c# how to avoid adding the same product id from textbox.text to listbox

Question

I have a code here that tells you that, for every product in a bound list called product of a ProductListSource.DataSource , I have an if statement that if the product.ProdID is equal to the text you have inputted, you should add that on to a listbox. But the problem is I want a limiter... I don't want the same id to be added more than one. Here's my code demonstrating what I have done so far:

private void AddToCartButton_Click(object sender, EventArgs e)
{
    foreach (var product in (BindingList<Product>) ProductListSource.DataSource)
    {
        if (product.ProdID == ProdIDText.Text.Trim())
        {
            CartList.Items.Add(product);
        }
    }
}

Answer 1

You can use the Distinct LINQ extension method to filter products with common product IDs:

var productList = (BindingList<Product>)ProductListSource.DataSource;
foreach (var product in productList.Distinct((one, two) => one.ProdID == two.ProdID)) 
{
    if (product.ProdID == ProdIDText.Text.Trim())
    {
        CartList.Items.Add(product);
    }
}