[DirectShow] 038 - Enumerating Filters

The Filter Graph Manager supports the IFilterGraph::EnumFilters

method, which enumerates all the filters in the filter graph. It returns a
pointer to the IEnumFilters

interface. The IEnumFilters::Next

method retrieves IBaseFilter

interface pointers.

Filter Graph Manger
支持
IFilterGraph::EnumFilters
方法用来枚举
filter graph
中的所有
filter
。这个函数返回
IEnumFilters
接口的指针。
IEnumFilters::Next
方法返回
IBaseFilter
接口指针。

The following example shows a function that enumerates the filters
in a graph and displays a message box with each filter's name. It uses the IBaseFilter::QueryFilterInfo

method to retrieve the name of the filter. Note the places where the function
calls Release
on an interface to decrement the reference count.

下面的列子展现枚举
graph
中
filter
的方法并在一个消息框中显示每个
filter
名字。使用
IBaseFilter::QueryFilterInfo
方法获得
filter
的名字。记得调用
Release
来消耗应用计数。

HRESULT EnumFilters (IFilterGraph *pGraph)
{
IEnumFilters *pEnum = NULL;
IBaseFilter *pFilter;
ULONG cFetched;
HRESULT hr = pGraph->EnumFilters(&pEnum);
if (FAILED(hr)) return hr;
while(pEnum->Next(1, &pFilter, &cFetched) == S_OK)
{
FILTER_INFO FilterInfo;
hr = pFilter->QueryFilterInfo(&FilterInfo);
if (FAILED(hr))
{
MessageBox(NULL, TEXT("Could not get the filter info"),
TEXT("Error"), MB_OK | MB_ICONERROR);
continue;  // Maybe the next one will work.
}
#ifdef UNICODE
MessageBox(NULL, FilterInfo.achName, TEXT("Filter Name"), MB_OK);
#else
char szName[MAX_FILTER_NAME];
int cch = WideCharToMultiByte(CP_ACP, 0, FilterInfo.achName,
MAX_FILTER_NAME, szName, MAX_FILTER_NAME, 0, 0);
if (chh > 0)
MessageBox(NULL, szName, TEXT("Filter Name"), MB_OK);
#endif
// The FILTER_INFO structure holds a pointer to the Filter Graph
// Manager, with a reference count that must be released.
if (FilterInfo.pGraph != NULL)
{
FilterInfo.pGraph->Release();
}
pFilter->Release();
}
pEnum->Release();
return S_OK;
}