Capturing keys in background - Forum Nokia Wiki

Capturing keys in background
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The CKeyCapturer implementation illustrates how to capture key events in a background process. Note that you need to define the key to be captured when using the CaptureKey() function (example is capturing the EKeyDevice0 key).

Also note that if the key should also be usable for the focused application, you need to manually forward it. This is already handled by the example as shown in the RunL() method. The callback interface function will return EFalse if the key is supposed to be forwarded to the focus application and ETrue if the key was consumed.

This example code should work with all platforms, but when used with S60 3rd Edition devices you need to have the SwEvent capability.

If you want to capture basic application keys in a foreground application you can use the standard OfferKeyEventL() method implemented in your CCoeControl derived class. If your application does not implement the standard application framework, you could also try using CKeyCapturer2 implementation.

[edit] CapturingKeys.cpp
CKeyCapturer* CKeyCapturer::NewL(MKeyCallBack& aObserver)
{
CKeyCapturer* self = CKeyCapturer::NewLC(aObserver);
CleanupStack::Pop(self);
return self;
}

CKeyCapturer* CKeyCapturer::NewLC(MKeyCallBack& aObserver)
{
CKeyCapturer* self = new (ELeave) CKeyCapturer(aObserver);
CleanupStack::PushL(self);
self->ConstructL();
return self;
}

CKeyCapturer::CKeyCapturer(MKeyCallBack& aObserver)
:CActive(EPriorityStandard),iObserver(aObserver),iHandle(-1)
{
}

CKeyCapturer::~CKeyCapturer()
{
if(iHandle > -1)
{
iWg.CancelCaptureKey(iHandle);
}

iHandle = -1;

Cancel();

iWg.Close();
iWsSession.Close();
}

void CKeyCapturer::ConstructL()
{
CActiveScheduler::Add(this);

User::LeaveIfError(iWsSession.Connect());

iWg=RWindowGroup(iWsSession);
User::LeaveIfError(iWg.Construct((TUint32)&iWg, EFalse));
iWg.SetOrdinalPosition(-1);
iWg.EnableReceiptOfFocus(EFalse);

CApaWindowGroupName* wn=CApaWindowGroupName::NewLC(iWsSession);
wn->SetHidden(ETrue);
wn->SetWindowGroupName(iWg);
CleanupStack::PopAndDestroy();

iHandle = iWg.CaptureKey(EKeyDevice0, 0,0);
Listen();
}

void CKeyCapturer::RunL()
{
if (iStatus == KErrNone)
{
TWsEvent e;
iWsSession.GetEvent(e);

if(iObserver.KeyCapturedL(e))
{
TInt wgId = iWsSession.GetFocusWindowGroup();
iWsSession.SendEventToWindowGroup(wgId, e);
}
}

if (iStatus != KErrCancel)
{
Listen();
}
}

void CKeyCapturer::DoCancel()
{
iWsSession.EventReadyCancel();
}

void CKeyCapturer::Listen()
{
iWsSession.EventReady(&iStatus);
SetActive();
}[edit] CapturingKeys.h
class MKeyCallBack
{
public:
virtual TBool KeyCapturedL(TWsEvent aEvent) = 0;
};

class CKeyCapturer : public CActive
{
public:
static CKeyCapturer* NewL(MKeyCallBack& aObserver);
static CKeyCapturer* NewLC(MKeyCallBack& aObserver);
virtual ~CKeyCapturer();
private:
CKeyCapturer(MKeyCallBack& aObserver);
void ConstructL();
void RunL();
void DoCancel();
void Listen();
private:
MKeyCallBack& iObserver;
RWsSession iWsSession;
RWindowGroup iWg;
TInt iHandle;
};