Properly clean up excel interop objects revisited: Wrapper objects
- by chiccodoro
Hi all,
Excel 2007 Hangs When Closing via .NET
How to properly clean up Excel interop objects in C#
How to properly clean up interop objects in C#
All of these struggle with the problem that C# does not release the Excel COM objects properly after using them. There are mainly two directions of working around this issue:
Kill the Excel process when Excel is not used anymore.
Take care to assign each COM object used explicitly to a variable and to Marshal.ReleaseComObject all of these.
Some have stated that 2 is too tedious and there is always some uncertainty whether you forget to stick to this rule at some places in the code. Still 1 seems dirty and dangerous to me, also I could imagine that in an environment with restricted access killing processes is not allowed.
So I've been thinking about solving 2 by creating another proxy object model which mimics the Excel object model (for me, it would suffice to implement the objects I actually need). The principle would look as follows:
Each Excel Interop class has its proxy which wraps an object of that class.
The proxy releases the COM object in its destructor.
The proxy mimics the interface of the Interop class (maybe by inheriting it).
Any methods that usually return another COM object return a proxy instead. The other methods simply delegate the implementation to the inner COM object.
This is a rough sketch of the code:
public class Application : Microsoft.Office.Interop.Excel.Application
{
private Microsoft.Office.Interop.Excel.Application innerApplication
= new Microsoft.Office.Interop.Excel.Application innerApplication();
~Application()
{
Marshal.ReleaseCOMObject(innerApplication);
}
public Workbooks Workbooks
{
get { return new Workbooks(innerApplication.Workbooks); }
}
}
public class Workbooks
{
private Microsoft.Office.Interop.Excel.Workbooks innerWorkbooks;
Workbooks(Microsoft.Office.Interop.Excel.Workbooks innerWorkbooks)
{
this.innerWorkbooks = innerWorkbooks;
}
~Workbooks()
{
Marshal.ReleaseCOMObject(innerWorkbooks);
}
}
My questions to you are in particular:
Who finds this a bad idea and why?
Who finds this a gread idea? If so, why hasn't anybody implemented/published such a model yet? Just due to the effort, or am I missing a killing problem with that idea?
Is it impossible/bad/dangerous to do the ReleaseCOMObject in the destructor? (I've only seen proposals to put it in a Dispose() rather than in a destructor - why?)
If the approach makes sense, any suggestions to improve it?
