Explicit Conversion

Question

Consider the following code:

using Microsoft.Office.Interop.Outlook;
using OutlookApp = Microsoft.Office.Interop.Outlook.Application;

namespace OutlookInterop
{
    class Program
    {
        static void Main(string[] args)
        {
            OutlookApp outlookApp = new OutlookApp();
            MailItem mailItem = outlookApp.CreateItem(OlItemType.olMailItem);
            mailItem.To = "test@test.com";
            mailItem.Subject = "Test Email Alert";
            mailItem.HTMLBody = "<html><body>Test email body.</body></html>";
            mailItem.Display(false);
        }
    }
}

This code works fine when I run it on Visual Studio, but when I use it in BluePrism, I get the following compiler error:

Page: Send Email Alert c#
Stage: Code1
Type: Error
Action: Validate
Description: Compiler error at line 2: Cannot implicitly convert type 'object' to 'Microsoft.Office.Interop.Outlook.MailItem'. An explicit conversion exists (are you missing a cast?)
Repairable: No

I think I have referenced the correct assemblies in BluePrism i.e.:

And then this is the code inside the actual code stage:

    OutlookApp outlookApp = new OutlookApp();
    MailItem mailItem = outlookApp.CreateItem(OlItemType.olMailItem); //this would be line 2
    mailItem.To = "test@test.com";
    mailItem.Subject = "Test Email Alert";
    mailItem.HTMLBody = "<html><body>Test email body.</body></html>";
    mailItem.Display(false);

So, why would that code work on Visual Studio but not in BluePrism? what is this cast that is missing?

score 7 · Accepted Answer · answered Jul 10 '19 at 10:41

I strongly suspect that the difference is in terms of how the Office library is imported. If you look at the properties for the reference in your Visual Studio project, I suspect it will show that the "Embed Interop Types" property is set to True. This not only embeds the interop types, but also makes methods and properties that would return object return dynamic instead - which is why the code would compile.

I don't know whether BluePrism has an option for COM libraries like that. If it doesn't, just at an explicit cast to MailItem.

I think you are right. I have imported and used COM libraries in BP before (Excel, Word) but I just never happened to come across this issue when creating instances of those objects.Thank you for the great explanation, is very helpful. — Badda_Bing, Jul 10 '19 at 11:15

score 3 · Answer 2 · answered Jul 10 '19 at 10:36

There is no implicit conversion so .Net doesn't know how to convert using simple assignment.

See this question for details of implicit vs explicit conversions;

However, the error states that there is an explicit conversion so you'll need to add an explicit cast to your code.

MailItem mailItem = (MailItem)outlookApp.CreateItem(OlItemType.olMailItem);

Explicit Conversion

2 Answers2