Can you build an expression inside of a custom code function in Report Builder? - vb.net

Question

I need to provide my RDL files to teammates so that they can make minor customizations for each client. One of the ways I thought I might improve the efficiency is if I could build more complex expressions inside of custom code functions so that they can input some simple arguments and have the function handle the "heavy lifting" of adjusting the expression accordingly.
This is a very simple example, and not one I would take this step for, but I thought it the easiest place to start figuring out if I can make this work. For instance, in a tablix we want a count returned based on a value where the value is customized per client (and isn't a parameter).
=Count(iif(trim(Fields!Category.Value)="OPTIONA",1,nothing))
Is there a way I could build a function so that my teammates would just need to enter the following?
=Code.CustomFunction("OPTIONA")
My understanding is that the custom code in Report Builder can't query datasets, or at least not in the way that an expression within a tablix would be able to. I've built custom functions that work with the results of an expression added as the argument, but I can't seem to wrap my head around if there's a way to construct an expression within a custom function and pass it back to the expression.
For instance:
Public Function CustomFunction(field As String) As String
Dim customExpression As String = "Count(iif(trim(Fields!Category.Value)=" & field & ",1,nothing))"
Return customExpression
End Function
As expected, this just returns a string with the text of the expression, but not an executed expression. Is what I'm trying to achieve possible with Report Builder?
Or, as an alternative approach, can I somehow place variables at the beginning of an expression that are used later so that anyone else working on the expression just needs to worry about the beginning? Essentially create multiple custom functions and call them later on?
=Code.CustomFunction("OPTIONA",Count(iif(trim(Fields!Category.Value)=Code.CustFunc01(),1,nothing)))
Honestly not sure how I would go about building the functions themselves from here.

Answer 1

You can use a function instead of the related field. The function takes the field string as an argument and the filter string for which will increase the counter. Finally it returns the original field value
Private Dim Counter As Integer
Public Function SetCounter( Expr As String, Filter As String) As String
If Expr = Filter Then Counter = Counter + 1
Return Expr
End Function
Public Function GetCounter( ) As Integer
Return Counter
End Function
For the field value you can use the following expression (yellow color)
=Code.SetCounter( Fields!MyString.Value,"OPTION A")
To get the counter value you can either use the following expression calling a function (orange color)
= Code.GetCounter()
Or make the variable public and use Code.Counter as the expression