使用 DirectShow 获取过滤器（com 设备）

Question

来自 code project 我得到了这段代码，但是 我不明白。

此函数将在其类别之后获取所有过滤器（com 设备）并将其填充到 innerlist

谁能详细解释一下我搜索过的每个部分对我来说都是新的我不明白什么是 ICreateDevEnum ，UCOMIEnumMoniker 和 UCOMIMoniker 以及 我们如何使用它们获得过滤器

protected void getFilters(Guid category)
        {
            int                 hr;
            object              comObj = null;
            ICreateDevEnum      enumDev = null;
            UCOMIEnumMoniker    enumMon = null;
            UCOMIMoniker[]      mon = new UCOMIMoniker[1];

            try 
            {
                // Get the system device enumerator
                Type srvType = Type.GetTypeFromCLSID( Clsid.SystemDeviceEnum );
                if( srvType == null )
                    throw new NotImplementedException( "System Device Enumerator" );
                comObj = Activator.CreateInstance( srvType );
                enumDev = (ICreateDevEnum) comObj;

                // Create an enumerator to find filters in category
                hr = enumDev.CreateClassEnumerator( ref category, out enumMon, 0 );
                if( hr != 0 )
                    throw new NotSupportedException( "No devices of the category" );

                // Loop through the enumerator
                int f;
                do
                {
                    // Next filter
                    hr = enumMon.Next( 1, mon, out f );
                    if( (hr != 0) || (mon[0] == null) )
                        break;

                    // Add the filter
                    Filter filter = new Filter( mon[0] );
                    InnerList.Add( filter );

                    // Release resources
                    Marshal.ReleaseComObject( mon[0] );
                    mon[0] = null;
                }
                while(true);

                // Sort
                InnerList.Sort();
            }
            finally
            {
                enumDev = null;
                if( mon[0] != null )
                    Marshal.ReleaseComObject( mon[0] ); mon[0] = null;
                if( enumMon != null )
                    Marshal.ReleaseComObject( enumMon ); enumMon = null;
                if( comObj != null )
                    Marshal.ReleaseComObject( comObj ); comObj = null;
            }
        }

Answer 1

您在本机 API 上使用 [未记录] 托管包装器，但是 API 本身在 MSDN 上有详细记录，并且接口名称具有直接映射。

参见 Using the System Device Enumerator，其中描述了相关标识符。

To use the System Device Enumerator, do the following:

Create the system device enumerator by calling CoCreateInstance. The class identifier (CLSID) is CLSID_SystemDeviceEnum.

Obtain a category enumerator by calling ICreateDevEnum::CreateClassEnumerator with the CLSID of the desired category. This method returns an IEnumMoniker interface pointer. If the category is empty (or does not exist), the method returns S_FALSE rather than an error code. If so, the returned IEnumMoniker pointer is NULL and dereferencing it will cause an exception. [...]

使用 DirectShow 获取过滤器（com 设备）

get filters(com devices) using DirectShow

c#

com

directshow

filter