TList: what changed

Revision 0 to 1. Removed lines have a minus sign; added lines have a plus sign.

Title: TList

New		Line
1	+	## TList or TFPList
2	+
3	+	TList is a class that can be used to manage collections of pointers. It introduces methods and properties to store the pointers, search in the list of pointers, sort them. It manages its memory by itself, no intervention for that is needed (but, of course, it does not manage the memory of what ever your pointers point to). It has an event notification mechanism which allows to notify of list changes. This slows down some of TList mechanisms, and if no notification is used, TFPList may be used instead.
4	+
5	+	Both TList and TFPList are declared in classes and that usually is already in your uses clause.
6	+
7	+	The 'managed pointers' may conveniently point to, for example, records, just about any record you care to define.
8	+
9	+	Here is a very basic unit that will manage a set of notes about some friends of mine -
10	+
11	+	``` pascal
12	+	type
13	+	PNote=^TNote;
14	+	TNote = record
15	+	Name : ANSIString;
16	+	IsSilly : boolean;
17	+	NumbHeads : integer;
18	+	end;
19	+
20	+	type
21	+	// Note we can use TFPList (faster) or TList (and get event notification)
22	+	TNoteList = class(TList)
23	+	private
24	+	function Get(Index: integer): PNote;
25	+	public
26	+	destructor Destroy; override;
27	+	function Add(ANote : PNote) : integer;
28	+	function FindName(const Name : ANSIString) : PNote;
29	+	property Items[Index: integer]: PNote read Get; default;
30	+	end;
31	+
32	+	implementation
33	+
34	+	function TNoteList.Get(Index: integer): PNote;
35	+	begin
36	+	Result := PNote(inherited get(Index));
37	+	end;
38	+
39	+	function TNoteList.Add(ANote: PNote): integer;
40	+	begin
41	+	result := inherited Add(ANote);
42	+	end;
43	+
44	+	function TNoteList.FindName(const Name: ANSIString): PNote;
45	+	var
46	+	P : PNote;
47	+	begin
48	+	Result := Nil;
49	+	for P in self do
50	+	if P^.Name = Name then exit(P);
51	+	end;
52	+
53	+	destructor TNoteList.Destroy;
54	+	var
55	+	I : integer;
56	+	begin
57	+	for I := 0 to Count-1 do begin
58	+	dispose(Items[I]);
59	+	end;
60	+	inherited Destroy;
61	+	end;
62	+	....
63	+	```
64	+
65	+	In this example, that can use either TList or TFPList, we make a record that will hold one "item of data", and, to make things easy, we also declare a type pointer to that sort of record. Its sensible to put code like this in its own unit, a practical use will almost certainly require a few extra methods to manage the data it self.
66	+
67	+	To use this example, we need to declare a variable of type TNoteList and then create and destroy it. So, perhaps in a FormCreate we would have -
68	+
69	+	``` pascal
70	+	NoteList := TNoteList.Create;
71	+	```
72	+
73	+	and in FormDestroy we might have -
74	+
75	+	``` pascal
76	+	NoteList.free;
77	+	```
78	+
79	+	To load some data we would perhaps use -
80	+
81	+	``` pascal
82	+
83	+	procedure AddNote(N: string; Silly: boolean; NHeads: integer);
84	+	var
85	+	aPRec : PNote; // Not a record, just a pointer to one.
86	+	begin
87	+	new(aPRec);
88	+	aPRec^.Name := N;
89	+	aPRec^.IsSilly := Silly;
90	+	aPRec^.NumbHeads := NHeads;
91	+	NoteList.Add(aPRec);
92	+	end;
93	+
94	+	procedure TForm1.LoadData();
95	+	begin
96	+	AddNote('Joe', False, 1);
97	+	AddNote('Harry', True, 1);
98	+	AddNote('David', True, 2); // Tasmanian
99	+	AddNote('Boris', False, 1);
100	+	end;
101	+	```
102	+
103	+	and to use that data we might have -
104	+
105	+	``` pascal
106	+	procedure TForm1.UseData();
107	+	var
108	+	P : PNote; // P is a pointer to a note record, somewhere !
109	+	begin
110	+	P := NoteList.FindName('David');
111	+	if P <> nil then
112	+	writeln('David has ' + P^.NumbHeads.ToString + ' heads');
113	+	for P in NoteList do
114	+	if P^.IsSilly then
115	+	writeln(P^.Name + ' is silly');
116	+	if NoteList.FindName('George') = nil then
117	+	writeln('George is not listed');
118	+	end;
119	+	```
120	+
121	+	## See also
122	+
123	+	- [[Data Structures, Containers, Collections]]
124	+	- An [[AVL Tree]] will be faster.
125	+
126	+	---
127	+	From the Free Pascal wiki, page "TList", as it stood on 2023-10-24 after a change by Bart, 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).
128	+	Category: FPC
129	+	Category: RTL

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