IWMSDataContainerCallback::OnRead
.gif)
| Previous | Next |
IWMSDataContainerCallback::OnRead
The OnRead method returns the results of the IWMSDataContainer::Read method call.
Syntax
HRESULT OnRead( HRESULT hr, DWORD dwActualBytesTransferred, DWORD dwChangeType, QWORD qwChangeParameter, QWORD qwContext );
Parameters
hr
[in] HRESULT containing the result of the IWMSDataContainer::Read method call.
dwActualBytesTransferred
[in] DWORD containing the number of bytes of data transferred.
dwChangeType
[in] DWORD reserved for future use. Set this parameter to NULL.
qwChangeParameter
[in] QWORD reserved for future use. Set this parameter to NULL.
qwContext
[in] QWORD containing a value defined by the server to identify which IWMSDataContainer::Read request the plug-in is responding to when it calls OnRead. The plug-in must pass this value back unaltered.
Return Values
If the method succeeds, the plug-in must return S_OK. To report an error, the plug-in can return any HRESULT other than S_OK. If the plug-in uses the IWMSEventLog interface to log error information directly to the Windows Event Viewer, it is recommended that it return NS_E_PLUGIN_ERROR_REPORTED. Typically, the server attempts to make plug-in error information available to the server object model, the Windows Event Viewer, and the troubleshooting list in the details pane of the Windows Media Services MMC. However, if the plug-in uses the IWMSEventLog interface to send custom error information to the Windows Event Viewer, returning NS_E_PLUGIN_ERROR_REPORTED stops the server from also logging to the event viewer. For more information about retrieving plug-in error information, see Identifying Plug-in Errors.
Remarks
It is recommended that, if possible, your plug-in read at least one second of data before calling this method.
Example Code
The following example applies only to data contained in a file.
HRESULT STDMETHODCALLTYPE
CDataContainer::Read(
BYTE *pbBuffer,
QWORD qwReadPosition,
DWORD dwMaxDataSize,
IWMSDataContainerCallback *pCallback,
QWORD qwContext
)
{
HRESULT hr = S_OK;
BOOL fSuccess = FALSE;
// TODO: Allocate (not shown) and initialize an OVERLAPPED
// structure. The pOverLapped variable is a pointer to
// this structure. See the CreateFile() documentation in the
// MSDN library for more information.
// If you opened the container by using the
// FILE_FLAG_OVERLAPPED flag, an OVERLAPPED structure is
// required for a read operation.
pOverlapped->Offset = LODWORD( qwReadPosition );
pOverlapped ->OffsetHigh = ( LONG ) HIDWORD( qwReadPosition );
pOverlapped ->hEvent = NULL;
// Read the file.
fSuccess = ReadFile(
m_hFile,
pbBuffer,
dwMaxDataSize,
&m_dwBytesTransferred ),
( LPOVERLAPPED ) pOverLapped
);
// TODO: Specify HRESULT for read operation.
// Respond to the server.
hr = m_pCallback->OnRead(
hr,
m_dwBytesTransferred,
0,
0,
qwContext );
return( S_OK );
}
Requirements
Header: datacontainer.h.
Library: WMSServerTypeLib.dll.
Platform: Windows Server 2003, Enterprise Edition; Windows Server 2003, Datacenter Edition; Windows Server 2008.
See Also
| Previous | Next |