WM_INPUT (RawData) to *Selectively* Intercept Keyboard Input?

[DavidM]

I am working on an application that needs to intercept keystrokes from a specific keyboard device without affecting the standard "legacy" messages from other keyboard devices. I have successfully implemented the RegisterRawInputDevices() function, and I can receive and read the WM_INPUT message and data. By checking the device handle in the RAWINPUTHEADER, I can determine which keystrokes are from the device of interest. I can then send an application message indicating the action to be taken. However, when the keystroke comes from some other keyboard device, i.e. the standard keyboard, I really just want to let the system handle the keystroke normally.

If I register the devices with the RIDEV_NOLEGACY flag, then none of these messages (WM_KEYDOWN, WM_KEYUP, etc) is sent by the system for any of the keyboard devices. If I do not use the RIDEV_NOLEGACY flag, then these messages are sent for all keyboard devices, including the one I want to intercept. Is there any way to suppress the "legacy" messages for the keystrokes I intercept, or to force the legacy messages for the keystrokes I don't?

I would welcome comments or suggestions from anyone who has used this process, especially in a Delphi application. I am developing on Windows XP Professional (SP1) using Delphi 2005.

[DavidM]

Quote: Text Previous Post
I am working on an application that needs to intercept keystrokes from a specific keyboard device without affecting the standard "legacy" messages from other keyboard devices. ...

Just in case anyone is interested, I solved this problem myself, although I think it is a hack. When I register for the raw input, I did NOT use the RIDEV_NOLEGACY flag, so all messages are sent. Then assigned the following function to the Application.OnMessage property:

[DELPHI]procedure TRawObj.AppMsgHandler (var Msg: TMsg; var Handled: Boolean);
begin
Handled := False;
if ((hSendMsg <> 0) and ((oDevList.Count > 0) or (bScanning))) then
begin
case Msg.message of
WM_INPUT: Handled := AppMsg_WMINPUT(Msg);
WM_KEYFIRST..WM_KEYLAST: Handled := bSkipLegacy;
end;
end;
end;
[/DELPHI]
Note that bSkipLegacy is a private property of the TRawObj class. It is set to True in the AppMsg_WMINPUT funtion if the message came from my device. If Handled is set to true, then the message will not be handled by the default processing.

The AppMsg_WMINPUT function is rather long, so I will not post it here, but if anyone is interested, I will be glad to provide the source. In essence the function:
1) uses GetRawData to retrieve the HEADER and DATA;
2) if the HEADER.hDevice is NOT my device:
then Set bSkipLegacy = False; and return false;
else Set bSkipLegacy = True; PostMessage to my form; return true;



Talking to yourself is OK, unless you start answering your own questions. ... Hmm ...

[7gsoft]

Many thanks for this tip, handling WM_INPUT (that doesn't accept obviously a result) then giving it's handled state to WM_Keydown and others to block messages that we don't want farther in the application is exactly what i've been searching for for nearly 4 days !!

i used your trick to handle a keypad for secure identification; it was declared in windows peripherals as a Keyboard, so intercepting its messages with rawinput and WM_INPUT was quite easy, but avoiding its WM_KEYDOWN message from displaying the identifier was my main problem.

many thanks again !

[usear]

Hello all,

I am really interested in using the wm_input api and have a slightly different application for it.

If any of you can share the source for your implementation I will be grateful.

Basically I have an application with multiple touch screens and I want to identify which touch screen the input is comming from do decide whether to use or ignore the input.

Kind Regards

Umar

[talexone]

Hello,
I use usb rfid reader as hid keyboard device. I put together a pieces of DavidM code I found on this site and it works well just for one instance, others apps still get input from both keyboards.

Tried with SetWindowsHookEx, but can't get deviceid with it.

DavidM: Your solution can solve it, or you just use one app?

Regards,
Alex