How to change SSIS variable values in C#

Question

I'm trying to set variables in code on an SSIS package I'm kicking off from C#.

Package pkg = app.LoadPackage(ConfigurationManager.AppSettings["SsisPkg"].ToString(), null);
pkg.Variables["User::FolderPath"].Value = Path.GetDirectoryName(e.FullPath);
pkg.Variables["User::FileName"].Value = Path.GetFileNameWithoutExtension(e.FullPath);

While debugging, I inspect the values directly after setting them, but nothing has changed. I can drill into the value (hover, navigate to it, edit value) so it doesn't seem to be that they aren't editable.

Any ideas what I'm doing wrong here?

Update: Thanks to billinkc, I'm comfortable what I'm doing should work so long as possibly other conditions are met. I've found that direct assignments in code fail (no error, just don't "take") and I cannot edit the values in the watch window. I can edit values when I'm inspecting them.

Could the actual issue be that there's a setting flagging these as read-only?

Answer Found: Needed to make the variables writable before setting the value:

        pkg.Variables["User::FileName"].EvaluateAsExpression = false;

Answer 1

You're doing it right. I created a basic SSIS package. Has one Variable, FolderPath, type string. There is a single script task that fires an Information event and the contents of that expose the value of the FolderPath variable

I then created a basic C# console app like this

public class InformationListener : DefaultEvents
{
    public override void OnInformation(DtsObject source, int informationCode, string subComponent, string description, string helpFile, int helpContext, string idofInterfaceWithError, ref bool fireAgain)
    {
        //base.OnInformation(source, informationCode, subComponent, description, helpFile, helpContext, idofInterfaceWithError, ref fireAgain);
        Console.WriteLine(string.Format("{0} {1}", subComponent, description));
    }

}

class Program
{
    static void Main(string[] args)
    {
        string sourcePackage = string.Empty;
        string path = string.Empty;
        string variableName = string.Empty;
        string designValue = string.Empty;
        string newValue = string.Empty;
        InformationListener listener = null;

        sourcePackage = @"J:\Src\SO\SSIS\Package.dtsx";
        path = @"J:\runtime";
        variableName = "User::FolderPath";
        listener = new InformationListener();

        Application app = new Application();
        Package pkg = null;
        Variable ssisVariable = null;
        pkg = app.LoadPackage(sourcePackage, null);

        ssisVariable = pkg.Variables[variableName];
        designValue = ssisVariable.Value.ToString();

        Console.WriteLine(string.Format("Designtime value = {0}", designValue));

        ssisVariable.Value = path;

        newValue = ssisVariable.Value.ToString();
        Console.WriteLine(string.Format("new value = {0}", newValue));

        DTSExecResult results = DTSExecResult.Canceled;

        results = pkg.Execute(null, null, listener, null, null);

        Console.WriteLine("Press any key to continue");
        Console.ReadKey();

    }
}

As you can tell from the variable inspection

and from my print statements

the design-time value of C:\designTime goes to J: because I forgot to escape my string above but we can pretend it shows J:\runtime.

All this said, unless we serialize the package with a call to the SaveToXml method, the value of User::FolderPath resets to the design time value once the object goes out of scope. Permanently updating would look like

app.SaveToXml(sourcePackage, pkg, null);

OP EDIT this discussion and examples led me to the answer: http://social.msdn.microsoft.com/Forums/sqlserver/en-US/dad8e218-1fe0-49db-89da-5715fb6d4b21/sql-2008-r2-ssis-c-script-task-not-setting-variable