Question

I have a class, ExpenseItem and a list based off that class.

I’m currently designing a form that has a combo box that would allow me to select a particular type of ExpenseItem Trip, and show all results in a listbox.

Form Code (tripSelect is the combo box and listExpenses is the list box):

    private void LoadExpenseList()
    {
        tripSelect.Items.Clear();
        var dateSorted =
            from e in roster
            group e by e.Trip into tripGroup
            select new { Trip = tripGroup.Key };
        foreach (var e in dateSorted)
            tripSelect.Items.Add(e.Trip);
    }

    private void LoadExpenseDetail()
    {
        listExpenses.Items.Clear();
        var dateSorted =
            from e in roster
            orderby e.Trip
            select e;
        foreach (var e in dateSorted) ;
    }

    private void ExpenseRecorderForm_Load(object sender, EventArgs e)
    {

    }

    private void tripSelect_SelectedIndexChanged(object sender, EventArgs e)
    {
        selectedExpense = (ExpenseItem)roster.ToFind((string)tripSelect.SelectedItem);
        listExpenses.Items.Add(selectedExpense);
    }


    private void listExpenses_SelectedIndexChanged(object sender, EventArgs e)
    {
        tripTextBox.Text = selectedExpense.Trip;
        tripTextBox.Enabled = false;
        descriptionTextBox.Text = selectedExpense.Description;
        amountTextBox.Text = selectedExpense.Amount.ToString();
        paymentMethodTextBox.Text = selectedExpense.PaymentMethod;
        dateExpenseTimePicker.Value = selectedExpense.Date;
        dateExpenseTimePicker.Enabled = true;
        noteTextBox.Text = selectedExpense.Note;
    }

Answer 1

I can’t code something like myVariable.Where(); since it’s not IEnumerable

I don’t really understand by what you mean with this.

As for the error, it says you can’t cast from the IEnumerable to ExpenseItem. You have to apply it like you final example like so and return the item rather than IEnumerable. I would just skip the Where clause and go straight into using FirstOrDefault

public ExpenseItem ToFind(string trip)
{
    return this.FirstOrDefault(e => e.Trip == trip);
}

I presume this is a custom made collection otherwise the Linq extensions won’t work on this

EDIT

If you really want this..

public IEnumerable<ExpenseItem> ToFind(string trip)
{
    return this.Where(e => e.Trip == trip);
}

Then you will need to deal with the list from the caller.

private void tripSelect_SelectedIndexChanged(object sender, EventArgs e)
{
    IEnumerable<ExpenseItem> selectedExpenses = roster.ToFind((string)tripSelect.SelectedItem);
    foreach(ExpenseItem item in selectedExpenses)
        listExpenses.Items.Add(item);
}