[SOLVED] Learning Procedural Type

[tudi_x]

hi All,
i started to learn procedural types as for the managing of several objects i would like to implement a simpler mechanism, something modeled in the below and attached.
basically from Button2 i would like to change the method on the click event for Button1 through a procedural approach and using an array of structures.
the below does not work but is there a way to make it work?
please advise.
thank you

Code: Pascal  [Select][+][-]

1. unit Unit1;
2.  
3. {$mode objfpc}{$H+}
4.  
5. interface
6.  
7. uses
8.   Classes, SysUtils, FileUtil, Forms, Controls, Graphics, Dialogs, StdCtrls;
9.  
10. type
11.   TAction = procedure(AMessage: string) of object;
12.  
13. type
14.   TStepInfo = record
15.     Name: string;
16.     Action: TAction;
17.   end;
18.  
19. type
20.   TSteps = array of TStepInfo;
21.  
22. type
23.   TForm1 = class(TForm)
24.     Button1: TButton;
25.     Button2: TButton;
26.     Memo1: TMemo;
27.     procedure Button2Click(Sender: TObject);
28.     procedure FormCreate(Sender: TObject);
29.   private
30.     s: TSteps;
31.     step_id: word;
32.     procedure Step1(AMessage: string);
33.     procedure Step2(AMessage: string);
34.   public
35.  
36.   end;
37.  
38. var
39.   Form1: TForm1;
40.  
41. implementation
42.  
43. {$R *.lfm}
44.  
45. procedure TForm1.FormCreate(Sender: TObject);
46. begin
47.   step_id := 0;
48.  
49.   s[1].Name := 'msg1';
50.   s[1].Action := Step1(s[1].Name); //unit1.pas(53,18) Error: Incompatible types: got "untyped" expected "<procedure variable type of procedure(AnsiString) of object;Register>"
51.  
52.   s[2].Name := 'msg2';
53.   s[2].Action := Step2(s[2].Name);
54. end;
55.  
56. procedure TForm1.Button2Click(Sender: TObject);
57. begin
58.   step_id := step_id + 1;
59.   Button1.OnClick := @s[step_id].Action; //unit1.pas(62,22) Error: Incompatible types: got "Pointer" expected "<procedure variable type of procedure(TObject) of object;Register>"
60. end;
61.  
62. procedure TForm1.Step1(AMessage: string);
63. begin
64.   Memo1.Append('step 1: ' + AMessage);
65. end;
66.  
67. procedure TForm1.Step2(AMessage: string);
68. begin
69.   Memo1.Append('step 2: ' + AMessage);
70. end;
71.  
72. end.

[Eugene Loza]

First of all, you have to provide a reference (pointer) to the procedural type.
i.e. not
s[1].Action := Step1(s[1].Name);
but
s[1].Action := @Step1;
(note the "@" symbol which means that @Step1 is a pointer/reference to Step1).

As you've also noticed you can't pass parameters to a pointer.
E.g.

Code: Pascal  [Select][+][-]

1. type TProcedure = procedure(a: integer);
2. Proc: TProcedure;
3.  
4. procedure MyProc(a: integer);
5. begin
6.   writeln(a);
7. end;
8.  
9. ...
10.  
11. Proc := @MyProc; //assign a procedural variable;
12.  
13. Proc(a); //Call the assigned procedure with the parameter specified.

[Eugene Loza]

The second procedure:
Button1.OnClick := @s[step_id].Action
You also can't assign OnClick which is procedure(Sender: TObject) of object to procedure(AMessage: string) of object - they have different parameter - TObject in the first case and String in the second. As far as you don't want to change Lazarus source code to change the OnClick definition, you have to provide it with a valid procedure(Sender: TObject) of object procedure reference.
P.S. you don't need the @ symbol here, as Action is TAction which is already a reference and "reference to a reference" will not work as expected.

[molly]

It seems there is also another misunderstanding from tudi_x.

The onCLick event from a tbutton has the following declaration:

Code: [Select]

public property TControl.OnClick: TNotifyEvent  read FOnClick  write FOnClick  stored IsOnClickStored;

So, looking at TNotifyEvent that reads:

Code: [Select]

type TNotifyEvent = procedure(Sender: TObject) of object

And alas that does not match:

Code: [Select]

type
  TAction = procedure(AMessage: string) of object;

So that the assignment:

Code: [Select]

  Button1.OnClick := @s[step_id].Action;
Wil fail as the two declarations differ.

edit: Ah, beaten by Eugene Loza 

[howardpc]

Also note that dynamic arrays require a SetLength() before use, and are indexed from zero (not 1).
Try the attached project.

[tudi_x]

thank you guys!
changed the code to:

Code: Pascal  [Select][+][-]

1. unit main;
2.  
3. {$mode objfpc}{$H+}
4.  
5. interface
6.  
7. uses
8.   Classes, SysUtils, FileUtil, Forms, Controls, Graphics, Dialogs, StdCtrls,
9.   Buttons, typinfo;
10.  
11. type
12.   TStepsEnum = (the_step0, the_step1, the_step2);
13.  
14. type
15.   TAction = procedure(ASender: TObject) of object;
16.  
17. type
18.   TStepInfo = record
19.     Name: string;
20.     Action: TAction;
21.   end;
22.  
23. type
24.   TSteps = array of TStepInfo;
25.  
26. type
27.   TForm1 = class(TForm)
28.     BitBtn1: TBitBtn;
29.     Button1: TButton;
30.     Button2: TButton;
31.     Memo1: TMemo;
32.     procedure BitBtn1Click(Sender: TObject);
33.     procedure Button2Click(Sender: TObject);
34.     procedure FormCreate(Sender: TObject);
35.   private
36.     s: TSteps;
37.     step_id: word;
38.     procedure Step0(ASender: TObject);
39.     procedure Step1(ASender: TObject);
40.     procedure Step2(ASender: TObject);
41.   public
42.  
43.   end;
44.  
45. var
46.   Form1: TForm1;
47.  
48. implementation
49.  
50. {$R *.lfm}
51.  
52. procedure TForm1.FormCreate(Sender: TObject);
53. begin
54.   step_id := 0;
55.   SetLength(s, Ord(High(TStepsEnum)) + 1);
56.  
57.   s[0].Name := GetEnumName(TypeInfo(TStepsEnum), Ord(0));
58.   s[0].Action := @Step0;
59.  
60.   s[1].Name := GetEnumName(TypeInfo(TStepsEnum), Ord(1));
61.   s[1].Action := @Step1;
62.  
63.   s[2].Name := GetEnumName(TypeInfo(TStepsEnum), Ord(2));
64.   s[2].Action := @Step2;
65. end;
66.  
67. procedure TForm1.Button2Click(Sender: TObject);
68. begin
69.   Button1.OnClick := s[step_id].Action;
70. end;
71.  
72. procedure TForm1.BitBtn1Click(Sender: TObject);
73. begin
74.   step_id := step_id + 1;
75. end;
76.  
77. procedure TForm1.Step0(ASender: TObject);
78. begin
79.   Memo1.Append('id: ' + IntToStr(step_id) + 'step 0: ' + s[step_id].Name);
80. end;
81.  
82. procedure TForm1.Step1(ASender: TObject);
83. begin
84.   Memo1.Append('step 1: ' + s[step_id].Name);
85. end;
86.  
87. procedure TForm1.Step2(ASender: TObject);
88. begin
89.   Memo1.Append('step 2: ' + s[step_id].Name);
90. end;
91.  
92. end.

[howardpc]

You seem to have got the idea!

Note that High(array) returns an ordinal number, so does not need Ord(). Also, "type" can introduce a series of type definitions, so does not need to be repeated.