TaoWen's Blog

someone told me, don't do that. Framework should free the com reference for you. but...

if you are writing a AddIn for PowerPoint, you might have seen the same problem. That is, if you reference a element of GroupItems without release it immediately, next time, you group it into bigger group, and trying to reference the GroupItems of the biggger group, PowerPoint totally screwed up. Here is the common solution for such kind of situation.

The idea is using your own object to wrap RCW(raw com wrapper). In the constructor, you register yourself in the ComObjectsPool. When you want to clean things up, clean com objects from the pool.

    public interface IComObject : IDisposable
    {
        bool Release();
    }

    public abstract class ComObject : IComObject
    {
        private bool shouldRelease = true;
        public abstract void Dispose();

        public ComObject()
        {
            ComObjectsPool.PutIn(this);
        }

        public bool Release()
        {
            if (shouldRelease)
            {
                Dispose();
                return true;
            }
            return false;
        }

        public bool ShouldRelease
        {
            get { return shouldRelease; }
            set { shouldRelease = value; }
        }
    }

    public static class ComObjectsPool
    {
        private static readonly List<IComObject> comObjects = new List<IComObject>();

        public static void PutIn(IComObject comObject)
        {
            comObjects.Add(comObject);
        }

        public static void ReleaseAll()
        {
            List<IComObject> unreleasedComObjects = new List<IComObject>();
            foreach (IComObject comObject in comObjects)
            {
                if (!comObject.Release())
                {
                    unreleasedComObjects.Add(comObject);
                }
            }
            comObjects.Clear();
            comObjects.AddRange(unreleasedComObjects);
        }
    }

    public class AdaptedShape : ComObject, IShape
    {
        private readonly Shape shape;

        public AdaptedShape(Shape shape)
        {
            this.shape = shape;
        }

        public override void Dispose()
        {
            Marshal.ReleaseComObject(shape);
        }
    }