diff -r 43e37759235e -r 51a74ef9ed63 Symbian3/SDK/Source/GUID-1BD987D8-B018-51B7-80B2-4E1988841BC2.dita --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/Symbian3/SDK/Source/GUID-1BD987D8-B018-51B7-80B2-4E1988841BC2.dita Wed Mar 31 11:11:55 2010 +0100 @@ -0,0 +1,41 @@ + + + + + +How +to cancel requestsThis document describes how to cancel a previously scheduled request. +

The CActive class provides the Cancel() member +function to cancel an active object’s request.

+

If no request has been issued, Cancel() does nothing, +otherwise it calls DoCancel(). This is a pure virtual function +that must be provided by derived classes and which handles specific cancellation +as required by the service provider. Cancel() then waits +for the completion of that request and sets the active request flag to false.

+

The service provider must guarantee that the cancellation operation completes +in a very short period of time.

+

For example, a specialized timer active object, derived from CTimer which +is derived from CActive, might implement this as:

+void CTimedMessenger::DoCancel() + { + // Base class + CTimer::DoCancel(); + // Reset variable - needed if the object is later re-activated + iTicksDone = 0; + ... + } +

Note that an active object's destructor should ensure that any outstanding +requests are cancelled. If the class implements a DoCancel() function, then +the destructor must call the Cancel() member function. For +example:

+CTimedMessenger::~CTimedMessenger() + { + Cancel(); + } + \ No newline at end of file