Do I need to release the COM object on every 'foreach' iteration?

Question

Here\'s the (potential) problem:

I create a COM object, and then use a \'foreach\' to iterate through each element in a collection it returns. Do I need to release

Answer 1

Another way is to create your own iterator function :

IEnumerable<ComObject> GetChildItems(this ComObjectClass manager) {
    ComObject comObject = null;

    ComObject[] collectionOfComItems = manager.GetCollectionOfItems();
    for (int i = 0; i < collectionOfComItems.Length; i++) {
        try {
            comObject = collectionOfComItems[i];

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

    yield break;
}

private static void doStuff() {
    ComObjectClass manager = null;

    try {
        manager = new ComObjectClass();

        foreach (ComObject item in manager.GetChildItems()) {
            Log.Debug(item.Name);
        }
    } finally {
        releaseComObject(manager);
    }
}

I feel this makes your code much more readable, especially if you need to iterate through the child items at multiple times.

Answer 2

You should not use a foreach statement with a COM object, as a reference is made behind the scenes to which you have no control over releasing. I would switch to a for loop and make sure you never use two dots with COM objects.

The way this would look would be:

try
{
    manager = new ComObjectClass();
    ComObject comObject = null;
    ComObject[] collectionOfComItems = manager.GetCollectionOfItems();
    try
    {
        for(int i = 0; i < collectionOfComItems.Count; i++)
        {
            comObject = collectionOfComItems[i];
            ReleaseComObject(comObject);
        }
    }            
    finally
    {
        ReleaseComObject(comObject);
    }
}
finally 
{
    ReleaseComObject(manager);
}