我是否需要在每个“foreach”上释放 COM 对象？迭代？

Question

这是（潜在的）问题：

我创建一个 COM 对象，然后使用“foreach”迭代它返回的集合中的每个元素。我是否需要释放集合中迭代的每个单独元素？ （参见下面的代码。）如果是这样，我想不出一种方法可以有效地从“finally”语句中释放它，以防在操作该项目时出现错误。

有什么建议吗？

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

    try
    {
        manager = new ComObjectClass();
        foreach (ComObject item in manager.GetCollectionOfItems())
        {
            Log.Debug(item.Name);
            releaseComObject(item); // <-- Do I need this line?
                                    //     It isn't in a 'finally' block...
                                    //             ...Possible memory leak?
        }
    }
    catch (Exception) { }
    finally
    {
        releaseComObject(manager);
    }
}

private static void releaseComObject(object instance)
{
    if (instance != null)
    {
        try
        {
            System.Runtime.InteropServices.Marshal.ReleaseComObject(instance);
        }
        catch
        {
            /* log potential memory leak */
            Log.Debug("Potential memory leak: Unable to release COM object.");
        }
        finally
        {
            instance = null;
        }
    }
}

Answer 1

您不应该对 COM 对象使用 foreach 语句，因为引用是在幕后进行的，您无法控制释放。我会切换到 for 循环并确保您 永远不要对 COM 对象使用两个点。

其外观如下：

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);
}

Answer 2

另一种方法是创建您自己的迭代器函数：

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);
    }
}

我觉得这使您的代码更具可读性，特别是当您需要多次迭代子项时。