Question

We are using IoC and have our logging exposed with it. We are using Common.Logging and I have written a matching delegate for Common.Logging.FormatMessageHandler but I do not know how to convert from our version of that delegate to the one that the Common.Logging api is expecting.

This question appears to be similar but I do not understand how to convert from my implemented type to the known type that I want to call.
Dynamically casting one type of delegate to another

Here is my delegate signature:

public delegate string FormatMessageHandler(string format, params object[] args)

Here is Common.Logging’s:

public delegate string FormatMessageHandler(string format, params object[] args)

Same name (not that is matters) and same number of parameters. Both are known at compile time so it should be something obvious but I am not seeing it.

Answer 1

Why are you not using Common.Logging’s delegate in the first place if it is exactly the same?

However, a solution to your problem is to either use the dynamic cast explained in the article linked in the question you mentioned, or you do it like this:

YourNamespace.FormatMessageHandler yourHandler = ...;
Common.Logging.FormatMessageHandler handler = (f, a) => yourHandler(f, a);

UPDATE:
According to your comment, you want something like that:

public void Error(Action<Your.FormatMessageHandler> formatMessageCallback)
{
    _logger.Error(h => formatMessageCallback((f, a) => h(f, a)));
}

This will create a new action with one parameter h of type Common.Logging.FormatMessageHandler which calls the supplied action formatMessageCallback with a new delegate of Your.FormatMessageHandler that accepts two parameters f and a. This new delegate in turn calls h with the two supplied parameters.