Multi-Part message – “use of unconstructed message ” – Error message when you try to build a BizTalk project

Sometimes, when we try to build or deploya BizTalk solution, we may get the following error message:

“Use of Unconstructed Message ‘MessageName’”

I get this error when I try to construct a multi-part message for sending an email with a body and an attachment.

Cause

There is a common issue when we are developing a BizTalk Server project in Visual Studio. And the reason is that Visual Studio is trying to use a message that has not yet been initialized, or it will “think” that, based on your flow, maybe situations that it will not be initialized.

Solution

Check if you have a reference to the message before its initialize, for example:

myMessage.Body(Microsoft.XLANGs.BaseTypes.ContentType) = "text/plain";
myMessage.Body = new …;

Correct syntax:

myMessage.Body = new …;
myMessage.Body(Microsoft.XLANGs.BaseTypes.ContentType) = "text/plain";

My suggestion is, first, initialize both types of the multi-part message, in my case:

myMessage.Body = new Microsoft.XLANGs.CustomFormattersSDK.RawString(“”);
myMessage.Attachment = new System.Xml.XmlDocument();

and then I define other properties of the message:

myMessage(SMTP.Subject) = …;

and magic appends!! Problem solved.

Another Solution

I suggest not to use, but, if you’re positive that your response message will always have a value, you could instantiate the message inside a construct shape, using:

myMessage.Body = null;
myMessage.Attachment = null