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POHow to make an ATL COM class derived from a base class?
 

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  1. POHow to make an ATL COM class derived from a base class?
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    <p>The "ATL simple object" wizard doesn't provide a way to specify that a new class is derived from an existing coclass and its interface. In Visual Studio 2008, how do I make a new ATL COM class derived from an existing one (i.e. <code>Base</code> implements <code>IBase</code>, and I want to make a new <code>Derived</code> class derived from <code>Base</code> that implements <code>IDerived</code>, where <code>IDerived</code> is derived from <code>IBase</code>.)</p> <p>Update: it sounds simple, but a wizard-generated ATL class has up to six base classes, a COM map and a connection point map. Which of these base classes and maps should be repeated in the derived class? If maps are repeated in the derived class should they contain the contents of the base class map or just the additional items? Does the order of base classes matter? What about <code>FinalConstruct()</code> and <code>FinalRelease()</code>? Should <code>DECLARE_PROTECT_FINAL_CONSTRUCT</code> and <code>DECLARE_REGISTRY_RESOURCEID</code> be repeated in the derived class?</p> <p>Here's a sample base class that is empty except for all the boilerplate. Now what should the derived class look like?</p> <pre><code>class ATL_NO_VTABLE CBase : public CComObjectRootEx&lt;CComSingleThreadModel&gt;, public CComCoClass&lt;CBase, &amp;CLSID_Base&gt;, public ISupportErrorInfo, public IConnectionPointContainerImpl&lt;CBase&gt;, public CProxy_IBaseEvents&lt;CBase&gt;, public IDispatchImpl&lt;IBase, &amp;IID_IBase, &amp;LIBID_ExampleLib, /*wMajor =*/ 1, /*wMinor =*/ 0&gt; { public: CBase() { } DECLARE_REGISTRY_RESOURCEID(IDR_Base) BEGIN_COM_MAP(CBase) COM_INTERFACE_ENTRY(IBase) COM_INTERFACE_ENTRY(IDispatch) COM_INTERFACE_ENTRY(ISupportErrorInfo) COM_INTERFACE_ENTRY(IConnectionPointContainer) END_COM_MAP() BEGIN_CONNECTION_POINT_MAP(CBase) CONNECTION_POINT_ENTRY(__uuidof(_IBaseEvents)) END_CONNECTION_POINT_MAP() // ISupportsErrorInfo STDMETHOD(InterfaceSupportsErrorInfo)(REFIID riid); DECLARE_PROTECT_FINAL_CONSTRUCT() HRESULT FinalConstruct() { return S_OK; } void FinalRelease() { } }; OBJECT_ENTRY_AUTO(__uuidof(Base), CBase) </code></pre>
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