CComCachedTearOffObject Class
This class implements IUnknown for a tear-off interface.
Syntax
template
<class contained>
class CComCachedTearOffObject : public
IUnknown,
public CComObjectRootEx<contained
::_ThreadModel::ThreadModelNoCS>
Parameters
contained
Your tear-off class, derived from CComTearOffObjectBase and the interfaces you want your tear-off object to support.
Members
Public Constructors
| Name | Description |
|---|---|
| CComCachedTearOffObject::CComCachedTearOffObject | The constructor. |
| CComCachedTearOffObject::~CComCachedTearOffObject | The destructor. |
Public Methods
| Name | Description |
|---|---|
| CComCachedTearOffObject::AddRef | Increments the reference count for a CComCachedTearOffObject object. |
| CComCachedTearOffObject::FinalConstruct | Calls the m_contained::FinalConstruct (the tear-off class' method). |
| CComCachedTearOffObject::FinalRelease | Calls the m_contained::FinalRelease (the tear-off class' method). |
| CComCachedTearOffObject::QueryInterface | Returns a pointer to the IUnknown of the CComCachedTearOffObject object, or to the requested interface on your tear-off class (the class contained). |
| CComCachedTearOffObject::Release | Decrements the reference count for a CComCachedTearOffObject object and destroys it if the reference count is 0. |
Public Data Members
| Name | Description |
|---|---|
| CComCachedTearOffObject::m_contained | A CComContainedObject object derived from your tear-off class (the class contained). |
Remarks
CComCachedTearOffObject implements IUnknown for a tear-off interface. This class differs from CComTearOffObject in that CComCachedTearOffObject has its own IUnknown, separate from the owner object's IUnknown (the owner is the object for which the tear-off is being created). CComCachedTearOffObject maintains its own reference count on its IUnknown and deletes itself once its reference count is zero. However, if you query for any of its tear-off interfaces, the reference count of the owner object's IUnknown will be incremented.
If the CComCachedTearOffObject object implementing the tear-off is already instantiated, and the tear-off interface is queried for again, the same CComCachedTearOffObject object is reused. In contrast, if a tear-off interface implemented by a CComTearOffObject is again queried for through the owner object, another CComTearOffObject will be instantiated.
The owner class must implement FinalRelease and call Release on the cached IUnknown for the CComCachedTearOffObject, which will decrement its reference count. This will cause CComCachedTearOffObject's FinalRelease to be called and delete the tear-off.
Inheritance Hierarchy
CComObjectRootBase
IUnknown
CComCachedTearOffObject
Requirements
Header: atlcom.h
CComCachedTearOffObject::AddRef
Increments the reference count of the CComCachedTearOffObject object by 1.
STDMETHOD_(ULONG, AddRef)();
Return Value
A value that may be useful for diagnostics and testing.
CComCachedTearOffObject::CComCachedTearOffObject
The constructor.
CComCachedTearOffObject(void* pv);
Parameters
pv
[in] Pointer to the IUnknown of the CComCachedTearOffObject.
Remarks
Initializes the CComContainedObject member, m_contained.
CComCachedTearOffObject::~CComCachedTearOffObject
The destructor.
~CComCachedTearOffObject();
Remarks
Frees all allocated resources and calls FinalRelease.
CComCachedTearOffObject::FinalConstruct
Calls m_contained::FinalConstruct to create m_contained, the CComContainedObject< contained> object used to access the interface implemented by your tear-off class.
HRESULT FinalConstruct();
Return Value
A standard HRESULT value.
CComCachedTearOffObject::FinalRelease
Calls m_contained::FinalRelease to free m_contained, the CComContainedObject< contained> object.
void FinalRelease();
CComCachedTearOffObject::m_contained
A CComContainedObject object derived from your tear-off class.
CcomContainedObject <contained> m_contained;
Parameters
contained
[in] Your tear-off class, derived from CComTearOffObjectBase and the interfaces you want your tear-off object to support.
Remarks
The methods m_contained inherits are used to access the tear-off interface in your tear-off class through the cached tear-off object's QueryInterface, FinalConstruct, and FinalRelease.
CComCachedTearOffObject::QueryInterface
Retrieves a pointer to the requested interface.
STDMETHOD(QueryInterface)(REFIID iid, void** ppvObject);
Parameters
iid
[in] The GUID of the interface being requested.
ppvObject
[out] A pointer to the interface pointer identified by iid, or NULL if the interface is not found.
Return Value
A standard HRESULT value.
Remarks
If the requested interface is IUnknown, returns a pointer to the CComCachedTearOffObject's own IUnknown and increments the reference count. Otherwise, queries for the interface on your tear-off class using the InternalQueryInterface method inherited from CComObjectRootEx.
CComCachedTearOffObject::Release
Decrements the reference count by 1 and, if the reference count is 0, deletes the CComCachedTearOffObject object.
STDMETHOD_(ULONG, Release)();
Return Value
In non-debug builds, always returns 0. In debug builds, returns a value that may be useful for diagnostics or testing.
See also
CComTearOffObject Class
CComObjectRootEx Class
Class Overview