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CEnumMediaTypes Class
This class provides the mechanism for enumerating the pin's preferred media types. Its constructor must be passed to an object from a class derived from CBasePin. It uses the virtual member function GetMediaType to retrieve each of the media types in turn. It also uses the pin's CBasePin::GetMediaTypeVersion member function to determine if the number or type of media types has changed.
The base pin class does not support dynamic media type changes. CBaseFilter::GetPinVersion always returns the same value, for example.
The media type enumerator must fill in a list of pointers to media type structures. The memory for those media type structures must be released by the callers when they have finished with it. However, the memory must not be allocated from any language-specific heap; otherwise, problems might occur between a filter written in C and another written in C++. For this reason, the base classes provide generic functions (not member functions of a class) to create and delete media types: CreateMediaType and DeleteMediaType. These manage memory allocation from the task allocator.
All member functions in this class that return HRESULT and accept a pointer as a parameter return E_POINTER when passed a null pointer.
Member Functions
Name Description CEnumMediaTypes Constructs a CEnumMediaTypes object. Implemented IUnknown Methods
Name Description AddRef Increments the reference count. QueryInterface Returns pointers to supported interfaces. Release Decrements the reference count. Implemented IEnumMediaTypes Methods
Name Description Clone Creates a duplicate CEnumMediaTypes object with the same state. Next Returns the next media type after the current position. Reset Sets the current position back to the beginning. Skip Skips over one or more entries in the enumerator. CEnumMediaTypes Class
CEnumMediaTypes::AddRefIncrements the reference count for the calling interface on an object. It should be called for every new copy of a pointer to an interface on a given object.
ULONG AddRef(void);
Return Values
Returns an integer from 1 to n, the value of the new reference count. This information is meant to be used for diagnostic/testing purposes only, because, in certain situations, the value might be unstable.
Remarks
This member function implements the IUnknown::AddRef method.
CEnumMediaTypes Class
CEnumMediaTypes::CEnumMediaTypesConstructs a CEnumMediaTypes object.
CEnumMediaTypes(
CBasePin *pPin,
CEnumMediaTypes *pEnumMediaTypes
);Parameters
- pPin
- Pointer to the pin on which the enumeration is to be performed.
- pEnumMediaTypes
- Pointer to the instantiated CEnumMediaTypes object.
Return Values
No return value.
Remarks
This is a standard class constructor.
CEnumMediaTypes Class
CEnumMediaTypes::CloneRetrieves another enumerator containing the same enumeration state as the current one.
HRESULT Clone(
IEnumMediaTypes ** ppEnum
);Parameters
- ppEnum
- New copy of the enumerator.
Return Values
Returns an HRESULT value.
Remarks
This member function implements the IEnumMediaTypes::Clone method.
CEnumMediaTypes Class
CEnumMediaTypes::NextRetrieves the specified number of items in the enumeration sequence.
HRESULT Next(
ULONG cMediaTypes,
AM_MEDIA_TYPE** ppMediaTypes,
ULONG * pcFetched
);Parameters
- cMediaTypes
- Number of media types to place.
- ppMediaTypes
- Array in which to place the next media type or types.
- pcFetched
- Actual count passed.
Return Values
Returns an HRESULT value.
Remarks
This member function implements the IEnumMediaTypes::Next method. To call this method, pass a pointer's address to a media type. The base class implementation relies on the existence of an overridden CBasePin::GetMediaType member function in the derived class that will provide the next media type.
Free each media type acquired by calling DeleteMediaType, which will free the format block and the media type itself.
CEnumMediaTypes Class
CEnumMediaTypes::QueryInterfaceRetrieves a pointer to a specified interface on a component to which a client currently holds an interface pointer.
HRESULT QueryInterface(
REFIID iid,
void ** ppvObject
);Parameters
- iid
- Specifies the IID of the interface being requested.
- ppvObject
- Receives a pointer to an interface pointer to the object on return. If the interface specified in iid is not supported by the object, ppvObject is set to NULL.
Return Values
Returns S_OK if the interface is supported, S_FALSE if not.
Remarks
This member function implements the IUnknown::QueryInterface method and passes out references to the IEnumMediaTypes interface. Override this class to return other interfaces on the object in the derived class.
CEnumMediaTypes Class
CEnumMediaTypes::ReleaseDecrements the reference count for the calling interface on an object. If the reference count on the object falls to zero, the object is freed from memory.
ULONG Release(void);
Return Values
Returns the resulting value of the reference count, which is used for diagnostic/testing purposes only. If you need to know that resources have been freed, use an interface with higher-level semantics.
Remarks
This member function implements the IUnknown::Release method.
CEnumMediaTypes Class
CEnumMediaTypes::ResetResets the enumerator to the beginning so that the next call to the IEnumMediaTypes::Next method will return, at a minimum, the first media type in the enumeration.
HRESULT Reset(void);
Return Values
Returns S_OK if successful; otherwise, returns S_FALSE.
Remarks
This member function implements the IEnumMediaTypes::Reset method.
CEnumMediaTypes Class
CEnumMediaTypes::SkipSkips a specified number of elements in the enumeration sequence.
HRESULT Skip(
ULONG cMediaTypes
);Parameters
- cMediaTypes
- Number of media type elements to skip.
Return Values
Returns an HRESULT value.
Remarks
This member function implements the IEnumMediaTypes::Skip method.
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