Question

I have a class and a set of IEnumerables that are using this class to give me a list in a list. (See this question‘s answer for details.)

Here is the code:

public IEnumerable<IEnumerable<WorkItemColumn>> EnumerateResultSet(WorkItemCollection queryResults)//DisplayFieldList displayFieldList)
{
    foreach (WorkItem workItem in queryResults)
    {
        yield return EnumerateColumns(queryResults.DisplayFields, workItem);   
    }
}

public IEnumerable<WorkItemColumn> EnumerateColumns(DisplayFieldList resultSet, WorkItem workItem)
{
    foreach (FieldDefinition column in resultSet)
        yield return new WorkItemColumn { Name = column.Name, Value = workItem[column.Name], WorkItemForColumn = workItem};
}

And the class:

public class WorkItemColumn
{
    public string Name { get; set; }
    public object Value { get; set; }
    public WorkItem WorkItemForColumn { get; set; }
}

I set this result to be the ItemsSource for my ListBox

Form.QueryResultListSource = EnumerateResultSet(queryResults);

The problem hits when I try to catch an event for this list box:

public void QueryResultsSelectionChanged(SelectionChangedEventArgs e)
{
                                                   +-----------------+
                                                   v                 | 
    foreach (WorkItemColumn workItemColumn in e.AddedItems)          |
    {                                                                |
        AddWorkItemToPad(workItemColumn.WorkItemForColumn);          |
    }                                                +---------------|
                                                     |               |
                                                     v               |    
    foreach (WorkItemColumn workItemColumn in e.RemovedItems)        |
    {                                                                |
        RemoveWorkItemFromPad(workItemColumn.WorkItemForColumn);     |
    }                                                                |
                                                                     |    
}                                                                    |
                                                                     |
These items are where the problem is --------------------------------+

When I examine e.AddedItems[0] while debugging and it says its type is EnumerateColumns.

When I try cast to that type Visual Studio says (understandably) that EnumerateColumns is a method but is used like a type.

So, how can I reference this by type so I can do a foreach loop and get at the stuff inside it?

---

This was my updated code based on the answer:

public void QueryResultsSelectionChanged(SelectionChangedEventArgs e)
{
    foreach (IEnumerable<WorkItemColumn> workItemColumns in e.AddedItems)
    {
        if (workItemColumns.Count() > 0)
            AddWorkItemToPad(workItemColumns.First().WorkItemForColumn);                
    }

    foreach (IEnumerable<WorkItemColumn> workItemColumns in e.RemovedItems)
    {
        if (workItemColumns.Count() > 0)
            RemoveWorkItemFromPad(workItemColumns.First().WorkItemForColumn);    
    }
}

Answer 1

The problem is that your first method isn’t yielding each result given by the first – it’s yielding the enumerable itself. The type of that a compiler-generated type for the iterator – but importantly, it implements IEnumerable<WorkItemColumn>.

You can cast each item to IEnumerable<WorkItemColumn> if you want – but it’s not really clear what you’re trying to do in QueryResultsSelectionChanged. You may want to do:

foreach (IEnumerable<WorkItemColumn> workItemColumns in e.AddedItems)
{                                                   
    foreach(WorkItemColumn workItemColumn in workItemColumns)
    {
        AddWorkItemToPad(workItemColumn.WorkItemForColumn); 
    }
}

etc… or you may not. It’s tricky to say without knowing what you’re really trying to do. Anyway, the crux of it is that you’re currently trying to treat a sequence of items as a single item. Don’t do that 🙂