You need to provide a DependencyProperty of type WorkflowContext as shown below. Then use __Context as first parameter in above method. Check this for an example.
public static DependencyProperty __ContextProperty = System.Workflow.ComponentModel.DependencyProperty.Register("__Context",
typeof(WorkflowContext), typeof(ExpandSharePointGroup));
[Description("Context")]
[Browsable(true)]
[DesignerSerializationVisibility(DesignerSerializationVisibility.Visible)]
public WorkflowContext __Context
{
get
{
return ((WorkflowContext)(base.GetValue(__ContextProperty)));
}
set
{
base.SetValue(__ContextProperty, value);
}
}