Overriding of click method don't work in TreeView

[simsee]

If I override the click method of a TButton, when the control is clicked, the code of that method is executed, as I expect:

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;
9.  
10. type
11.  
12.   { TButton }
13.  
14.   TButton=class(StdCtrls.TButton)
15.     procedure Click; override;
16.   end;
17.  
18.   { TForm1 }
19.  
20.   TForm1 = class(TForm)
21.     procedure FormCreate(Sender: TObject);
22.   private
23.     Button : TButton;
24.   public
25.  
26.   end;
27.  
28. var
29.   Form1: TForm1;
30.  
31. implementation
32.  
33. {$R *.lfm}
34.  
35. { TButton }
36.  
37. procedure TButton.Click;
38. begin
39.   inherited Click;
40.   writeln('Click');
41. end;
42.  
43. { TForm1 }
44.  
45. procedure TForm1.FormCreate(Sender: TObject);
46. begin
47.   Button:=TButton.Create(self);
48.   Button.Parent:=self;
49. end;
50.  
51. end.

If I override the click method of a TTreeView, when the control is clicked, the code of that method is not executed:

Code: Pascal  [Select][+][-]

1. unit Unit1;
2.  
3. {$mode objfpc}{$H+}
4.  
5. interface
6.  
7. uses
8.   Classes, SysUtils, Forms, Controls, Graphics, Dialogs, ComCtrls;
9.  
10. type
11.  
12.   { TreeView }
13.  
14.   TreeView=class(ComCtrls.TTreeView)
15.     protected
16.       procedure Click; override;
17.   end;
18.  
19.   { TForm1 }
20.  
21.   TForm1 = class(TForm)
22.     procedure FormCreate(Sender: TObject);
23.   private
24.     TreeView : TTreeView;
25.   public
26.  
27.   end;
28.  
29. var
30.   Form1: TForm1;
31.  
32. implementation
33.  
34. {$R *.lfm}
35.  
36. { TreeView }
37.  
38. procedure TreeView.Click;
39. begin
40.   inherited;
41.   writeln('TreeView.Click');
42. end;
43.  
44. { TForm1 }
45.  
46. procedure TForm1.FormCreate(Sender: TObject);
47. var
48.   TreeNode : TTreeNode;
49. begin
50.   TreeView:=TTreeView.Create(self);
51.   TreeView.Parent:=self;
52.   TreeView.Align:=alClient;
53.   TreeNode:=TTreeNode.Create(TreeView.Items);
54.   TreeView.Items.Add(TreeNode,'ok1');
55.   TreeNode:=TTreeNode.Create(TreeView.Items);
56.   TreeView.Items.Add(TreeNode,'ok2');
57. end;
58.  
59. end.  

What is the reason for this different behavior? Thanks.

[jamie]

U never asigned the event so it's not going to be called. As for the button. U most likely used the OI to assign it.

[simsee]

No. In both cases controls are created at run-time, wiithout using object inspector at all.

I attached two compilable projects to reproduce.

[BrunoK]

Code: Pascal  [Select][+][-]

1. unit Unit1;
2.  
3. {$mode objfpc}{$H+}
4.  
5. interface
6.  
7. uses
8.   Classes, SysUtils, Forms, Controls, Graphics, Dialogs, ComCtrls;
9.  
10. type
11.  
12.   { TreeView }
13.  
14.   TMyTreeView=class(ComCtrls.TTreeView)
15.     protected
16.       procedure Click; override;
17.   end;
18.  
19.   { TForm1 }
20.  
21.   TForm1 = class(TForm)
22.     procedure FormCreate(Sender: TObject);
23.   private
24.     TreeView : TMyTreeView;
25.   public
26.  
27.   end;
28.  
29. var
30.   Form1: TForm1;
31.  
32. implementation
33.  
34. {$R *.lfm}
35.  
36. { TreeView }
37.  
38. procedure TMyTreeView.Click;
39. begin
40.   inherited;
41.   writeln('TreeView.Click');
42. end;
43.  
44. { TForm1 }
45.  
46. procedure TForm1.FormCreate(Sender: TObject);
47. var
48.   TreeNode: TTreeNode;
49. begin
50.   TreeView := TMyTreeView.Create(self);
51.   TreeView.Parent := self;
52.   TreeView.Align := alClient;
53.   TreeNode := TTreeNode.Create(TreeView.Items);
54.   TreeView.Items.Add(TreeNode, 'ok1');
55.   TreeNode := TTreeNode.Create(TreeView.Items);
56.   TreeView.Items.Add(TreeNode, 'ok2');
57. end;
58.  
59. end.

[simsee]

This was a simple typo: TreeType instead of TTreeType in line #14.

Code: Pascal  [Select][+][-]

1. unit Unit1;
2.  
3. {$mode objfpc}{$H+}
4.  
5. interface
6.  
7. uses
8.   Classes, SysUtils, Forms, Controls, Graphics, Dialogs, ComCtrls;
9.  
10. type
11.  
12.   { TreeView }
13.  
14.   TTreeView=class(ComCtrls.TTreeView)
15.     protected
16.       procedure Click; override;
17.   end;
18.  
19.   { TForm1 }
20.  
21.   TForm1 = class(TForm)
22.     procedure FormCreate(Sender: TObject);
23.   private
24.     TreeView : TTreeView;
25.   public
26.  
27.   end;
28.  
29. var
30.   Form1: TForm1;
31.  
32. implementation
33.  
34. {$R *.lfm}
35.  
36. { TreeView }
37.  
38. procedure TreeView.Click;
39. begin
40.   inherited;
41.   writeln('TreeView.Click');
42. end;
43.  
44. { TForm1 }
45.  
46. procedure TForm1.FormCreate(Sender: TObject);
47. var
48.   TreeNode : TTreeNode;
49. begin
50.   TreeView:=TTreeView.Create(self);
51.   TreeView.Parent:=self;
52.   TreeView.Align:=alClient;
53.   TreeNode:=TTreeNode.Create(TreeView.Items);
54.   TreeView.Items.Add(TreeNode,'ok1');
55.   TreeNode:=TTreeNode.Create(TreeView.Items);
56.   TreeView.Items.Add(TreeNode,'ok2');
57. end;
58.  
59. end.
60.  

You don't need to use a different type name in the derived class definition. Sorry.

[BrunoK]

This was a simple typo: TreeType instead of TTreeType in line #14.
You don't need to use a different type name in the derived class definition. Sorry.

Your code does not compile. Message

unit1.pas(38,11) Error: Identifier not found "TreeView"
unit1.pas(38,11) Error: class identifier expected
unit1.pas(40,12) Error: Methods can be only in other methods called direct with type identifier of the class

     

Correct to

Code: Pascal  [Select][+][-]

1. { TreeView }
2.  
3. procedure TTreeView.Click;
4. begin
5.   inherited;
6.   writeln('TreeView.Click');
7. end;

[simsee]

Yes, it is a consequence of the previous typo. I apologize.

[BrunoK]

It is not a good idea to 'façade' name an existing type with an identical class name. (except if you have a excellent reason to do it).

[simsee]

Yes, I agree, but the example comes from a refactoring context where I need an interceptor class for TTreeView. In this scenario, it makes sense.