IPart::RegisterControlChangeCallback method

The RegisterControlChangeCallback method registers the IControlChangeNotify interface, which the client implements to receive notifications of status changes in this part.


HRESULT RegisterControlChangeCallback(
  [in] REFGUID              riid,
  [in] IControlChangeNotify *pNotify


riid [in]

The function-specific control interface that is to be monitored for control changes. For more information, see Remarks.

pNotify [in]

Pointer to the client's IControlChangeNotify interface. If the method succeeds, it calls the AddRef method on the client's IControlChangeNotify interface.

Return value

If the method succeeds, it returns S_OK. If it fails, possible return codes include, but are not limited to, the values shown in the following table.

Return codeDescription

Parameter riid is not a valid control-interface identifier.


Pointer pNotify is NULL.



Set parameter riid to one of the following GUID values:

  • IID_IAudioAutoGainControl
  • IID_IAudioBass
  • IID_IAudioChannelConfig
  • IID_IAudioInputSelector
  • IID_IAudioLoudness
  • IID_IAudioMidrange
  • IID_IAudioMute
  • IID_IAudioOutputSelector
  • IID_IAudioPeakMeter
  • IID_IAudioTreble
  • IID_IAudioVolumeLevel
  • IID_IDeviceSpecificProperty
  • IID_IKsFormatSupport
  • IID_IKsJackDescription

To obtain the interface ID of the function-specific control interface for a part, call the part's IControlInterface::GetIID method. To obtain the interface ID of a function-specific control interface type, use the __uuidof operator. For example, the interface ID of IAudioAutoGainControl is defined as follows:

const IID IID_IAudioAutoGainControl  __uuidof(IAudioAutoGainControl)

For more information about the __uuidof operator, see the Windows SDK documentation.

Before the client releases its final reference to the IControlChangeNotify interface, it should call the IPart::UnregisterControlChangeCallback method to unregister the interface. Otherwise, the application leaks the resources held by the IControlChangeNotify and IPart objects. Note that RegisterControlChangeCallback calls the client's IControlChangeNotify::AddRef method, and UnregisterControlChangeCallback calls the IControlChangeNotify::Release method. If the client errs by releasing its reference to the IControlChangeNotify interface before calling UnregisterControlChangeCallback, the IPart object never releases its reference to the IControlChangeNotify interface. For example, a poorly designed IControlChangeNotify implementation might call UnregisterControlChangeCallback from the destructor for the IControlChangeNotify object. In this case, the client will not call UnregisterControlChangeCallback until the IPart object releases its reference to the IControlChangeNotify interface, and the IPart object will not release its reference to the IControlChangeNotify interface until the client calls UnregisterControlChangeCallback. For more information about the AddRef and Release methods, see the discussion of the IUnknown interface in the Windows SDK documentation.


Minimum supported client

Windows Vista [desktop apps only]

Minimum supported server

Windows Server 2008 [desktop apps only]



See also

IControlChangeNotify Interface
IPart Interface