Question

I have a LINQ query that retrieves rows from a dataset and binds it to a Winforms combobox:

namespace KimHongAutoAccessory.Forms
{
    public partial class EngineFilter : Form
    {
        public EngineFilter()
        {
            InitializeComponent();
        }

        private void btnCancel_Click(object sender, EventArgs e)
        {
            this.Close();
        }

        private void EngineFilter_Load(object sender, EventArgs e)
        {

            this.engineFilterTableAdapter.Fill(this.manufacturerEngine.EngineFilter);

            var manufacturers = (from m in manufacturerEngine.EngineFilter
                                 select new { m.ManufacturerID, m.Manufacturer })
                                 .Distinct().ToList();

            cboManufacturerFilter.DataSource = manufacturers.ToArray();
            cboManufacturerFilter.DisplayMember = "Manufacturer";
            cboManufacturerFilter.ValueMember = "ManufacturerID";


        }
    }
}

But I want to add a union item to the combobox like the word “[All]”:

|-------|
|TOYOTA |
|-------|
|KUBOTA |
|-------|
|FORD   |
|-------|
|[All]  |
|-------|

Can anybody give me a trick?

Answer 1

Presumably your “(All)” item would have a special value for its ID so you know when it has been selected. Let’s assume its ID is -1.

var manufacturers = (from m in manufacturerEngine.EngineFilter
                     select new { m.ManufacturerID, m.Manufacturer }
                    ).Distinct().ToList();

manufactorers.Add(new { ManufacturerID = -1, Manufacturer = "(All)" });

cboManufacturerFilter.DataSource = manufacturers.ToArray();
// ... etc ...