	102
101	103		## Custom drawing
102	104
103	105		There is a good article on custom-drawing `TListView`: <https://delphidabbler.com/articles/article-16>. Most of the sample code in this article is working in Lazarus, too, however only on Windows. Here are some excerpts:
104	106
105	107		Note: Keep the `OwnerDraw` property of the `TListView` at `false`.
106	108
107	109		### Alternating row colors
108	110
109	111		![](/wiki-images/7/70/Listview_alternating_rowcolors.png) Attach this handler for the `OnCustomDrawItem` event which is responsible for painting a full row. When the `DefaultDraw` parameter of the event handler is unchanged (i.e., `true`) then control still paints the text and additional gimmicks such as icons or checkboxes (see screenshot at the right):
110	112
111	113		``` Pascal
112	114		procedure TForm1.ListView1CustomDrawItem(Sender: TCustomListView;
113	115		Item: TListItem; State: TCustomDrawState; var DefaultDraw: Boolean);
114	116		begin
115	117		if Odd(Item.Index) then
116	118		// odd list items have green background
117	119		ListView1.Canvas.Brush.Color := clMoneyGreen
118	120		else
119	121		// even list items have window colour background
120	122		ListView1.Canvas.Brush.Color := clWindow;
121	123		end;
122	124		```
123	125
124	126		### Individual column colors
125	127
126	128		At first prepare a procedure to set the brush color for each ListView column:
127	129
128	130		``` Pascal
129	131		{ Sets the brush colour for the column. Our ListView has 3 columns }
130	132		procedure TForm1.SetLVColumnColour(AColIndex: Integer);
131	133		const
132	134		cRainbow: array[0..2] of TColor = ($FFCCCC, $CCFFCC, $CCCCFF);
133	135		begin
134	136		ListView1.Canvas.Brush.Color := cRainBow[AColumnIndex];
135	137		end;
136	138		```
137	139
138	140		Then provide a handler of the `OnCustomDrawItem` event which is responsible for painting of the entire row and, in particular, of the 1st column, and the `OnCustomDrawSubItem` event which is called when the other columns are painted: ![](/wiki-images/1/1d/Listview_different_column_colors.png)
139	141
140	142		``` Pascal
141	143		{ Draw the "Caption" column }
142	144		procedure TForm1.ListView1CustomDrawItem(Sender: TCustomListView;
143	145		Item: TListItem; State: TCustomDrawState; var DefaultDraw: Boolean);
144	146		begin
145	147		SetLVColumnColour(0);
146	148		end;
147	149
148	150		{ Draw the sub item columns }
149	151		procedure TForm1.ListView1CustomDrawSubItem(Sender: TCustomListView;
150	152		Item: TListItem; SubItem: Integer; State: TCustomDrawState;
151	153		var DefaultDraw: Boolean);
152	154		begin
153	155		SetLVColumnColour(SubItem);
154	156		end;
155	157		```
156	158
157	159		## Widgetset Implementation
158	160
159	161		ListView is implemented via TWSCustomListViewClassinterface.
160	162
161	163		Method
162	164
163	165		Description
164	166
165	167		SelectAll
166	168
167	169		The method provides a parameter AIsSet.
168	170
169	171		If the parameter is set to true then all items should selected in the view. If it's false then, all parameters should deselected.
170	172
171	173		It's important that the event shouldn't trigger any events, as LCL will call SelectChange event by itself.
172	174
173	175		## See also
174	176
175	177		- [[doc:lcl/comctrls/tlistview.html\|Doc. TListView]]
176	178		- [[TTreeView]]
177	179		- [[TShellListView]]
178	180
179	181		---
180	182		From the Free Pascal wiki, page "TListView", as it stood on 2023-04-28 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).

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