[SOLVED]Control '' has no parent window

[CM630]

I am trying to handle Windows events in a custom control.
When I place the control on a form I get Control '' has no parent window.
If I comment (remove) the next line the error is not shown, but of course, events are not handled:
FPrevWndProc:=Windows.WNDPROC(SetWindowLongPtr(Self.Handle,GWL_WNDPROC,PtrUInt(@WndCallback)));
I suppose that is the form on which the control is located, which should handle the event, but I have to link it somehow.
Replacing Self.Handle with Parent.Handle causes some other error.

The exception is generated by Application.CreateForm(TForm1, Form1);   which is in the .LPR file of the sample app.

Code: Pascal  [Select][+][-]

1. unit ComboSample;
2.  
3. {$mode ObjFPC}{$H+}
4.  
5. interface
6.  
7. uses
8.   Classes, SysUtils, LResources, Forms, Controls, Graphics, Dialogs, StdCtrls,
9.   Windows;
10.  
11. type
12.   TComboSample = class(tcustomcombobox)
13.   private
14.     FPrevWndProc: Windows.WNDPROC;
15.     function WndCallback(Ahwnd: HWND; uMsg: UINT; wParam: WParam; lParam: LParam):LRESULT; stdcall;
16.   protected
17.  
18.   public
19.     constructor Create (aOwner: TComponent); override;
20.  
21.   published
22.  
23.   end;
24.  
25. procedure Register;
26.  
27. implementation
28.  
29. {$ifdef windows}
30. //Handles windows messages
31. function TComboSample.WndCallback(Ahwnd: HWND; uMsg: UINT; wParam: WParam; lParam: LParam):LRESULT; stdcall;
32. var
33.   mMessage : TMessage;
34. begin
35.   {if (uMsg = WM_DEVICECHANGE) then
36.   begin
37.     result:=Windows.DefWindowProc(Ahwnd, uMsg, WParam, LParam);  //not sure about this one
38.     mMessage.wParam:= wParam;
39.     mMessage.lParam:= lParam;
40.     mMessage.Result:= Result;
41.     WMPnPDeviceChange(mMessage);
42.     exit;
43.   end;
44.   result:=CallWindowProc(FPrevWndProc,Ahwnd, uMsg, WParam, LParam);}
45. end;
46. {$endif}
47.  
48. constructor TComboSample.Create (aOwner: TComponent);
49. begin
50.   inherited;
51.   FPrevWndProc:=Windows.WNDPROC(SetWindowLongPtr(Self.Handle,GWL_WNDPROC,PtrUInt(@WndCallback)));
52. end;
53.  
54.  
55. procedure Register;
56. begin
57.   RegisterComponents('MySample',[TComboSample]);
58. end;
59.  
60. end.

[LeP]

I don't think you can capture the handle during control creation, possibly during window creation.
But you don't need to; you can use 'inherited' to handle the original procedure without capturing it.

Code: Pascal  [Select][+][-]

1. type
2.   TMyCustomControl = class(tcustomcombobox)
3.     protected
4.       procedure CreateWnd; override;
5.       function WndProc(var Message: TMessage): Integer; override;
6.   end;
7.  
8. //Here you can do something
9. procedure TMyCustomControl.CreateWnd;
10. begin
11.   inherited CreateWnd;
12. end;
13.  
14. function TMyCustomControl.WndProc(var Message: TMessage): Integer;
15. begin
16.   case Message.Msg of
17.     WM_LBUTTONDOWN: //for example
18.       begin
19.         ShowMessage('Mouse Button Down!');
20.         Result := 0; // Messagge handled
21.       end;
22.     else
23.       Result := inherited WndProc(Message); // call original function
24.   end;
25.  

[CM630]

I don't think you can capture the handle during control creation, possibly during window creation.

Indeed, I should have taken care about that.

But you don't need to; you can use 'inherited' to handle the original procedure without capturing it.
...

There is some visibility isse.
combosample.pas(18,14) Error: There is no method in an ancestor class to be overridden: "WndProc(var TMessage):LongInt;"

WNDPROC is located in base.inc, but adding Base in the uses section does not compile.

Also, the event that I need to handle is WM_DEVICECHANGE, should it be handleable from the control itself?

[Thaddy]

WNDPROC is located in base.inc, but adding Base in the uses section does not compile.

You are not supposed to add inc files to a uses clause. They are not units.
They are part of a unit or program.

Also, WndProc is a method, it needs to be part of a TComponent or TForm. It is not standalone.
Look at the example that LeP gave you.

[LeP]

Also, the event that I need to handle is WM_DEVICECHANGE, should it be handleable from the control itself?

Yes: https://learn.microsoft.com/en-us/windows/win32/devio/wm-devicechange

Result TRUE to grant the request.

Result BROADCAST_QUERY_DENY to deny the request.

[Remy Lebeau]

I am trying to handle Windows events in a custom control.
When I place the control on a form I get Control '' has no parent window.

That is because you are trying to access Self.Handle in your constructor before a Parent has been assigned. A child control cannot create its HWND without a parent window.

I suppose that is the form on which the control is located, which should handle the event, but I have to link it somehow.

That is not necessary.  Any HWND can be registered via RegisterDeviceNotification() to receive WM_DEVICECHANGE messages.

In any case, you don't need to subclass the control's HWND directly. UI controls already handle that for you. Simply override the inherited WndProc() method instead. And you can override the inherited CreateWnd() method to know when your control's HWND is ready for use.

Try this instead:

Code: Pascal  [Select][+][-]

1. type
2.   TComboSample = class(TCustomComboBox)
3.   protected
4.     {$ifdef windows}
5.     FDevNotify: HDEVNOTIFY;
6.     procedure CreateWnd; override;
7.     procedure DestroyWnd; override;
8.     procedure WndProc(var Message: TMessage); override;
9.     {$endif}
10.   end;
11.  
12. {$ifdef windows}
13. procedure TComboSample.CreateWnd;
14. begin
15.   inherited;
16.   FDevNotify := RegisterDeviceNotification(Self.Handle, ...);
17. end;
18.  
19. procedure TComboSample.DestroyWnd;
20. begin
21.   if (FDevNotify <> 0) then
22.   begin
23.     UnregisterDeviceNotification(FDevNotify);
24.     FDevNotify := 0;
25.   end;
26.   inherited;
27. end;
28.  
29. procedure TComboSample.WndProc(var Message: TMessage);
30. begin
31.   inherited;
32.   if (Message.Msg = WM_DEVICECHANGE) then
33.     WMPnPDeviceChange(Message);
34. end;
35. {$endif}

[CM630]

...Try this instead...

So I added jwaWinUser in Uses.
Then I added

Code: Pascal  [Select][+][-]

1. const
2.   WM_DEVICECHANGE = $0219;
3.   DBT_DEVNODES_CHANGED = $0007;  

Then I changed

Code: Pascal  [Select][+][-]

1. procedure TComboSample.DestroyWnd;
2. begin
3.   if (FDevNotify <> 0) then
4.   begin
5.     UnregisterDeviceNotification(FDevNotify);
6.     FDevNotify := 0;

to

Code: Pascal  [Select][+][-]

1. procedure TComboSample.DestroyWnd;
2. begin
3.   if (FDevNotify <> nil) then
4.   begin
5.     UnregisterDeviceNotification(FDevNotify);
6.     FDevNotify := nil;

So

Code: Pascal  [Select][+][-]

1. procedure TComboSample.CreateWnd;
2. begin
3.   inherited;
4.   FDevNotify := RegisterDeviceNotification(Self.Handle, @Hello,WM_DEVICECHANGE);
5. end;  

does not run, again Control '' has no parent window on inherited;.

I removed inherited;, but I get stack overflow.


Here is what I got:

Code: Pascal  [Select][+][-]

1. unit CustomComboBox;
2.  
3. {$mode ObjFPC}{$H+}
4.  
5. interface
6.  
7. uses
8.   Classes, SysUtils, LResources, Forms, Controls, Graphics, Dialogs, StdCtrls,
9.   Windows, jwaWinUser, messages;
10.  
11. type
12.   TComboSample = class(tCustomComboBox)
13.   private
14.     fPnP_DevNodeChange : boolean;
15.     fPnP_Removal : boolean;
16.     fTestProperty: boolean;
17.   protected
18.     {$ifdef windows}
19.     FDevNotify: HDEVNOTIFY;
20.     procedure CreateWnd; override;
21.     procedure DestroyWnd; override;
22.     procedure WndProc(var Message: TMessage); override;
23.     procedure WMPnPDeviceChange(var Message: TMessage);
24.     {$endif}
25.   public
26.     constructor Create (aOwner: TComponent); override;
27.   published
28.     property TestProperty: boolean read fTestProperty write fTestProperty ;
29.  
30.   end;
31.  
32. const
33.   WM_DEVICECHANGE = $0219;
34.   DBT_DEVNODES_CHANGED = $0007;
35.  
36. procedure Register;
37.  
38. implementation
39.  
40.  
41. procedure Hello;
42. begin
43.   ShowMessage ('hello');
44. end;
45.  
46. {$ifdef windows}
47. procedure TComboSample.CreateWnd;
48. begin
49. //  inherited;
50.   FDevNotify := RegisterDeviceNotification(Self.Handle, @Hello,WM_DEVICECHANGE);
51. end;
52.  
53. procedure TComboSample.DestroyWnd;
54. begin
55.   if (FDevNotify <> nil) then
56.   begin
57.     UnregisterDeviceNotification(FDevNotify);
58.     FDevNotify := nil;
59.   end;
60.   inherited;
61. end;
62.  
63. procedure TComboSample.WMPnPDeviceChange(var Message: TMessage);
64. begin
65.   if (Message.WParam = DBT_DEVNODES_CHANGED) then
66.   begin
67.     fPnP_DevNodeChange := true;
68.     fPnP_Removal := false;
69.   end;
70. end;
71.  
72. procedure TComboSample.WndProc(var Message: TMessage);
73. begin
74.   inherited;
75.   if (Message.Msg = WM_DEVICECHANGE) then
76.     WMPnPDeviceChange(Message);
77. end;
78. {$endif}
79.  
80. constructor TComboSample.Create (aOwner: TComponent);
81. begin
82.   inherited;
83.   {if HasParent then }CreateWnd;
84.   ShowMessage ('Created');
85. end;
86.  
87. procedure Register;
88. begin
89.   RegisterComponents('Additional',[TComboSample]);
90. end;
91.  
92. end.

Still, why the HEX the control is created before its parent 

compile.
You are not supposed to add inc files to a uses clause. They are not units.
They are part of a unit or program.
...

Still override; does not compile.

[jamie]

Hmm
Although I never thought of registering the window but try this in any case.
Try this.

[CM630]

Thanks, your sample app mostly works (for example, on connecting/disconnecting my camera, all I get is Msg.wParam = 7, not a problem, anyway), at least it detects when a device is attached/detached with some small modification.
But still, I could not make it work in a component.
I added msghook.pas to the package.
But when I did:

Code: Pascal  [Select][+][-]

1. constructor TComboSample.Create (aOwner: TComponent);
2. begin
3.   inherited;
4.   {You have a choice, Single inputs or array input }
5.   AddMsg(Self, WM_DeviceChange);
6.   AddMsg(Self,WM_SIZING);
7.   AddMsg(Self, WM_MOVING);
8.   { or Just this one line that defaults to afmNone for Exit action}
9.   AddMsgs(Self,[WM_DEVICECHANGE,WM_SIZING,WM_MOVING]);
10.   {Messages won't duplicate}
11. end;    

I got Error: Incompatible type for arg no. 1: Got "TComboSample", expected "TCustomForm"

The definition is Function AddMsg(Aform:TCustomForm; AMSg:UINT;AReturnType:TAfmDefaultAction=afmNone):Boolean;, but I have no form (yet).
Changing Aform:TCustomForm; to Aform:TComponent; did not help, it resulted in
Function AddMsg(Aform: in all cases of Aform.Handle.

[Thaddy]

Please, go back to the first answer by LeP, try to understand that and only THEN complain again....
You've already got the answer.

[CM630]

Going back to the first post by @LeP:
1.     function WndProc(var Message: TMessage): Integer; override;
Override does not compile, possibly because the routine to be overridden is a procedure, not a function.
2. After removing the override; from the code:
Result := inherited WndProc(Message); // call original function does not compile.

Error: Invalid assignment, procedures return no value

Possibly because trying to assign a procedure to an integer.


Edit: There is some progress, this handles mouse clicks, but it does not react on connecting/ disconnecting devices:

Code: Pascal  [Select][+][-]

1. unit ComboSample;
2.  
3. {$mode ObjFPC}{$H+}
4.  
5. interface
6.  
7. uses
8.   Windows, Classes, SysUtils, LResources, Forms, Controls, Graphics, Dialogs, StdCtrls,
9.    Lcl, msghook;
10.  
11. type
12.   TComboSample = class(tcustomcombobox)
13.   protected
14.     procedure CreateWnd; override;
15.     procedure WndProc(var Message: TMessage); override;
16.   public
17.     constructor Create (aOwner: TComponent); override;
18.   published
19.  
20.   end;
21.  
22. procedure Register;
23.  
24. implementation
25.  
26. constructor TComboSample.Create (aOwner: TComponent);
27. begin
28.   inherited;
29.   //CreateWnd;
30. end;
31.  
32. procedure TComboSample.CreateWnd;
33. begin
34.   inherited CreateWnd;
35. end;
36.  
37. procedure TComboSample.WndProc(var Message: TMessage);
38. begin
39.   writeln (IntToStr(Message.Msg));
40.   case Message.Msg of
41.     WM_LBUTTONDOWN: begin ShowMessage('Mouse Button Down!'); parent.Caption := 'WM_LBUTTONDOWN'; end;
42.     WM_DEVICECHANGE : ShowMessage('WM_DEVICECHANGE');
43.   else
44.       inherited WndProc(Message); // call original function
45.   end;
46. end;    
47.  
48. procedure Register;
49. begin
50.   RegisterComponents('MySample',[TComboSample]);
51. end;
52.  
53. end.
54.  

[LeP]

Going back to the first post by @LeP:
1.     function WndProc(var Message: TMessage): Integer; override;
Override does not compile, possibly because the routine to be overridden is a procedure, not a function.
2. After removing the override; from the code:
Result := inherited WndProc(Message); // call original function does not compile.

Error: Invalid assignment, procedures return no value

Possibly because trying to assign a procedure to an integer.

Yes, the firms of that method is different, it's a procedure not a function.

I think that this should be the good version:

Code: Pascal  [Select][+][-]

1. type
2.   TMyCustomControl = class(tcustomcombobox)
3.     protected
4.       procedure CreateWnd; override;
5.       procedure WndProc(var Message: TMessage); override;
6.   end;
7.  
8. //Here you can do something
9. procedure TMyCustomControl.CreateWnd;
10. begin
11.   inherited CreateWnd;
12. end;
13.  
14. //EDIT: pairing with definition
15.  
16. procedure TMyCustomControl.WndProc(var Message: TMessage);
17. begin
18.   case Message.Msg of
19.     WM_DEVICECHANGE: //for example
20.       begin
21.         writeln('DEVICE Change message: ', Message.wparam);
22.         Message.Result := 0; // Messagge handled.
23.       end;
24.     else
25.       inherited WndProc(Message); // call original function
26.   end;
27. end;

It's not necessary to regsiter the notify. But if you want to do you don't have to act like you do, those are the step (forget the previous):

I have not tested them, only catch and adapt form very old code.

Code: Pascal  [Select][+][-]

1. type
2. TMyCustomControl = class(tcustomcombobox)
3.     private
4.        procedure InitResources_1;
5.        procedure InitResources_2;
6.     protected
7.       procedure CreateWnd; override;
8.       procedure WndProcNew(var Message: TMessage);
9.    public
10.      destructor; Destroy; override;
11.   end;
12.  
13. const
14.  DBT_DEVTYP_DEVICEINTERFACE = $5;
15.  DEVICE_NOTIFY_WINDOW_HANDLE = $0;
16.  DEVICE_NOTIFY_ALL_INTERFACE_CLASSES = $4;
17.  //THIS IS A GUI FOR USB
18.  GUID_DEVINTERFACE_USB_DEVICE: TGUID = '{A5DCBF10-6530-11D2-901F-00C04FB951ED}';
19.  
20. type
21.   DEV_BROADCAST_HDR_DEVICE_TYPE = Cardinal;
22.   DEV_BROADCAST_HDR = record
23.     dbch_size: Cardinal;
24.     dbch_devicetype: DEV_BROADCAST_HDR_DEVICE_TYPE;
25.     dbch_reserved: Cardinal;
26.   end;
27.  
28. type
29.   DEV_BROADCAST_DEVICEINTERFACE_W = record
30.     dbcc_size: Cardinal;
31.     dbcc_devicetype: Cardinal;
32.     dbcc_reserved: Cardinal;
33.     dbcc_classguid: TGuid;
34.     dbcc_name: array[0..0] of AnsiChar;
35.   end;
36.  
37. var _dev: Dev_Broadcast_DeviceInterface_W;
38.  
39. var DevBlockRem: DEV_BROADCAST_HDR;
40.     FDevNotify: HDEVNOTIFY;
41.     NewHandle: HWND;
42.  
43.  
44. procedure TMyCustomControl.CreateWnd;
45. begin
46.   inherited CreateWnd;
47.   //These two calls are equivalent like the have constructed here
48.   //USE ONLY ONE OF THEM !!!
49.   //Call this if you want define some type of resources, see documentation
50.   InitResources_1;
51.   //Call this if you want define Hardware resources
52.   //InitResources_2;
53. end;
54.  
55. procedure TMyCustomControl.InitResources_1;
56. begin
57.   NewHandle:=AllocateHwnd(WndProcNew);
58.   ZeroMemory(@_dev, sizeOf(Dev_Broadcast_DeviceInterface_W));
59.   with _dev do
60.     begin
61.       dbcc_size:=sizeOf(Dev_Broadcast_DeviceInterface_W);
62.       dbcc_devicetype:= DBT_DEVTYP_DEVICEINTERFACE;
63.       dbcc_reserved:=0;
64.       dbcc_classguid:= GUID_DEVINTERFACE_USB_DEVICE;
65.       dbcc_name:=chr(0);
66.     end;
67.   //Use "DEVICE_NOTIFY_ALL_INTERFACE_CLASSES" if you want catch all messages from all classes (ignore dbcc_classguid)
68.   FDevNotify:=RegisterDeviceNotification(NewHandle, @_dev, DEVICE_NOTIFY_WINDOW_HANDLE or DEVICE_NOTIFY_ALL_INTERFACE_CLASSES);
69.   Win32Check(FDevNotify <> nil);
70. end;
71.  
72. procedure TMyCustomControl.InitResources_2;
73. begin
74.   NewHandle := AllocateHWnd(WndProcNew);
75.   ZeroMemory(@DevBlockRem, sizeOf(DevBlockRem));
76.   DevBlockRem.dbch_size := sizeof(DEV_BROADCAST_HDR)+sizeof(DEV_BROADCAST_DEVICEINTERFACE_W);
77.   DevBlockRem.dbch_devicetype := DBT_DEVTYP_DEVICEINTERFACE;
78.   DevBlockRem.dbch_reserved := 0;
79.   FDevNotify := nil;
80.   FDevNotify :=  RegisterDeviceNotification(NewHandle, @DevBlockRem, DEVICE_NOTIFY_WINDOW_HANDLE or DEVICE_NOTIFY_ALL_INTERFACE_CLASSES);
81.   Win32Check(FDevNotify <> nil);
82. end;
83.  
84. destructor TMyCustomControl.Destroy;
85. begin
86.   if FDevNotify <> nil then
87.     UnregisterDeviceNotification(FDevNotify);
88.  
89.   inherited;
90. end;
91.  
92. procedure TMyCustomControl.WndProcNew(var Message: TMessage);
93. begin
94.   case Message.Msg of
95.     WM_DEVICECHANGE: //for example
96.       begin
97.         writeln(Message.WParam);
98.         //Message.Result := 0; // Messagge handled
99.       end;
100.   end;
101. end;
102.  

[LeP]

Please, go back to the first answer by LeP, try to understand that and only THEN complain again....
You've already got the answer.

Sorry @Thaddy but I was wrong with WndProc, It's been a long time since I used this mode to "capture" Windows messages (probably back in the Windows XP days).

[CM630]

Thanks, I suppose you have not seen the edit of my previous post.
I think the first snippet from your post will not compile, one definition of WndProc is a procedure, but still, the other one is a function.

If you take a look at my previous post:

Code: Pascal  [Select][+][-]

1. ...
2. procedure TComboSample.WndProc(var Message: TMessage);
3. begin
4.   writeln (IntToStr(Message.Msg));
5.   case Message.Msg of
6.     WM_LBUTTONDOWN: begin ShowMessage('Mouse Button Down!'); parent.Caption := 'WM_LBUTTONDOWN'; end;
7.     WM_DEVICECHANGE : ShowMessage('WM_DEVICECHANGE');
8.   else
9.       inherited WndProc(Message); // call original function
10.   end;
11. end;  
12. ...  

There is output from  writeln (IntToStr(Message.Msg)); only when I am doing something with the control (mouse, keyboard...)
Nothing happens when I unplug and replug devices in the PC.


I have not looked at the second snippet in your last post, yet.

EDIT:
I tried it,  NewHandle:=AllocateHwnd(WndProcNew);   does not compile (Error: Wrong number of parameters specified for call to "WndProcNew").

[LeP]

@CM630, in the first example the implementation was wrong of course should be pair with declaration ... I modified it.

This time I tried it, with Lazarus and Delphi, and while in Delphi the messages are present, in Lazaru not.
I tried also with FORM1 (instead of MyCustom...).

Now I will try with the second sample.