IMMDeviceEnumerator::RegisterEndpointNotificationCallback method (mmdeviceapi.h)

Article
02/22/2024

The RegisterEndpointNotificationCallback method registers a client's notification callback interface.

Syntax

HRESULT RegisterEndpointNotificationCallback(
  [in] IMMNotificationClient *pClient
);

Parameters

[in] pClient

Pointer to the IMMNotificationClient interface that the client is registering for notification callbacks.

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 code	Description
E_POINTER	Parameter pNotify is NULL.
E_OUTOFMEMORY	Out of memory.

Remarks

This method registers an IMMNotificationClient interface to be called by the system when the roles, state, existence, or properties of an endpoint device change. The caller implements the IMMNotificationClient interface.

When notifications are no longer needed, the client can call the IMMDeviceEnumerator::UnregisterEndpointNotificationCallback method to terminate the notifications.

The client must ensure that the IMMNotificationClient object is not released after the RegisterEndpointNotificationCallback call and before calling UnregisterEndpointNotificationCallback. These methods do not call the client's IMMNotificationClient::AddRef and IMMNotificationClient::Release implementations. The client is responsible for maintaining the reference count of the IMMNotificationClient object. The client must increment the count if the RegisterEndpointNotificationCallback call succeeds and release the final reference only after calling UnregisterEndpointNotificationCallback or implement some other mechanism to ensure that the object is not deleted before UnregisterEndpointNotificationCallback is called. Otherwise, the application leaks the resources held by the IMMNotificationClient and any other object that is implemented in the same container.

For more information about the AddRef and Release methods, see the discussion of the IUnknown interface in the Windows SDK documentation.

Requirements

Requirement	Value
Minimum supported client	Windows Vista [desktop apps only]
Minimum supported server	Windows Server 2008 [desktop apps only]
Target Platform	Windows
Header	mmdeviceapi.h