C# Excel automation causes Excel memory leak

Question

I\'m trying to use C# with the COM Interop library to open a set of very heavy excel workbooks. I have to use C#, because I also need to start macros, move some cells aroun

Answer 1

When using the MS Office COM Interop libraries, there are a couple of things I've come across to avoid the memory leaks:

First, "Don't use two dots" is the best way to remember it, but basically, always assign a new COM object reference to a new variable, do not chain-call members, even if Intellisense encourages it. Chained calling does some stuff in the background that prevents proper release by the .NET framework.. Here is some code I use for starting an Excel report:

//use vars for every COM object so references don't get leftover
//main Excel app
var excelApp = new Application();
var workbooks = excelApp.Workbooks;

//workbook template
var wbReport = workbooks.Add(@"C:\MyTemplate.xltx");

//Sheets objects for workbook
var wSheetsReport = wbReport.Sheets;
var wsReport = (Worksheet)wSheetsReport.get_Item("Sheet1");

Secondly, Call Marshal.ReleaseComObject() for each variable created in reverse order of creation, and call a couple of garbage collection methods before doing so:

//garbage collector
GC.Collect();
GC.WaitForPendingFinalizers();

//cleanup
Marshal.ReleaseComObject(wsReport);
Marshal.ReleaseComObject(wSheetsReport);
Marshal.ReleaseComObject(wbReport);
Marshal.ReleaseComObject(workbooks);
Marshal.ReleaseComObject(excelApp);

Using this scheme every time I use Excel has solved my memory issues, though it is tedious and sad we can't use the chained members the way we're used to.