Counter doesn't increment - asp.net

Question

Relatively new to coding, so there might be a clear mistake in the code. What I am trying to do is have a counter that increases by one each time a new product is added to the basket.
When the program is run, its default value is 0, when the you click on the first product to add to the basket, it increases to 1, however, if you add any more products it sticks at 1 instead of increasing each time.
I have included the code below - is there an obvious mistake I am over looking being a novice (I'll be the first to attempt that ha!). No error message is thrown at any point.
protected void BtnAddToBasket_Click(object sender, EventArgs e)
{
string ProductID = Convert.ToInt16((((Button)sender).CommandArgument)).ToString();
string ProductStock = "1";
DataListItem currentItem = (sender as Button).NamingContainer as DataListItem;
Label lblAvailableStock = currentItem.FindControl("lblAvailableStock") as Label;
if (Session["MyBasket"] != null)
{
DataTable dt = (DataTable)Session["My Basket"];
var checkProduct = dt.AsEnumerable().Where(r => r.Field<string>("ProductID") == ProductID);
if (checkProduct.Count() == 0)
{
string query = "SELECT * FROM Product WHERE ProductID = " + ProductID + "";
DataTable dtProduct = GetData(query);
DataRow dr = dt.NewRow();
dr["ProductID"] = ProductID;
dr["ProductName"] = Convert.ToString(dtProduct.Rows[0]["ProductName"]);
dr["ProductDescription"] = Convert.ToString(dtProduct.Rows[0]["ProductDescription"]);
dr["ProductPrice"] = Convert.ToString(dtProduct.Rows[0]["ProductPrice"]);
dr["ProductStock"] = ProductStock;
dr["ProductImageUrl"] = Convert.ToString(dtProduct.Rows[0]["ProductImageUrl"]);
dr["AvailableStock"] = lblAvailableStock;
dt.Rows.Add(dr);
Session["MyBasket"] = dt;
btnShoppingBasket.Text = dt.Rows.Count.ToString();
}
}
else
{
string query = "SELECT * FROM Product WHERE ProductID =" + ProductID + "";
DataTable dtProduct = GetData(query);
DataTable dt = new DataTable();
dt.Columns.Add("ProductID", typeof(string));
dt.Columns.Add("ProductName", typeof(string));
dt.Columns.Add("ProductDescription", typeof(string));
dt.Columns.Add("ProductPrice", typeof(string));
dt.Columns.Add("ProductStock", typeof(string));
dt.Columns.Add("ProductImageUrl", typeof(string));
dt.Columns.Add("AvailableStock", typeof(string));
DataRow dr = dt.NewRow();
dr["ProductID"] = ProductID;
dr["ProductName"] = Convert.ToString(dtProduct.Rows[0]["ProductName"]);
dr["ProductDescription"] = Convert.ToString(dtProduct.Rows[0]["ProductDescription"]);
dr["ProductPrice"] = Convert.ToString(dtProduct.Rows[0]["ProductPrice"]);
dr["ProductStock"] = ProductStock;
dr["ProductImageUrl"] = Convert.ToString(dtProduct.Rows[0]["ProductImageUrl"]);
dr["AvailableStock"] = lblAvailableStock;
dt.Rows.Add(dr);
Session["My Basket"] = dt;
btnShoppingBasket.Text = dt.Rows.Count.ToString();
}
}
Counter

Answer 1

From what I see it appears that you create new basket every time an item is added into the basket. The little mistake is that you use different names of saved basket entry in session:
if (Session["MyBasket"] != null)
This will be false first time so it goes into else block.
Session["My Basket"] = dt;
Here you store new DataTable with different key. So the next time the if statement will still be false. So just make sure that the name is consistent. "MyBasket" != "My Basket"

Answer 2

Fixed where "MyBasket" was "My Basket"; reduced code duplication. The misspelling is a compelling reason to use constants instead of string literals.
protected void BtnAddToBasket_Click(object sender, EventArgs e)
{
string ProductID = Convert.ToInt16((((Button)sender).CommandArgument)).ToString();
string ProductStock = "1";
DataListItem currentItem = (sender as Button).NamingContainer as DataListItem;
Label lblAvailableStock = currentItem.FindControl("lblAvailableStock") as Label;
if (Session["MyBasket"] == null)
{
DataTable dt = new DataTable();
dt.Columns.Add("ProductID", typeof(string));
dt.Columns.Add("ProductName", typeof(string));
dt.Columns.Add("ProductDescription", typeof(string));
dt.Columns.Add("ProductPrice", typeof(string));
dt.Columns.Add("ProductStock", typeof(string));
dt.Columns.Add("ProductImageUrl", typeof(string));
dt.Columns.Add("AvailableStock", typeof(string));
}
DataTable dt = (DataTable)Session["MyBasket"];
var checkProduct = dt.AsEnumerable().Where(r => r.Field<string>("ProductID") == ProductID);
if (checkProduct.Count() == 0)
{
string query = "SELECT * FROM Product WHERE ProductID = " + ProductID + "";
DataTable dtProduct = GetData(query);
DataRow dr = dt.NewRow();
dr["ProductID"] = ProductID;
dr["ProductName"] = Convert.ToString(dtProduct.Rows[0]["ProductName"]);
dr["ProductDescription"] = Convert.ToString(dtProduct.Rows[0]["ProductDescription"]);
dr["ProductPrice"] = Convert.ToString(dtProduct.Rows[0]["ProductPrice"]);
dr["ProductStock"] = ProductStock;
dr["ProductImageUrl"] = Convert.ToString(dtProduct.Rows[0]["ProductImageUrl"]);
dr["AvailableStock"] = lblAvailableStock;
dt.Rows.Add(dr);
Session["MyBasket"] = dt;
btnShoppingBasket.Text = dt.Rows.Count.ToString();
}
}