Loading comboBox from dataset - "Items collection cannot be modified when DataSource property is set"

Question

In my application, I have a model

public class LaborCategory
{
    public int Id { get; set; }

    [MaxLength(10)]
    public string Code { get; set; }

    [MaxLength(50)]
    public string Name { get; set; }
    public decimal Rate { get; set; }
    public decimal OnSite { get; set; }
    public decimal OffSite { get; set; }
}

I am wanting to create a comboBox (selectLaborCat) that has the first option as "Add New Labor Category" (this would be index 0) then the rest of the list where the selectLaborCat.Value = dataSet.Id and the selectLaborCat.Text = dataSet.Code

I THINK I am getting part of it correct by using

        var categories = _context.LaborCategories.OrderBy(c => c.Code).ToArray();

        selectLaborCat.DisplayMember = "Code";
        selectLaborCat.ValueMember = "Id";

        selectLaborCat.DataSource = categories;

as this renders the comboBox as I would expect.

But if I try a selectLaborCat.Items.Insert(0, "Add New Labor Category"); it errors out saying I cannot do Items collection cannot be modified when DataSource property is set

How can I get my "Add New Labor Category" in as index 0 ? I have tried adding the "Add New Category" in as a record in the data set, but I always want it to be index 0 of the comboBox, regardless of how I sort the dataset.

Am I forced to retrieve my dataset as a list, create a new list, add my default "Add New Category" as the first element, then copy the dataset list to the new list and bind the combo box to it like

        var categories = _context.LaborCategories.OrderBy(c => c.Code).ToList();
        var comboBoxElements = new List<LaborCategory>();

        var laborCategory = new LaborCategory();
        laborCategory.Id = 0;
        laborCategory.Code = "Add New Labor Category";
        comboBoxElements.Add(laborCategory);


        foreach (var category in categories)
        {
            comboBoxElements.Add(category);
        }

        selectLaborCat.DisplayMember = "Code";
        selectLaborCat.ValueMember = "Id";

        selectLaborCat.DataSource = comboBoxElements;

or is there a better way?

comboBoxElements.Add(new LaborCategory { Id = 0, Code = "Add New Labor Category" }); — Robert Harvey
If you want to keep your list ordered by code and display as first item a insertion prompt then you could simply try to add a prompt that is alphabetically lower than any other code. For example (Add new ....) — Steve

Sami Sami · Accepted Answer · 2016-10-31T22:11:19

Once you add a .DataSource to your listbox, you cannot modify the ListBox.Items collection i.e. after setting datasource to the ComboBox, Insert/Remove throws exception. A workaround can be, You can add the items to the ListBox directly instead of setting a DataSource. Then you'd be able to manipulate them directly.

If wanna go with setting DataSource, prepare your data-source, another option can be BindingList.

Futhermore, you can use a BindingList object:

Create a BindingList using your initial items as data Bind your
List item
listbox's data source to that BindingList object Add and remove items from the BindingList, and not from the listbox

Ref: Microsoft Link

Loading comboBox from dataset - "Items collection cannot be modified when DataSource property is set"

1 Answers