Hey I recently created a shopping cart but I'm having problems sorting the purchased items into a gridview. this is my cart class:
Public Class Cart
Private dt As DataTable = New DataTable()
Public Sub New()
dt.Columns.Add(New DataColumn("Product ID"))
dt.Columns.Add(New DataColumn("Quantity"))
dt.PrimaryKey = New DataColumn() {dt.Columns("Product ID")}
End Sub
Public Sub AddToCart(ByVal prd_id As Integer, ByVal quantity As Integer)
Dim dr As DataRow = dt.NewRow()
dr("Product ID") = prd_id
dr("Quantity") = quantity
dt.Rows.Add(dr)
End Sub
Public Sub RemoveFromCart(ByVal prd_id As Integer)
Dim dr As DataRow = dt.Rows.Find(prd_id)
dt.Rows.Remove(dr)
End Sub
Public Function GetCart() As DataTable
Return dt
End Function
End Class
This is the button function:
If Session("Customer_ID") <> Nothing Then
Dim userCart As Cart = CType(Session("shoppingCart"), Cart)
Dim qty As Integer = txtqty.text
Dim pid As Integer = lblid.text
userCart.AddToCart(pID, qty)
Else
Response.Redirect("User_Login.aspx")
End If
When I try to run the code I get an error saying that ("Object reference not set to an instance of an object.") please help I've completely ran out of ideas. how can i fix this?
The Session Key of "shoppingCart" has a value Nothing, so when you try to call the AddToCart function from your userCart instance you receive this error. You must ensure that Session("shoppingCart") is not nothing. If it is you should create it or perform the logic you wish to perform in that scenario. Note that Sessions will time out after a client is inactive for a certain amount of time (configurable in the Web.config file), so this is a very real scenario.
Dim userCart As Cart = Nothing
If Not Session("shoppingCart") Is Nothing Then
userCart = CType(Session("shoppingCart"), Cart)
Else
userCart = New Cart
End If
userCart.AddToCart(pID, qty)
Don't forget to save your cart to the Session!
Session("shoppingCart") = userCart
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