Script task knows there is a variable but crashes if I attempt to use it - ssis

Question

setting up the container
Assigning the script variables
OK so no matter what I do with variables, my script task simply will not work with them. The error thrown is generic but as I'm working with SSDT I can't step through the code or do any reasonable debugging.
I have stripped this back to the point where I have uninstalled and reinstalled SSDT, and started with a new package from scratch, adding in a line of code at a time to the automatically generated code for the ScriptTask to ensure I'm not missing anything. Everything runs fine literally until I attempt to pull anything with a package variable, the code for which I've copied from the auto-help, and verified against SO and other sources.
"dts.Variables("User::variablename").value.toString()"
should work according to everything but I'm getting nowhere.
I've tried "User::FromFile", "FromFile", "Package::FromFile", "Project::FromFile" and "variables.item(1)" and none of the variations work either.
dts.variables.count shows that the script does know that there is a single variable there, and the variable does populate because I can get a subsequent data flow task to attempt opening files based on it.
Public Sub Main()
'
' Add your code here
'
Dim currFileName As String
Dim n As Integer
Dts.Events.FireInformation(0, "Script Task", "variables count: " & CType(Dts.Variables.Count, String), "", 0, True)
For n = 1 To Dts.Variables.Count
Dts.Events.FireInformation(0, "Script Task", CType(Dts.Variables.Item(n).Name.ToString, String) & " : " & CType(Dts.Variables.Item(n).Value, String), "", 0, True)
Next
' Debugging - assiging a file path explicity here does work so the loop and the code is fine
Dim filePath As String = "\\Path\File.csv"
Dts.Events.FireInformation(0, "Script Task", "Reading in file " & filePath, "", 0, True)
Try
currFileName = CType(Dts.Variables("FromFile").Value.ToString, String)
Catch
Dts.Events.FireError(999, "Reading Variable", "Can't read filename from variable name", "", 0)
End Try
Dts.Events.FireInformation(0, "Script Task", "Reading in file " & FilePath, "", 0, True)
Dim lines() As String = System.IO.File.ReadAllLines(filePath)
Dts.TaskResult = ScriptResults.Success
End Sub
Edit: Starting from scratch with the code below worked. However I am still not clear why previous attempts where I was using ".ToString()" or "CType(Dts.Variables("name of any variation").value,string)" weren't working.
Even when I wrapped all such attempts in Try-Catch loops I still got nowhere, where I would have expected VB to at least pick up the error but nothing.
Update #2
Currently on ... iteration 40(?) of "add one line/block of code in a try/catch and deal with the error". I'm still stuck why a try/catch would not prevent these invocation errors. Surely that's the whole point?
Update #3
Adding extra FireInformation events caused failures. Commenting them out didn't change the failures. Restarting VS and the script is completing in seconds ... having done nothing. Commenting out everything apart from #billinkc's code which works ... still does nothing. Losing the will to live here.
at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor)
at System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj,Object[] parameters, Object[] arguments)
at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
at System.RuntimeType.InvokeMember(String name, BindingFlags bindingFlags, Binder binder, Object target, Object[] providedArgs, ParameterModifier[] modifiers, CultureInfo culture, String[] namedParams)
at Microsoft.SqlServer.Dts.Tasks.ScriptTask.VSTATaskScriptingEngine.ExecuteScript()

Answer 1

I believe your root issue is that you're using the function ToString as a pointer and not invoking it. i.e. Value.ToString instead of Value.ToString() My VB is rusty so I could be off on that. Let's explore
I created an SSIS Variable, a package Parameter and a Project Parameter, all called FromFile and initialized them with strings to verify I am seeing expected values.
I added a Script Task, set the language to VB and added the above variables to my ReadOnlyVariables collection User::FromFile,$Package::FromFile,$Project::FromFile
I make great use of the following script within my SSIS packages. It enumerates through whatever variables it has access to and pushes the results to the OnInformation event stream. In Visual Studio, this will show in the Execution Results panel and the Output tab - which is way more useful. When running in the SSISDB, unless you've turned off Information events, you'll see it recorded in SSISDB.catalog.operation_messages
Public Sub Main()
Dim fireAgain As Boolean = False
For Each item As Variable In Dts.Variables
Dim template As String = "{0}::{1}->{2}"
Dim message As String = ""
message = String.Format(template, item.Namespace, item.Name, item.Value)
Dts.Events.FireInformation(0, "Scr Echo", message, "", 0, fireAgain)
Next
Dts.TaskResult = ScriptResults.Success
End Sub
In the Output tab, here's what I see
Information: 0x0 at SCR Echo Back, Scr Echo: $Package::FromFile->I am package parameter
Information: 0x0 at SCR Echo Back, Scr Echo: $Project::FromFile->I am project parameter
Information: 0x0 at SCR Echo Back, Scr Echo: User::FromFile->Hello world from Variable
As an added bonus, we see that the Parameters, Package:: and Project:: won't work because that's now how those parameters are addressed. The would be $Package::FromFile and $Project::FromFile
Now that I know I am correctly able to access the value of my variables or parameters, let's dig in an see if I can either reproduce your error or provide working code. I don't understand enough of what your code expects. You have two variables, filePath and currFileName. filePath is initialized to a fully qualified path, maybe? You're either going with a UNC but no share specified or a local path where you've half double escaped the slashes. We assign a value to currFileName which is from our Variable.
However, we use the filePath variable as the source for our ReadAllLines.
Public Sub Main()
Dim filePath As String = "C:\ssisdata\Input\SO_67660730.DoesNotExist.txt"
Dim fireAgain As Boolean = False
Dim lines() As String
If (False) Then
For Each item As Variable In Dts.Variables
Dim template As String = "{0}::{1}->{2}"
Dim message As String = ""
message = String.Format(template, item.Namespace, item.Name, item.Value)
Dts.Events.FireInformation(0, "Scr Echo", message, "", 0, fireAgain)
Next
End If
' Populate our filePath local variable with the value from the Variable collection
' Option A Blindly assume the first element in our collection is what we want
filePath = Dts.Variables(0).Value.ToString()
Dts.Events.FireInformation(0, "Option A", filePath, "", 0, fireAgain)
' Fully qualified named value
filePath = Dts.Variables("User::FromFile").Value.ToString()
Dts.Events.FireInformation(0, "Option B", filePath, "", 0, fireAgain)
' Either way, we have the file path available to us, let's read the data
If (System.IO.File.Exists(filePath)) Then
lines = System.IO.File.ReadAllLines(filePath)
Dts.Events.FireInformation(0, "Rows Read", lines.Length.ToString(), "", 0, fireAgain)
Else
Dts.Events.FireInformation(0, "No file found", filePath, "", 0, fireAgain)
End If
Dts.TaskResult = ScriptResults.Success
End Sub
Results being
Information: 0x0 at SCR Read File, Option A: C:\ssisdata\Input\SO_67660730.txt
Information: 0x0 at SCR Read File, Option B: C:\ssisdata\Input\SO_67660730.txt
Information: 0x0 at SCR Read File, Rows Read: 3
If you persist in using VB.NET as your language, you're going to be need to find blogs and samples that were built on 2005/2008 version of SSIS as that was the only language available to us. Most of the world has adopted C# as their primary language for SSIS Script and Tasks but Ben Weissman with Solisyon uses VB in his examples.