[vbox-dev] Subject: Com api. Cannot use IDisplay. It's null

Pavel Murygin pavel.murygin at gmail.com
Fri Mar 8 22:12:40 PST 2013

Hi everybody!

I wrote a virtual box frontend in C# using com api. I haven't touched my
code for about a year. During that year I've moved to a laptop from pc.
Last time I ran my code it worked fine. Now I cannot access IDisplay
because it's null;
here is my code:

    var vb = new VirtualBoxClass();
    _machine = vb.FindMachine(machineName);

    var monitors = _machine.MonitorCount;

    Monitors = new MMFFrameBuffer[monitors];
    for (byte i = 0; i < monitors; i++)
        var name = string.Format("monitor{0}", i + 1);
        Monitors[i] = MMFFrameBuffer.CreateNew(name)

    _session = new SessionClass();
    _machine.LockMachine(_session, LockType.LockType_Shared);

    for (int i = 0; i < MonitorsCount; i++)
        _session.Console.Display.SetFramebuffer((uint) i, Monitors[i]);

My program fails on the line where I'm trying to set framebuffer. I get
NullreferenceException: _session.Console.Display is null.
My current version of Vbox is the latest: 4.2.8 r83876. I can't remember
the exact version on which my code ran correctly. I can only say It was the
latest one about 1 year ago. Host OS is Win7 pro x64 (same as it was on my
previous PC)

I'm completely clueless about my issue. Any help would be highly

Pavel Murygin.
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