Updating External system from excel

Question

It's obviously possible from a demo i saw earlier but didn't catch enough details

I envision making a function call such as

=MyRTDReverse("keyvalue", "fieldName", [AC51])

or

=MyRTDReverse("keyvalue", [AB51], [AC51])  // where AB51 has the field name and AC51 has the field value

etc.

where updating the value in cell AC51 triggers a change

any samples/patterns on how this would work ?

Update - using .Net 3.5 + VSTO UPDATE 2 - would prefer to not use VSTO and instead make a UDF/RTD like call routine

Answer 1

To trigger something based on a value change in a cell, handle the Worksheet_Change event:

Private Sub Worksheet_Change(ByVal Target As Range) 
    'here, check whether Target, a Range, is one of your "trigger" cells,
    'and if it is, react accordingly
End Sub 

To define a custom function:

Function MyFunction(Argument1, Argument2)
    'do stuff with your arguments, and set MyFunction equal to the return value
End Function

In a cell, you can then use the function like = MyFunction("value", 3)