ArcGIS Engine Developer Guide

VISUAL C++
// Create dialog class on the heap using ATL CComObject template.
CComObject *myDlg;
CComObject::CreateInstance(&myDlg);
myDlg->AddRef(); // Keep dialog box alive until you're done with it.
myDlg->DoModal(); // Launch the dialog box; when method returns, dialog
box has exited.
myDlg->Release(); // Typically, the refcount now goes to 0 and frees the
dialog object.
• Implement an intermediate COM object for use by the sink; this is sometimes
called a listener or event helper object. This object typically contains no implementation
but simply uses C++ method calls to forward events to the sink
object. The listener has its reference count incremented by the source, but the
sink’s reference count is unaffected. This breaks the cycle, allowing the sink’s
reference count to reach 0 when all other references are released. As the sink
executes its destructor code, it instructs the listener to unadvise and release
the source.
An alternative to using C++ pointers to communicate between listener and sink
is to use an interface pointer that is a weak reference. That is, the listener contains
a COM pointer to the sink but does not increment the sink’s reference
count. It is the responsibility of the sink to ensure that this pointer is not accessed
after the sink object has been released.
140 • ArcGIS Engine Developer Guide