TButton: what changed

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

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1	1		A TButton ![](/wiki-images/b/b2/Tbutton.png) is a component that provides a basic push button control. It is available on the [[Standard tab]] of the [[Component Palette]].
2	2
3		-	A TButton is one of the most basic controls on a [[TForm\|Form]]. Clicking with the mouse on it (or change with the <span class="kbd">Tab</span> key on the button and pressed it with <span class="kbd">Enter</span>), an action is triggered. This click is called an event. For this you need [[Event order\|event handler]] that are called after the jump.
	3	+	A TButton is one of the most basic controls on a [[TForm\|Form]]. Clicking with the mouse on it (or change with the `Tab` key on the button and pressed it with `Enter`), an action is triggered. This click is called an event. For this you need [[Event order\|event handler]] that are called after the jump.
4	4
5	5		You can add a button to your form, by clicking the TButton (square button with an "OK" in the middle ![](/wiki-images/b/b2/Tbutton.png)) on the Standard component palette and place it with a click on your form.
6	6
7	7		The event handler for a mouse click can be quite easily reached in which a double-click on the pasted Button (or in the Object Inspector, select the event OnClick of your Button). The event handler for a Button1 on a form Form1 will look like this:
8	8
9	9		``` pascal
10	10		procedure TForm1.Button1Click(Sender: TObject);
11	11		begin
12	12
13	13		end;
14	14		```
15	15
16	16		Between the [[statement\|statements]] [[Begin\|begin]] and [[End\|end]] you could write code that is called when Button1 is clicked.
17	17
18	18		Almost all available beginner tutorials use TButtons as an easy entry into the [[object-oriented programming\|Object Oriented Programming]] with Lazarus. Following tutorials are well suited for beginners to understand the use of buttons:
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20	20		- [[Form Tutorial\|The first GUI application]] for absolute beginners
21	21		- [[Lazarus Tutorial\|Your first Lazarus program]] tutorial for Lazarus
22	22		- [[Object Oriented Programming with FreePascal and Lazarus\|Programming Example]] Object Oriented Programming with Free Pascal and Lazarus
23	23
24	24		## A simple example
25	25
26	26		- Create a new application and drop a TButton on the form.
27	27		- Doubleclick this Button1 on the form (the default handler: OnClick is created for Button1, the source text editor opens).
28	28		- Add following code in the event handler:
29	29
30	30		``` pascal
31	31		procedure TForm1.Button1Click(Sender: TObject);
32	32		begin
33	33		ShowMessage('Lazarus makes my day'); //A message will be displayed with the content...
34	34		end;
35	35		```
36	36
37		-	~~- Start your program (with Key <span class="kbd">F9</span>).~~
	37	+	- Start your program (with Key `F9`).
38	38
39	39		## Right-click
40	40
41	41		Each TButton has an (optional) PopupMenu [[Property\|property]] that will activate a connected [[TPopupMenu]] whenever the button is right-clicked.
42	42
43	43		## Dynamically generated button
44	44
45	45		Sometimes, instead of creating buttons (or other components) with the Lazarus form designer, it is easier to create them dynamically at [[runtime\|run time]]. This approach is useful especially if you have continually repeated buttons on a form.
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47	47		This can be achieved as in the the following example (a quick calculator):
48	48
49	49		- Create a new blank [[Form Tutorial\|GUI application]] with the form Form1 and add StdCtrls to the [[Uses\|uses clause]] (here the TButton is).
50	50		- Change caption Form1 to QuickAdd.
51	51		- Create the OnCreate event handler of Form1 (go in the Object Inspector to the event OnCreate and click the button \[...\]).
52	52		- Add following code:
53	53
54	54		``` pascal
55	55		procedure TForm1.FormCreate(Sender: TObject);
56	56		var
57	57		i: Integer;
58	58		aButton: TButton;
59	59		begin
60	60		for i := 0 to 9 do begin // create 10 Buttons
61	61		aButton := TButton.Create(Self); // create Button, Owner is Form1, where the button is released later
62	62		aButton.Parent := Self; // determine where it is to be displayed
63	63		aButton.Width := aButton.Height; // Width should correspond to the height of the buttons
64	64		aButton.Left := i * aButton.Width; // Distance from left
65	65		aButton.Caption := IntToStr(i); // Captions of the buttons (0.9)
66	66		aButton.OnClick := @aButtonClick; // the event handler for the button -> will be created yet
67	67		end;
68	68		Self.Height := aButton.Height; // Height of the form should correspond to the height of the buttons
69	69		Self.Width := aButton.Width * 10; // Width of the form to match the width of all buttons
70	70		end;
71	71		```
72	72
73	73		- Now you must create the event handler for the button clicks.
74	74		- In the source editor, entering your [[Class\|class]] TForm1 in the section [[Private\|private]].
75		-	- Add `procedure aButtonClick(Sender: TObject);` and then press the keys <span class="kbd">Ctrl</span>+<span class="kbd">Shift</span>+<span class="kbd">c</span> (the code completion becomes active and creates the [[Procedure\|procedure]] `TForm1.aButtonClick(Sender: TObject);`.
	75	+	- Add `procedure aButtonClick(Sender: TObject);` and then press the keys `Ctrl`+`Shift`+`c` (the code completion becomes active and creates the [[Procedure\|procedure]] `TForm1.aButtonClick(Sender: TObject);`.
76	76		- Paste following code:
77	77
78	78		``` pascal
79	79		procedure TForm1.aButtonClick(Sender: TObject);
80	80		const
81	81		Cnt: Integer = 0;
82	82		var
83	83		i: Integer;
84	84		begin
85	85		if (Sender is TButton) and // called the event handler of a button out?
86	86		TryStrToInt(TButton(Sender).Caption, i) // then try to convert the label in a integer
87	87		then begin
88	88		Cnt := Cnt + i; // the adding counter is incremented by the number of entrechende
89	89		Caption:='QuickAdd: '+IntToStr(Cnt); // write the result to the caption of the form
90	90		end;
91	91		end;
92	92		```
93	93
94	94		- Start your application.
95	95
96	96		> Note: You can assign every imaginable event handlers to your buttons, as long as this the form `procedure <class>.<name of procedure>(Sender: TObject);` has. Thus, you can use one from another class!
97	97
98	98		## See also
99	99
100	100		- [[doc:lcl/stdctrls/tbutton.html\|TButton doc]]
101	101		- [[TBitBtn]]
102	102		- [[TSpeedButton]]
103	103		- [[TColorButton]]
104	104		- [[15-puzzle]] (Game)
105	105
106	106		---
107	107		From the Free Pascal wiki, page "TButton", as it stood on 2019-11-09 after a change by Djzepi, 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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