Component messaging

I defined my own windows message.  I have a handler procedure.  It works in the form, but not in the component.

The code is as follows:

const
  WM_VVTInterfaceMessage = 1125;

  protected
    procedure WMVVTInterfaceMessage(var Msg: TMessage); message WM_VVTInterfaceMessage;

Additionally, how can I pass a string in the message?
I tried using a PChar in the lParam, but I get GPFs and Delphi exits immediately.

Bryan
LVL 1
bcrotazAsked:
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JimBob091197Commented:
Hi Bryan

What component are you using as your base class?  (I.e. what are you inheriting from?)  I don't think TComponent has an HWND or a WndProc, so that may explain why your msg handler isn't working.

Also, what method are you currently using to pass a PChar?  How are you sending the message in lParam (PostMessage, SendMessage, Perform)?

JB
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d003303Commented:
Yo,
like JimBob said, you need a window handle and a window proc. Only descendants of TWinControl have these property/method.
If your message is received in the same process, i.e. the same application, you could typecast a PChar variable in the lParam using LongInt(PString) on the sender and PChar(lParam) on the receiver side.
If your message goes out of process boundaries you cannot transfer pointers, only the direct values of wParam and lParam. To get a string through in this scenario, it is getting tricky.

Slash/d003303
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JimBob091197Commented:
Hi doo3303

You are right about TWinControl having these, but you can use a work around.  Look at TThread in Classes.pas.  In particular, look at "AllocateWindow" which is a nested function inside the procedure "AddThread".

Cheers,
JB
0
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bcrotazAuthor Commented:
OK - I used TControl, so that explains that part.

How could I send a string between processes using a message?
0
bcrotazAuthor Commented:
I'm currently using PostMessage, cos I don't want the sender to wait for an answer.

I sent the PChar in the lParam by typecasting it to an longint.
0
JimBob091197Commented:
If you use PostMessage, you could have a problem.  With SendMessage you could solve your problem, because the calling procedure will then allocate AND free the string.

JB
0
d003303Commented:
Yo,
maybe you yould use the GetWindowText/SetWindowText API functions to work around these things. It also works across process boundaries. Note that this only works if the window text is not used for its standard purpose, like captioning.

Slash/d003303
0
ZifNabCommented:
To get messages to your component you need to make an invisible window :

 TCDEvents = class(TComponent)
  private
    { Private declarations }
     FWindowHandle: HWND;
     procedure WndProc(var Msg: TMessage);
  protected
    { Protected declarations }
  public
    { Public declarations }
     constructor Create(AOwner: TComponent); override;
     destructor Destroy; override;
  published
    { Published declarations }
  end;

constructor TCDEvents.Create(AOwner: TComponent);
begin
  inherited Create(AOwner);
  FWindowHandle := AllocateHWnd(WndProc);
end;

procedure TCDEvents.WndProc(var Msg: TMessage);
begin
 {handle the messages}
 if message then begin
 end
    else
      Msg.Result := DefWindowProc(FWindowHandle, Msg.Msg, Msg.wParam,         Msg.lParam);
end;

destructor TCDEvents.Destroy;
begin
  DeallocateHWnd(FWindowHandle);
  inherited Destroy;
end;

Regards, ZiF.


0
bcrotazAuthor Commented:
Hmmm... This isn't as simple as it could be.
Is there no way of allocating memory with global permissions, so every process can access it?
0
JimBob091197Commented:
Hi

You can create a global shared memory area using CreateFileMapping.  For an example of this, look for MY comments under the following (unanswered) question:
http://www.experts-exchange.com/topics/comp/lang/delphi/Q.10050013

Cheers,
JB
0
ZifNabCommented:
Not easy?  Not much code ....

It's the way delphi does it...

Regards, Zif.
0
ssiteCommented:
The right way to pass strings betweek apps is to use Atoms. Better yet, global atoms. Look it up in win32 help. It's pretty simple to do, but the string is limited to 255 chars.
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kjtengCommented:
There is a way to pass message to tControl: by calling the dispatch method eg  myControl.dispatch( userMessage);
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ssiteCommented:
Did you use control.perform ?

maybe 1125 is used as an internal mesage in the component. Try WM_MYMESSAGE = WM_USER + 100

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