Adding event to a runtime component

[justnewbie]

Guys, can you fix my code? Couldn't give an OnMouseUp event to it, doesn't compile.

Code: Pascal  [Select][+][-]

1. unit Unit1;
2.  
3. {$mode objfpc}{$H+}
4.  
5. interface
6.  
7. uses
8.   Classes, SysUtils, Forms, Controls, Graphics, Dialogs, StdCtrls, ExtCtrls, LCLIntf;
9.  
10. type
11.  
12.   { TForm1 }
13.  
14.   TForm1 = class(TForm)
15.     Button1: TButton;
16.     ColorDialog1: TColorDialog;    
17.     procedure Button1Click(Sender: TObject);
18.     procedure ShapeMouseUp(Sender: TObject; Button: TMouseButton;
19.       Shift: TShiftState; X, Y: Integer);
20.   private
21.  
22.   public
23.  
24.   end;
25.  
26. var
27.   Form1: TForm1;
28.  
29. implementation
30.  
31. {$R *.lfm}
32.  
33. { TForm1 }
34.  
35.  
36. procedure TForm1.Button1Click(Sender: TObject);   // Make empty palette
37. var  shape: TShape;
38. begin
39.      shape := TShape.Create(Self);
40.      shape.Parent := Form1;
41.      shape.Left := 100;
42.      shape.Top := 100;
43.      shape.Width := 20;
44.      shape.Height := 20;
45.      shape.Pen.Width := 1;
46.      shape.Pen.Color:=clBlack;
47.      shape.Brush.Color:=clDefault;
48.      shape.Visible := True;
49.      shape.Enabled := True;
50.  
51.      shape.OnMouseUp := ShapeMouseUp;
52. end;
53.  
54. procedure TForm1.ShapeMouseUp(Sender: TObject; Button: TMouseButton;
55.   Shift: TShiftState; X, Y: Integer);
56. begin
57.    if ColorDialog1.Execute then
58.    (Sender as TShape).Brush.Color:=ColorDialog1.Color;
59. end;
60.  
61. end.

[howardpc]

You need an "@" for objfpc mode

Code: Pascal  [Select][+][-]

1. shape.OnMouseUp := @ShapeMouseUp;

[justnewbie]

You need an "@" for objfpc mode

Code: Pascal  [Select][+][-]

1. shape.OnMouseUp := @ShapeMouseUp;

Great, it works! Thank you!
BTW, why the @ needed here? For the OnClick it doesn't need.

[Handoko]

Which OnClick did you mean?

If you want to pass a procedure as a variable then you need a @ symbol. It is not needed in Delphi Mode or if you use TypeAddressOn compiler switch.

Why do we need it? Because the syntax defines it so. That actually is a good thing, it can prevent programmers to do some stupid things.

Lazarus/FPC/Pascal is verbose and strict. Luckily all the rules can be found if you check the documentation:

https://wiki.lazarus.freepascal.org/@
https://www.freepascal.org/docs-html/user/usersu88.html#x132-1390007.3.3
https://www.freepascal.org/docs-html/prog/progsu76.html

[justnewbie]

Thank you, Handoko!