IDispatchInvoke

IDispatchInvoke is a commonly used term for the IDispatch::Invoke method of the COM IDispatch interface. It refers to the late-bound invocation mechanism that enables callers to call methods or access properties on automation objects at runtime, using DISPIDs rather than compile-time interfaces. This mechanism is central to scripting engines, such as JavaScript or VBScript, and to interoperation with COM servers that expose automation interfaces.

The standard method signature is HRESULT Invoke(DISPID dispIdMember, REFIID riid, LCID lcid, WORD wFlags, DISPPARAMS* pDispParams, VARIANT* pVarResult, EXCEPINFO* pExcepInfo, UINT* puArgErr). For IDispatch::Invoke, riid must be IID_NULL. The wFlags parameter indicates the kind of invocation requested, such as DISPATCH_METHOD, DISPATCH_PROPERTYGET, DISPATCH_PROPERTYPUT, or DISPATCH_PROPERTYPUTREF.

Arguments are supplied through the DISPPARAMS structure, which contains cArgs and cNamedArgs, as well as rgvarg, a VARIANTARG array of arguments in reverse order, and rgdispidNamedArgs, an array of DISPIDs for any named arguments. If a name is used in lieu of a DISPID, GetIDsOfNames is used to obtain the corresponding DISPID before calling Invoke.

On success, pVarResult receives any return value. If an error occurs, the method returns a COM error code, and pExcepInfo may be filled with exception information; puArgErr indicates which argument caused a type or binding error in certain DISP_E_* scenarios.

IDispatch::Invoke is widely used in automation scenarios and interop layers. Proper usage requires correct argument ordering, careful memory management for VARIANTs, and adherence to the constraints on riid and DISPATCH flags. Note that IDispatchInvoke is an informal reference to this invocation mechanism, not a separate standard interface.