>>>>Is there a way to trap the a WM_USER message sent to the main foxpro window?
>>>
>>>Albert,
>>>
>>>There's no way to "trap" (as you would with a keystroke), but setting a timer up to call the PeekMessage API function will allow you to simulate this behavior.
>>>
>>>
>>>hth,
>>>
>>>George
>>
>>Thanks,
>>
>>What about hooking the system messages with SetWindowsHookEx()?
>>
>>The following is a skelleton of what I am considering:
>>
>>HHOOK SetWindowsHookEx(
>>
>> int idHook, // type of hook to install
>> HOOKPROC hkprc, // address of hook procedure
>> HINSTANCE hMod, // handle of application instance
>> DWORD dwThreadID // identity of thread to install hook for
>> );
>>
>>typedef struct tagCWPSTRUCT { // cwps
>>
>> // Specifies additional information about the message.
>> // The exact meaning depends on the message value.
>> LPARAM lParam;
>> // Specifies additional information about the message.
>> // The exact meaning depends on the message value.
>> WPARAM wParam;
>> // Specifies the message.
>> UINT message;
>> // Identifies the window to receive the message.
>> HWND hwnd;
>>} CWPSTRUCT;
>>
>>myHook(WH_CALLWNDPROC, &myCallback, VFP_HInstance, VFP_ThreadID);
>>
>>// VFP_HInstance, VFP_ThreadID : How do I get these?
>>
>>LRESULT CALLBACK myCallback(
>>
>> int nCode, // hook code
>> WPARAM wParam, // current-process flag
>> LPARAM lParam // address of structure with message data
>> )
>>{
>> if (lParam->message == MESSAGE_TO_TRAP && lParam->hwnd == VFP_hwnd)
>> {
>> PASS MESSAGE BACK TO FOXPRO CODE
>> }
>>
>> if (nCode == HC_Action)
>> {
>> PROCESS THE MESSAGE
>> }
>>
>> return (nCode < 0) ? CallNextHookEx(), 0;
>>}
>
>Albert,
>
>I'll plead ignorance about this. I'm not sure that you can implement a hook without using native code. Further, I think I remember from somewhere that you can't access callbacks from VFP. I could very well be wrong about either or both of these. Maybe someone else can clarify this for you.
>
>Without knowing exactly what you're trying to do here, it's a little tough for me to comment further. However, enabling FoxPro's DDE features could serve the same purpose without running into the biggest potential problem associated with hooks: system performance degradation.
>
>hth,
>
>George

I would write an .FLL and interface through the VFP API. The callback would be written in C.

The code in the callback would be minimal, but there would still be call and processing overhead. I am planning to use DDE for this application, but I may be forced to use this technique in the future when I don't have a say. Another plus for DDE is the option of NetDDE. DDE is slow for transfering large blocks of data and you often have to parse the data block, but all I need is a connection to notify my App of the message. The reason I began investigating the Windows message communication is because it is currently implemented for a set of C++ Apps whith which the VFP Apps work.