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7.8

How to write a callback method in delphi dll to a delphi client app

Asked by ddideveloper in Delphi Components, Delphi Programming

Tags: delphi dll callback method

I am trying to write a delphi dll and a delphi client that will load the dll and have the dll call a method in the client. so far i have my client and dll are able to share data via a memory map without any problems. Now I want to write a method in the client that gets called by the dll if a certain event occurs.
I added a variable to my memory map structure to hold a pointer to the client method. The dll then checks to see if that variable is Assigned() then it calls it passing some variables. This is actually working so long as my client application never loses focus. If I ever click on another application, say windows explorer or something, then the dll stops working all together. By not working it does not appear to update the memory map or call the callback method either.
By the way I am using Delphi 7 and running on Windows XP.

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             code snippet from dll
------------
type
  TKeyboardEvent = procedure(Code: integer; wParam: integer; lParam: integer); stdcall ;
 
 PHookRec = ^THookRec;
 THookRec = packed record
   KeyboardEvent      : TKeyboardEvent ;
   TheHookHandle      : HHOOK;
   TheAppWinHandle    : HWND;
   TheCtrlWinHandle   : HWND;
   TheKeyCount        : DWORD;
   KeyChar            : Char ;
 end;
 
....
in one of the methods in dll i have thie following lines of code
 
 if Assigned(lpHookRec^.KeyboardEvent) then
  TKeyboardEvent(lpHookRec^.KeyboardEvent)(Code, wParam, lParam) ;
 
-------------------------------
code snippets from client
------------------------------
type
  TKeyboardEvent = procedure(Code: integer; wParam: integer; lParam: integer); stdcall ;
 
<more code here>
 
  procedure KeyboardEvent(Code: integer; wParam: integer; lParam: integer); stdcall ;
 
implementation
 
{$R *.DFM}
 
// The record type filled in by the dll
type THookRec = packed record
  KeyboardEvent     : TKeyboardEvent ;
  TheHookHandle     : HHOOK;
  TheAppWinHandle   : HWND;
  TheCtrlWinHandle  : HWND;
  TheKeyCount       : DWORD;
  KeyChar           : Char ;
end;
type PHookRec = ^THookRec;
 
<in my client after the dll is loaded and memory map established...>
         lpHookRec^.KeyboardEvent := @KeyboardEvent ;

           
         

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How to write a callback method in delphi dll to a delphi client app

Asked by ddideveloper in Delphi Components, Delphi Programming

Tags: delphi dll callback method

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