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Add CartItem Class

The next step is to add the CartItem class. In case you've forgotten how to add a class, you can review how we created the Product Class. In a similar, or even the exact same, manner, create the CartItem Class with the code below:

Imports Microsoft.VisualBasic

Public Class CartItem
    Public SelectedItem As Product
    Public Quantity As Integer

    Public Function Display() As String
        Return SelectedItem.Name & " (" &Quantity.ToString() & " at " _
            & FormatCurrency(SelectedItem.UnitPrice) & " each)"
    End Function
End Class

After the above code is entered, and you have set Order.aspx.vb as the start page, run the program, to make sure everything is still good. Although, we have entered the class, since we aren't using it, it should have no effect yet. Change the selected product to Hippie and the screen you should be seeing is:

Figure CC-22: Change Selected Product to Hippie

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Add Ons Desktops Net Books Laptops PDA Mac Gaming Products Nintendo Gaming Products PC Gaming Products Play Station 3 Games Sony PSP Gaming Products Wii Gaming Products Xbox Gaming Products Accessories Blue Tooth Car Electronics Cell Phones & Service GPS Devices Home Theater Marine Electronics Mobile Broadband Office Products Photography Products Precision Measurement Security Products Video Products Business Software Graphics Software Mac Software Multimedia Networking Software Operating Systems Programming Software Security Software Utilities Web Development Apple Computer Books Certification Books Business Books Database Books Computer Hardware Computer Networking Computer Programming Computer Science Computer Security Digital Music Digital Photography Game Strategy Books General Computer Graphics Design Microsoft Computing Mobile Wireless Operating Systems Science Books Technical Books Web Development

Next, we will set the PostBackUrl property of the Continue Shopping button on the DisplayCart page, so that it jumps back to the order page. Performing a Single-Click on the ContinueShopping button will bring up the Properties Page somewhere on your screen. Left-Click on the values column of the PostBackUrl property on the btnContinue properties page as indicated in the diagram below:

Figure CC-23: Select PostBackUrl Property of Continue Shopping Button

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Press the Select Url button to the right of the PostBackUrl Value Column (right where the arrow is pointing), to bring up the Select URL dialog box as indicated in the diagram below:

Figure CC-23: Select PostBackUrl Dialog Box

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Switch back to the Design View page for Orders.aspx and change the PostBackUrl on the Go To Cart button to jump to the DisplayCart page, like we just did for the Continue Shopping button in the example above. Completing a circuit where we can freely navigate between the pages.

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Once you have divested yourself of all that unnecessary disposable capital @ Centurion Online, come back and run the program jumping between the pages using the Go To Cart and Continue Shopping buttons.

Create GetCartContents Function Using Session State

A function to return the Cart Contents is needed. For this application, we will use SessionState to hold the contents of the cart. Enter the following function in the Order.aspx.vb module:

'Function to return the contents of the shopping cart held in session state
Private Function GetCartContents() As SortedList

    'Create a variable to hold the session name so it will be insertedable by Intellisense.
    Dim SessionName As String = "Cart"

    'If no shopping cart exists yet, create one.
    If Session(SessionName) Is Nothing Then
        Session.Add(SessionName, New SortedList)
    End If

    'Convert Session Variable to SortedList Data Type and return
    Return CType (Session(SessionName), SortedList)
End Function

It is good practice to run the code as you add the functions, just to make sure you aren't making any fatal errors along the way. Run the program, and change a few selections, to make sure you haven't lost functionality as we proceed. I try to add new functions, so that as I add them, the code still functions, which means entering code at the lowest level first, then working your way up.

The next code snippet we need to add is a Sub to add an individual item to the Users Shopping Cart. Enter the code below to process adding an item to the cart:

'Sub to add selected item to the Current Shopping Cart Contents
Private Sub AddToCart(ByVal ItemToAdd As CartItem)

    'Create a SortedList container for the selected item.
    Dim CurrentCartContents As SortedList

    'Create a String to Hold the Product ID
    Dim ProductCode As String

    'Call Function to Place Selected Item in SortedList Data Type
    CurrentCartContents = Me.GetCartContents

    'Get The ProductID to use as a key
    ProductCode = SelectedProduct.ProductID

    'Check to see if item is already in Cart
    If CurrentCartContents.ContainsKey(ProductCode) Then
        ItemToAdd = CType(CurrentCartContents(ProductCode), CartItem)
        ItemToAdd.Quantity += CInto(txtQuantity.Text)
    Else
        CurrentCartContents.Add(ProductCode, ItemToAdd)
    End If
End Sub

If you would like like to see a shopping cart in action, so you can see where we are headed with this, take a visit to:

Wal Mart Online → Store Pickup → Free Shipping

In order to continue with this guide, and continue the discussion on Adding the Shopping Cart Class Press the Button below:

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