Question

I have a Windows Workflow application that uses classes I’ve written for COM automation. I’m opening Word and Excel from my classes using COM.

I’m currently implementing IDisposable in my COM helper and using Marshal.ReleaseComObject(). However, if my Workflow fails, the Dispose() method isn’t being called and the Word or Excel handles stay open and my application hangs.

The solution to this problem is pretty straightforward, but rather than just solve it, I’d like to learn something and gain insight into the right way to work with COM. I’m looking for the ‘best’ or most efficient and safest way to handle the lifecycle of the classes that own the COM handles. Patterns, best practices, or sample code would be helpful.

Answer 1

I can not see what failure you have that does not calls the Dispose() method. I made a test with a sequential workflow that contains only a code activity which just throws an exception and the Dispose() method of my workflow is called twice (this is because of the standard WorkflowTerminated event handler). Check the following code:

Program.cs

    class Program     {         static void Main(string[] args)         {             using(WorkflowRuntime workflowRuntime = new WorkflowRuntime())             {                 AutoResetEvent waitHandle = new AutoResetEvent(false);                 workflowRuntime.WorkflowCompleted += delegate(object sender, WorkflowCompletedEventArgs e)                  {                     waitHandle.Set();                 };                 workflowRuntime.WorkflowTerminated += delegate(object sender, WorkflowTerminatedEventArgs e)                 {                     Console.WriteLine(e.Exception.Message);                     waitHandle.Set();                 };                  WorkflowInstance instance = workflowRuntime.CreateWorkflow(typeof(WorkflowConsoleApplication1.Workflow1));                 instance.Start();                  waitHandle.WaitOne();             }             Console.ReadKey();         }     } 

Workflow1.cs

    public sealed partial class Workflow1: SequentialWorkflowActivity     {         public Workflow1()         {             InitializeComponent();             this.codeActivity1.ExecuteCode += new System.EventHandler(this.codeActivity1_ExecuteCode);         }          [DebuggerStepThrough()]         private void codeActivity1_ExecuteCode(object sender, EventArgs e)         {             Console.WriteLine('Throw ApplicationException.');             throw new ApplicationException();         }          protected override void Dispose(bool disposing)         {             if (disposing)             {                 // Here you must free your resources                  // by calling your COM helper Dispose() method                 Console.WriteLine('Object disposed.');             }         }     } 

Am I missing something? Concerning the lifecycle-related methods of an Activity (and consequently of a Workflow) object, please check this post: Activity ‘Lifetime’ Methods. If you just want a generic article about disposing, check this.