From Forum Nokia Wiki

The code below shows how a thread can capture some keys and react to them, optionally sending them to the top app if it's not interested in them itself. You'll only need a cleanup stack active for this thread, no active scheduler needed.

Headers Required:

#include <W32STD.H> 
#include <APGWGNAM.H>
#include <e32keys.h> //for key codes

Libraries Required:

LIBRARY  ws32.lib
LIBRARY apgrfx.lib

Source:

// connect to window server
	RWsSession ws;
	User::LeaveIfError(ws.Connect());
	CleanupClosePushL(ws);
 
	TRequestStatus status;
 
	// create a window group for the thread
	RWindowGroup wg(ws);
	wg.Construct((TUint32)&wg, EFalse);
	CleanupClosePushL(wg);
 
	// capture a key
	User::LeaveIfError(wg.CaptureKey(EKeyLeftArrow, 0, 0));
 
	// listen for the key presses
	ws.EventReady(&status);
 
	// hide this window group from the app switcher
	wg.SetOrdinalPosition(-1);
	wg.EnableReceiptOfFocus(EFalse);
	CApaWindowGroupName* wn=CApaWindowGroupName::NewLC(ws);
	wn->SetHidden(ETrue);
	wn->SetWindowGroupName(wg);
 
	// handle key events
	for(;;) {
		User::WaitForAnyRequest();
		if (status.Int()==KErrNone) {
			TWsEvent e;
			ws.GetEvent(e);
 
			TInt c;
			TKeyEvent* aKeyEvent=e.Key();
			c=aKeyEvent->iCode;
 
			// do something with keypress
 
			// if not ours, then send to top window group			
			// note that this breaks key repeat 
         		TInt wgid=ws.GetFocusWindowGroup();
			ws.SendEventToWindowGroup(wgid, e);
		}
		ws.EventReady(&status);
 
		// stop condition
	}
 
	// clean up
	ws.EventReadyCancel();
	CleanupStack::PopAndDestroy(3); //ws, wg, wn

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