Question

Backstory: I’m using log4net to handle all logging for a project I’m working on. One particular method can be called under several different circumstances — some that warrant the log messages to be errors and others that warrant the log messages to be warnings.

So, as an example, how could I turn

Public Sub CheckDifference(ByVal A As Integer, ByVal B As Integer)   If (B - A) > 5 Then     log.ErrorFormat('Difference ({0}) is outside of acceptable range.', (B - A))   End If End Sub 

Into something more along the lines of:

Public Sub CheckDifference(ByVal A As Integer, ByVal B As Integer, 'Some delegate info here')   If (B - A) > 5 Then     **delegateinfo**.Invoke('Difference ({0}) is outside of acceptable range.', (B - A))   End If End Sub 

So that I could call it and pass either log.ErrorFormat or log.WarnFormat as the delegate?

I’m using VB.NET with VS 2008 and .NET 3.5 SP1. Also, I’m fairly new to delegates in general, so if this question should be worded differently to remove any ambiguities, let me know.

EDIT: Also, how could I initialize the delegate to either the ErrorFormat or the WarnFormat in the class constructor? Would it be as easy as myDelegate = log.ErrorFormat? I would imagine there is more to it than that (pardon my ignorance on the subject — delegates are really something I want to learn more about, but so far they have eluded my understanding).

Answer 1

Declare your delegate signature:

Public Delegate Sub Format(ByVal value As String) 

Define your Test function:

Public Sub CheckDifference(ByVal A As Integer, _                            ByVal B As Integer, _                            ByVal format As Format)     If (B - A) > 5 Then         format.Invoke(String.Format( _         'Difference ({0}) is outside of acceptable range.', (B - A)))     End If End Sub 

Somewhere in your code call your Test function:

CheckDifference(Foo, Bar, AddressOf log.WriteWarn) 

Or

CheckDifference(Foo, Bar, AddressOf log.WriteError)