CMediaControl Class

The CMediaControl class provides base class handling of the IDispatch methods of the dual-interface IMediaControl. It leaves as pure virtual the properties and methods of the IMediaControl interface.

Typically, the filter graph manager is the only object that implements the IMediaControl interface. (Filters implement the IMediaFilter interface, inherited by IBaseFilter, to receive control commands from the filter graph manager.) Therefore, this class library is of limited use to filter developers.

The CMediaControl::GetIDsOfNames, CMediaControl::GetTypeInfo, CMediaControl::GetTypeInfoCount, and CMediaControl::Invoke member functions are standard implementations of the IDispatch methods using the CBaseDispatch class (and a type library) to parse the commands and pass them to the pure virtual methods of the IMediaControl interface.

The IMediaControl methods, defined in control.odl, are left as pure virtual.

Member Functions

Name	Description
CMediaControl	Constructs a CMediaControl object.

Implemented INonDelegatingUnknown Methods

Name	Description
NonDelegatingQueryInterface	Returns a specified reference-counted interface.

Implemented IDispatch Methods

Name	Description
GetIDsOfNames	Maps a single member and an optional set of parameters to a corresponding set of integer dispatch identifiers (DISPIDs), which can be used during subsequent calls to the CMediaControl::Invoke method.
GetTypeInfo	Retrieves a type-information object, which can retrieve the type information for an interface.
GetTypeInfoCount	Retrieves the number of type-information interfaces provided by an object.
Invoke	Provides access to properties and methods exposed by an object.

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CMediaControl::CMediaControl

Constructs a CMediaControl object.

CMediaControl(
  const TCHAR *pName,
  LPUNKNOWN pUnk
  );

Parameters

pName

Name of the object for debugging purposes.

pUnk

Pointer to the owner of this object.

Return Values

No return value.

Remarks

Allocate the pName parameter in static memory. This name appears on the debugging terminal upon creation and deletion of the object.

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CMediaControl::GetIDsOfNames

Maps a single member function and an optional set of parameters to a corresponding set of integer dispatch identifiers (DISPIDs), which can be used upon subsequent calls to the CMediaControl::Invoke member function.

HRESULT GetIDsOfNames(
  REFIID riid,
  OLECHAR ** rgszNames,
  UINT cNames,
  LCID lcid,
  DISPID * rgdispid
  );

Parameters

riid

Reference identifier. Reserved for future use. Must be NULL.

rgszNames

Passed-in array of names to be mapped.

cNames

Count of the names to be mapped.

lcid

Locale context in which to interpret the names.

rgdispid

Caller-allocated array, each element of which contains an ID corresponding to one of the names passed in the rgszNames array. The first element represents the member name; the subsequent elements represent each of the member's parameters.

Return Values

Returns one of the following values.

Value	Meaning
DISP_E_UNKNOWN_CLSID	The CLSID was not recognized.
DISP_E_UNKNOWNNAME	One or more of the names were not known. The returned DISPIDs contain DISPID_UNKNOWN for each entry that corresponds to an unknown name.
E_OUTOFMEMORY	Out of memory.
S_OK	Success.

---

CMediaControl::GetTypeInfo

Retrieves a type-information object, which can retrieve the type information for an interface.

HRESULT GetTypeInfo(
  UINT itinfo,
  LCID lcid,
  ITypeInfo ** pptinfo
  );

Parameters

itinfo

Type information to return. Pass zero to retrieve type information for the IDispatch implementation.

lcid

Locale ID for the type information. An object might be able to return different type information for different languages. This is important for classes that support localized member names. For classes that do not support localized member names, this parameter can be ignored.

pptinfo

Pointer to the type-information object requested.

Return Values

Returns an HRESULT value.

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CMediaControl::GetTypeInfoCount

Retrieves the number of type-information interfaces provided by an object.

HRESULT GetTypeInfoCount(
  UINT * pctinfo
  );

Parameters

pctinfo

Pointer to the location that receives the number of type-information interfaces that the object provides. If the object provides type information, this number is 1; otherwise, the number is 0.

Return Values

Returns an HRESULT value.

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CMediaControl::Invoke

Provides access to properties and methods exposed by an object.

HRESULT Invoke(
  DISPID dispidMember,
  REFIID riid,
  LCID lcid,
  WORD wFlags,
  DISPPARAMS * pdispparams,
  VARIANT * pvarResult,
  EXCEPINFO * pexcepinfo,
  UINT * puArgErr
  );

Parameters

dispidMember

Identifier of the member. Use CMediaControl::GetIDsOfNames or the object's documentation to obtain the dispatch identifier.

riid

Reserved for future use. Must be IID_NULL.

lcid

Locale context in which to interpret arguments.

wFlags

Flags describing the context of the CMediaControl::Invoke call.

pdispparams

Pointer to a structure containing an array of arguments, an array of argument dispatch IDs for named arguments, and counts for number of elements in the arrays.

pvarResult

Pointer to where the result is to be stored, or NULL if the caller expects no result.

pexcepinfo

Pointer to a structure containing exception information.

puArgErr

Index of the first argument, within the rgvarg array, that has an error.

Return Values

Returns an HRESULT value.

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CMediaControl::NonDelegatingQueryInterface

Returns a specified reference-counted interface.

HRESULT NonDelegatingQueryInterface(
  REFIID riid,
  void **ppv
  );

Parameters

riid

Reference identifier.

ppv

Pointer to the interface.

Return Values

Returns pointers to the IMediaControl and IUnknown interfaces by default.

Remarks

Override this member function to publish any additional interfaces implemented by the derived class.

This member function implements the INonDelegatingUnknown::NonDelegatingQueryInterface method.

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