TButton: what changed

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Title: TButton

New		Line
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	+
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.
4	+
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	+
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	+
9	+	``` pascal
10	+	procedure TForm1.Button1Click(Sender: TObject);
11	+	begin
12	+
13	+	end;
14	+	```
15	+
16	+	Between the [[statement\|statements]] [[Begin\|begin]] and [[End\|end]] you could write code that is called when Button1 is clicked.
17	+
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:
19	+
20	+	- [[Form Tutorial\|The first GUI application]] for absolute beginners
21	+	- [[Lazarus Tutorial\|Your first Lazarus program]] tutorial for Lazarus
22	+	- [[Object Oriented Programming with FreePascal and Lazarus\|Programming Example]] Object Oriented Programming with Free Pascal and Lazarus
23	+
24	+	## A simple example
25	+
26	+	- Create a new application and drop a TButton on the form.
27	+	- Doubleclick this Button1 on the form (the default handler: OnClick is created for Button1, the source text editor opens).
28	+	- Add following code in the event handler:
29	+
30	+	``` pascal
31	+	procedure TForm1.Button1Click(Sender: TObject);
32	+	begin
33	+	ShowMessage('Lazarus makes my day'); //A message will be displayed with the content...
34	+	end;
35	+	```
36	+
37	+	- Start your program (with Key <span class="kbd">F9</span>).
38	+
39	+	## Right-click
40	+
41	+	Each TButton has an (optional) PopupMenu [[Property\|property]] that will activate a connected [[TPopupMenu]] whenever the button is right-clicked.
42	+
43	+	## Dynamically generated button
44	+
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.
46	+
47	+	This can be achieved as in the the following example (a quick calculator):
48	+
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	+	- Change caption Form1 to QuickAdd.
51	+	- Create the OnCreate event handler of Form1 (go in the Object Inspector to the event OnCreate and click the button \[...\]).
52	+	- Add following code:
53	+
54	+	``` pascal
55	+	procedure TForm1.FormCreate(Sender: TObject);
56	+	var
57	+	i: Integer;
58	+	aButton: TButton;
59	+	begin
60	+	for i := 0 to 9 do begin // create 10 Buttons
61	+	aButton := TButton.Create(Self); // create Button, Owner is Form1, where the button is released later
62	+	aButton.Parent := Self; // determine where it is to be displayed
63	+	aButton.Width := aButton.Height; // Width should correspond to the height of the buttons
64	+	aButton.Left := i * aButton.Width; // Distance from left
65	+	aButton.Caption := IntToStr(i); // Captions of the buttons (0.9)
66	+	aButton.OnClick := @aButtonClick; // the event handler for the button -> will be created yet
67	+	end;
68	+	Self.Height := aButton.Height; // Height of the form should correspond to the height of the buttons
69	+	Self.Width := aButton.Width * 10; // Width of the form to match the width of all buttons
70	+	end;
71	+	```
72	+
73	+	- Now you must create the event handler for the button clicks.
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);`.
76	+	- Paste following code:
77	+
78	+	``` pascal
79	+	procedure TForm1.aButtonClick(Sender: TObject);
80	+	const
81	+	Cnt: Integer = 0;
82	+	var
83	+	i: Integer;
84	+	begin
85	+	if (Sender is TButton) and // called the event handler of a button out?
86	+	TryStrToInt(TButton(Sender).Caption, i) // then try to convert the label in a integer
87	+	then begin
88	+	Cnt := Cnt + i; // the adding counter is incremented by the number of entrechende
89	+	Caption:='QuickAdd: '+IntToStr(Cnt); // write the result to the caption of the form
90	+	end;
91	+	end;
92	+	```
93	+
94	+	- Start your application.
95	+
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	+
98	+	## See also
99	+
100	+	- [[doc:lcl/stdctrls/tbutton.html\|TButton doc]]
101	+	- [[TBitBtn]]
102	+	- [[TSpeedButton]]
103	+	- [[TColorButton]]
104	+	- [[15-puzzle]] (Game)
105	+
106	+	---
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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