Error handling in asynchronous activities

Providing error handling in an AsyncCodeActivity involves routing the error through the activity’s callback system. This topic describes how to get an error that is thrown in an asynchronous operation back to the host, using the SendMail activity sample.

Returning an error thrown in an asynchronous activity back to the host

Routing an error in an asynchronous operation back to the host in the SendMail activity sample involves the following steps:

• Add an Exception property to the SendMailAsyncResult class.

• Copy the thrown error to that property in the SendCompleted event handler.

• Throw the exception in the EndExecute event handler.

The resulting code is as follows.

class SendMailAsyncResult : IAsyncResult  
        {  
            …  
            public Exception Error { get; set; }
            …  
            void SendCompleted(object sender, AsyncCompletedEventArgs e)  
            {  
                Error = e.Error;  
                this.asyncWaitHandle.Set();  
                callback(this);  
            }  
         }  
  
    public sealed class SendMail: AsyncCodeActivity  
    {  
         …  
        protected override void EndExecute(AsyncCodeActivityContext context, IAsyncResult result)  
        {  
            SendMailAsyncResult sendMailResult = result as SendMailAsyncResult;  
            if (sendMailResult != null && sendMailResult.Error != null)  
                throw sendMailResult.Error;
        }  
    }