How can I evaluate a string into an object in VBA?

Question

In my previous question, How do I assign a value to a property where the property name is supplied at runtime in VBA?, I learned to use CallByName to set a property in a class at run time.

This time, however, I'm trying to figure out how to get an object at run time from a string.

For example, let's say I have a string with the following data: Worksheets("RAW DATA").Range("A1").QueryTable.

Here's what I might try to do where the data above is the input for strParam below:

Function GetObject(strParam As String) As Object
    GetObject = SomeFunction(strParam)
End Function

In this case, GetObject should return a QueryTable when evaluated against Worksheets("RAW DATA").Range("A1").QueryTable. Is there anything in VBA that could take the place of SomeFunction from the example above?

Kyl

Not that I know of, but dude! Your code must be nuts to maintain!!! Are you sure Excel is the best tool for what you are trying to do??? – Cinquecento

Excel's certainly not the best solution from a "developer-friendly" programming approach. However, the end solution must be in Excel and it's something I'm familiar with. In this question, I'm trying to store "initialization variables" outside of the actual code as much as possible. It's been a good lesson in i-think-i'm-wasting-too-much-time-trying-to-make-this-perfect. – Kyl

I'm kind of intrigued...what exactly are you trying to do that you want to supply arbitrary VBA code at runtime? In your example it seems like you're just trying to get the QueryTable that goes with a given range, but that just means making the range address a parameter, not the whole VBA statement. You shouldn't need to go down the whole "soft coding" path... – Duckling

I just saw your previous comment. Things like "Worksheets" and "Range" and "QueryTable" definitely fall firmly into the category of "source code" and not "initialization variables". – Duckling

That's a very good point. I'm trying to automate part of the process involved with preparing a delivery manifest at our company. These have existed as Excel workbooks, so I'm writing code to read what order numbers are entered and auto-populate other fields with data from the database. I'm trying to keep it flexible and avoid "hard-coding" as much as possible (which works with simple types), but I think it's time to just get the job done. It's works fairly well anyway :) – Kyl

Related: https://mcmap.net/q/57308/-how-do-i-use-variables-to-set-properties-in-vba-excel/11683 (less features involved, but works). – Eighty

Answer 1

This time you're out of luck. There is no VBA equivalent of eval (not in Excel anyway...there is in Access VBA).

(Application.Evaluate() evaluates strings as Excel expressions, not as VBA code.)

Duckling

This may be a sign to stop trying to hack VBA and simply delivery a solution :) – Kyl

Answer 2

Active Scripting Engine can help you. Instantiate ScriptControl ActiveX, use .AddObject() method to add reference to Excel's Application object to the script control's execution environment, set the third parameter to True to make all Application's members accessible too. Then just use .Eval() method to evaluate any property or method, which is the Application's member. The example below shows evaluation of Worksheets() property:

Sub TestQueryTable()
    Dim objQueryTable As QueryTable
    Dim strEvalContent As String
    strEvalContent = "Worksheets(""RAW DATA"").Range(""A1"").QueryTable"
    Set objQueryTable = EvalObject(strEvalContent)
    objQueryTable.Refresh
    MsgBox objQueryTable.Connection
End Sub

Function EvalObject(strEvalContent As String) As Object
    With CreateObject("ScriptControl")
        .Language = "VBScript"
        .AddObject "app", Application, True
        Set EvalObject = .Eval(strEvalContent)
    End With
End Function

If you are on 64-bit Office, this answer may help you to get ScriptControl to work.

Cretan

This is great, but can it be used to instantiate custom-defined classes scoped to a specific Excel Workbook? – Hobgoblin

@Hobgoblin check this answer, it shows how to instantiate a class by name. – Cretan

Answer 3

There's the "Evaluate" method (or [ ] brackets). I don't think it will do exactly what you expect - as in run VBA code found in a string. You can look it up in the VBA help menu.

Roofer