Windows Media Player 11 SDK Handling Events in C++ 

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Handling Events in C++

You can receive events from Windows Media Player in two ways.

• Through IDispatch by using the _WMPOCXEvents interface. This is the interface to use for most embedding scenarios.
• Through the IWMPEvents interface. This interface is available when your code is connected to the full mode Player, such as when remoting the Windows Media Player control or in a UI plug-in.

In each scenario, you start listening to events by using COM connection points.

The following example code uses three member variables:

CComPtr<IWMPPlayer>         m_spWMPPlayer;
CComPtr<IConnectionPoint>   m_spConnectionPoint;
DWORD                       m_dwAdviseCookie;

To retrieve a connection point, you first QueryInterface for the connection point container.

HRESULT  hr = S_OK;
// Smart pointer to IConnectionPointContainer
CComPtr<IConnectionPointContainer>  spConnectionContainer;

hr = m_spWMPPlayer->QueryInterface(&spConnectionContainer);

Next, request the connection point for the event interface you want to use. The following example code first attempts to use IWMPEvents. If that interface isn't available, it uses _WMPOCXEvents.

// Test whether the control supports the IWMPEvents interface.
if(SUCCEEDED(hr))
{
    hr = spConnectionContainer->FindConnectionPoint(__uuidof(IWMPEvents), &m_spConnectionPoint);
    if (FAILED(hr))
    {
        // If not, try the _WMPOCXEvents interface, which uses IDispatch.
        hr = spConnectionContainer->FindConnectionPoint(__uuidof(_WMPOCXEvents), &m_spConnectionPoint);
    }
}

Finally, call IConnectionPoint::Advise to request events.

if(SUCCEEDED(hr))
{
    hr = m_spConnectionPoint->Advise(this, &m_dwAdviseCookie);
}

In the preceding example, the first parameter assumes that the calling class implements both IWMPEvents and _WMPOCXEvents. The second parameter is a return value that you use to stop listening to events, such as when your program exits, using code similar to the following:

// Stop listening to events
if (m_spConnectionPoint)
{
    if (0 != m_dwAdviseCookie)
        m_spConnectionPoint->Unadvise(m_dwAdviseCookie);
        m_spConnectionPoint.Release();
}

Implementing the event handlers for IWMPEvents and _WMPOCXEvents differs. For IWMPEvents, you must implement a function to handle every event defined by the interface, even if you don't intend to use the event.

// IWMPEvents methods
void STDMETHODCALLTYPE OpenStateChange( long NewState ){ return; }
void STDMETHODCALLTYPE PlayStateChange( long NewState ){ return; }
void STDMETHODCALLTYPE AudioLanguageChange( long LangID ){ return; }
// And so on...

To implement _WMPOCXEvents handlers, you must use IDispatch::Invoke, which is a single event handler implementation for all the events happening on the IDispatch interface. This means that you can choose to handle only certain events and ignore others. The following example code shows a _WMPOCXEvents handler, using Invoke, that handles only the OpenStateChange and PlayStateChange events:

HRESULT CMyClass::Invoke(
    DISPID  dispIdMember,      
    REFIID  riid,              
    LCID  lcid,                
    WORD  wFlags,              
    DISPPARAMS FAR*  pDispParams,  
    VARIANT FAR*  pVarResult,  
    EXCEPINFO FAR*  pExcepInfo,  
    unsigned int FAR*  puArgErr )
{
    if (!pDispParams)
        return E_POINTER;

    if (pDispParams->cNamedArgs != 0)
        return DISP_E_NONAMEDARGS;

    HRESULT hr = DISP_E_MEMBERNOTFOUND;

    switch (dispIdMember)
    {
        case DISPID_WMPCOREEVENT_OPENSTATECHANGE:
            OpenStateChange(pDispParams->rgvarg[0].lVal /* NewState */ );
            break;

        case DISPID_WMPCOREEVENT_PLAYSTATECHANGE:
            PlayStateChange(pDispParams->rgvarg[0].lVal /* NewState */);
            break;

        // Other cases can handle additional events by using DISPIDs.
    }

    return( hr );
}

In the preceding example code, each case simply calls through to the IWMPEvents handler for the corresponding event. If your code only handles _WMPOCXEvents, you can simply call a custom function or handle the event inline after the case statement.

Receiving Events from Windows Media Player 10 Mobile

The Windows Media Player 10 Mobile control only supports receiving certain events through _WMPOCXEvents and IWMPEvents. For more information, please see the documentation for IWMPEvents.

Samples

The Windows Media Player setup package installs a sample that demonstrates event handling. See the WMPHost sample for more information.

See Also

• Samples
• Using the Windows Media Player Control in a C++ Program

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