Cannot retrieve the values from multiple selection in 1 Listbox VB.net

Question

I want to retrieve the values of the current selected items in the listbox and whenever the user pick more items,the sum of price of these items will be displayed in a Label ex: the user picks 2 phone names from the listbox and the sum of their price will be displayed in the label (It is working for only the first item the user chooses but ignores everything else selected and it doen't work when the user select an item it only displays the price when i press a button) ,Here is what i tried :

Partial Class PickItems
Inherits System.Web.UI.Page

Dim sum As Integer = 0
Protected Sub ListBox1_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ListBox1.SelectedIndexChanged

    sum = sum + CInt(ListBox1.SelectedValue)
    Label1.Text = sum.ToString()


End Sub

Protected Sub Page_Load(sender As Object, e As EventArgs) Handles Me.Load
    Label2.Text = Request.QueryString("Name").ToString()


End Sub End Class

Here is the Listbox code <asp:ListBox ID="ListBox1" runat="server" SelectionMode="Multiple" DataSourceID="SqlDataSource1" DataTextField="PhoneName" DataValueField="PhonePrice"></asp:ListBox>

And here is how the page looks like: I will also need to move the selected items from this page to the next page(same as i did with the Request.QueryString("Name....) Any help will be appreciated!

Sage Pourpre · Accepted Answer · 2016-05-22 21:24:19Z

1

If you want a sum, you need to loop into each of the selected indices to calculate the sum.

Private Sub ListBox1_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ListBox1.SelectedIndexChanged
    sum = 0 'reset sum to 0
    For Each I As Integer In ListBox1.GetSelectedIndices
        Dim CurrentItem As ListItem = ListBox1.Items(I)
        sum += CInt(CurrentItem.Value) 
    Next
End Sub

Please note that for the SelectedIndexChanged event to work, you will need to set the AutoPostback attribute to true for your listbox.

AutoPostBack="True"

edited May 22, 2016 at 21:24

answered May 22, 2016 at 20:11

Sage Pourpre

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5 Comments

xTMx Over a year ago

I added 'Label1.Text = sum' after Next but the sum is 0 whatever item is chosen...How can i get it to show the correct sum?

xTMx Over a year ago

i also added the code to onclick button event because the selectedindexchanged is not working and updating the label,only pressing the button will show the sum in Label1.

Sage Pourpre Over a year ago

If you want it to execute when listbox selection is changed, you need to add AutoPostBack="True" in your listbox code so the event is called. Otherwise, SelectedIndexChanged is not called.

xTMx Over a year ago

True but the page will refresh when i click on any item now ,so i can't choose more than 1 item.

Sage Pourpre Over a year ago

The page refresh but you do not loose selected items and can therefore select multiples one. The more clean way to do it would be to use webapi request to the server than update the value with Javascript. That way, you avoid a page refresh and a button click and you get the updated value to your label. That is the way I would go. You can see an example here: techfunda.com/howto/304/update-record-using-web-api

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