Custom code running in PostSharp at build time can use the messaging facility to emit its own messages, warnings, and errors. These messages will appear in the MSBuild output and/or in Visual Studio. User-emitted warnings can be ignored or escalated using the same mechanism as for system messages.
Emitting messages
If you just have a few messages to emit, you may simply use one of the overloads of the Write method of the Message class.
All messages must have a severity SeverityType, a message number (used as a reference when ignoring or escalating messages), and a message text. Additionally, and preferably, messages may have a location (MessageLocation).
Note
To benefit from the possibility to ignore messages locally, you should always use provide a relevant location with your messages. Previous API overloads, which did not require a message location, are considered obsolete.
Tip
Do not use string.Format to format your messages. Instead, pass message arguments to the messaging facility, which will format some argument types, for instance reflection objects, in a more readable way.
Emitting messages using a message source
If you want the text of all messages to be stored in a single location, you have to emit messages through a MessageSource. Typically, you would create a singleton instance of MessageSource for each component, and associate each instance with a message dispenser. A message dispenser is a custom-written class implementing the IMessageDispenser interface. The MessageDispenser provides a convenient abstract implementation.
Note
Although it is tempting to use a ResourceManager as the backend of a message dispenser, comes with a non-negligible performance penalty because of the cost of instantiating the ResourceManager.