Question

I have the following code. I enclosed it in a try block and “try” to catch exceptions:

            try
            {
                var response = query.Execute() as QueryOperationResponse;
            }
            catch (System.Net.WebException s)
            {
                var se = e;
                se = se + "aa";
            }
            catch (Exception e)
            {
                var a = e;
                a = a + "ab";
            }

When the query.Execute line executes it produces an exception and VS2010 stops on the line starting with catch (System.Net and gives the following:

System.Data.Services.Client.DataServiceQueryException was unhandled by user code
  Message=An error occurred while processing this request.
  Source=System.Data.Services.Client
  StackTrace:
       at System.Data.Services.Client.DataServiceRequest.Execute[TElement](DataServiceContext context, QueryComponents queryComponents)
       at System.Data.Services.Client.DataServiceQuery`1.Execute()

When I step through I expect it to go to the code “var se = 2;” or “var a = e”. However the next line after when I step through with F11 is a jump completely out of that code block / method.

Why doesn’t the exception fall into one of the catch buckets? I am totally confused.

Answer 1

DataServiceQuery.Execute() is an asynchronous method, in which you will have to either pass a delegate and call e.MarkErrorAsHandled(). Exception is shown later on and it is not in the same execution pipeline.

And e.Error will contain the thrown exception.

query.Execute( e=>{
    MessageBox.Show(e.Error.ToString());
    e.MarkErrorAsHandled();
});

or

response = query.Execute();
response.Loaded += e=>{
    MessageBox.Show(e.Error.ToString());
    e.MarkErrorAsHandled();
};

Exact names must be different but they will show up on intellisense.