Hot-Link Menu in Right-Side Column

Wal Mart Online → Store Pickup → Free Shipping

Event Handler Code for AddToCart Button

All the groundwork should have been laid so we can now enter the code for the AddToCart Event Handler. Double-Click the AddToCart button and enter the following code:

'Event Handler for AddToCart Button on Order.aspx Web Page
Protected Sub btnAddToCart_Click(ByVal sender As Object, _
        ByVal e As EventArgs) Handles btnAddToCart.Click

    'Declare CartItem Class Variable (ItemToAdd)
    Dim ItemToAdd As New CartItem
    'Get Data About Selected Item
    ItemToAdd.SelectedItem = SelectedProduct

    'Determine Quantity Ordered
    ItemToAdd.Quantity = CInt(txtQuantity.Text)

    'Add Entry to Shopping Cart

    'Display Web Page: DisplayCart.aspx

End Sub

Well, we are getting closer, but, as you can see if we run the program, the ListBox on the DisplayCart page, isn't updating just yet. Enter the following sub which will display the shopping cart contents in the ListBox on the DisplayCart.aspx Web Page:

'Declare a Class Level Variable of the CartContents for all of the functions to access.
Private CartContents As SortedList

'Sub to Display Cart Contents to ListBox
Private Sub DisplayCart()

    'Clear the ListBox

    'Declare a CartItem Class Variable
    Dim CartEntry As CartItem

    'Display CartContents in ListBox
    For Each Item As DictionaryEntry In CartContents
        CartEntry = CType(Item.Value, CartItem)
End Sub

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The next function we will need is to pull the Current Shopping Cart contents out of Session State.

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 DisplayCart.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

And finally, to get the contents of the cart to display in the listbox on the DisplayCart web page enter the following code as the load page event handler:

'Load Page Event Handler, requests contents of shopping cart to be displayed
Private Sub DisplayCart_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

    'Pull the Cart Contents out of Session State
    CartContents = Me.GetCartContents

    'Display CartContents in the ListBox
    If Not IsPostBack Then
    End If

End Sub

Run the application, and add items to the cart, checking that the quantity increments correctly, as indicated in the diagram below:

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Shopping Cart Displaying Sample Items in VB.NET Web Program

Figure CC-24: Shopping Cart Displaying Sample Items on DisplayCart Web Page

If all goes well, the listing of the cart contents should be updating correctly in sync with the Add To Cart button. If not, cut and paste the code in the previous examples, as that code was used to generate the sample displayed on the screen.

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The preceding shopping cart was a retailers dream come true: You can keep adding items to the cart, but you can't take them away. Unfortunately, this may irritate customers to the point where they don't want to buy anything from you at all. So, I guess we are forced to include a Remove Item option, that is indicated by the Remove Button on the DisplayCart Web Page. Double-click the Remove Button to create the template for the remove button, and fill in the following code, which will remove the highlighted item from the Listbox:

Shopping Cart Remove Item Event Handler

'Event Handler for Remove Button to Remove Selected Item from ListBox
Protected Sub btnRemove_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btnRemove.Click

    'Check to see if Cart is Empty
    If CartContents.Count > 0 Then

        'Check to see if an item is selected to be deleted
        If lstCart.SelectedIndex > -1 Then

            'Remove the Selected Item
            'Tell the user to select something if they want it removed.
            lblMessage.Text="Please select the item you want to remove."
        End If
    End If
End Sub

Run the above code and place your favorite items in your cart. A typical cart with 3 items may look like the diagram below:

Example Shopping Cart Before Remove Item Operation

Figure CC-25: Example Shopping Cart Before Remove Item Operation

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Looking over the contents in my cart, and then reviewing my available capital for such a worthwhile expenditure, I notice that I am running a little short in my Halloween paraphenalia account. So, I guess I am going to have to do without those 4 severed hands, making this upcoming Halloween, a very bleak event, indeed. Unless, of course, some kind soul wishes to help out by clicking on some Google Ads, so I can puff that account back up. In the meantime, I have selected to place the Severed Heads item on the chopping block, prepared for the dreaded Remove Item event. Doing so gives the diagram illustrated below:

Example Shopping Cart After Remove Item Operation

Figure CC-26: Example Shopping Cart After Remove Item Operation

In order to continue with this guide, and begin the discussion on Emptying The Shopping Cart Press the Button below:

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