CODEWITHSUNDEEP
c#memory-managementcominterfacedirectshow
Amelse Etomer
Amelse Etomer

Reputation: 1253

ReleaseComObject does not work in static method

While testing my code, I came across a behavior that I find strange.

This:

if (_sampGrabber != null)
{
    Marshal.ReleaseComObject(_sampGrabber);
    _sampGrabber = null;
}

yields _sampGrabber==null, whereas after

ReleaseIfNotNull(_sampGrabber);

_sampGrabber still has its orignal value when using

public static int ReleaseIfNotNull(object comObject)
{
    int hr = 0;

    if (comObject != null)
    {
        hr = Marshal.ReleaseComObject(comObject);                
        comObject = null;
    }
    return hr;
}

_sampGrabber is a DirectShow SampleGrabber filter interface.

I am interested in an explanation for this behaviour. I came across it when writing tests using the Visual Studio Test Framework.

Upvotes: 2

Views: 95

Answers (1)

StuartLC
StuartLC

Reputation: 107277

If you need to change the reference, you will need to change the signature like so:

public static int ReleaseIfNotNull(ref object comObject)

Changing the local reference to comObject inside ReleaseIfNotNull affects only its own (stack) copy, and won't affect any other references to it. MSDN on ref and out

Upvotes: 4

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