Question

General Problem:

I’m trying to create something similar to this:

The user can select a product from the dropdown, click add, and the result is another product
row being added underneath in the “Product Added” section. A “Product Descriptor” must be selected for each product that has been added via the dropdown in each row. Only when the user clicks the “Submit” button does each of the product rows get inserted to the database.

Question:

What is the best way to persist the product selections between Postbacks?

I’m not worried about persisting the “Product Descriptor” selections, I believe I can do that. My main concern is finding the best way of storing these temporary selections before they are saved to the database.

My current approach:

The way I’m doing it now is to manage list of ProductListItem objects in the viewstate. This list is bound to a ListView that displays the added products.

Private Property SelectedProductList As List(Of ProductListItem)
        Get
            Return CType(ViewState("SelectedProductList"), List(Of ProductListItem ))
        End Get
        Set(ByVal value As List(Of ProductListItem ))
            ViewState("SelectedProductList") = value
        End Set
End Property

The ProductListItem class:

<Serializable()>
Public Class ProductListItem

    Public Property ProductID As Integer
    Public Property ProductName As String

    ' ProductDescriptor class represents Product Descriptor (details omitted)
    Public Property Descriptor As ProductDescriptor 

    ' Constructor omitted

End Class

The Add Button Click handler:

 Protected Sub btnAddProduct_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnAddProduct.Click

        SelectedProductList.Add( New ProductListItem(...) )
        ProductListView.DataSource = SelectedProductList
        ProductListView.DataBind()

  End Sub

I’m thinking to use the Session instead of the Viewstate here, because I have two other similar situations on the same page, where I’m keeping lists of objects in the viewstate, and I’m worried about the Viewstate getting corrupted or getting too big. What do you think?

Thanks for your time!

Answer 1

The viewstate is the solution, because if you save them on the session you have this main problems:

• The session can be lost before the user press submit
• The user can open more than one windows with the same content, but the session will be the same, and a big mess will happens.

Now, on the viewstate to avoid to be too big you can do the following (all together):

• Compress it
• Split it.
• Optimize the what you write on it, eg you can write on there 100 records of DropDownList, or just the sql select that gets that 100 records.

You can also create a class that hold all the data together, optimize it, and save it on viewstate. On every page load, using this class you recreate the page form.

How to optimize class for viewstate

More on viewstate optimization:

Determine size of ASP.NET page's viewstate before serving page
http://www.codeproject.com/Articles/14733/ViewState-Compression
http://www.hanselman.com/blog/ZippingCompressingViewStateInASPNET.aspx
http://www.bloggingdeveloper.com/post/How-To-Compress-ViewState-in-ASPNET-20-ViewState-Compression-with-SystemIOCompression.aspx