VB.Net Check if a checkbox list item is checked/unchecked

Question

I have a checkbox list which is filled with entries from my database on page load. I need to update an entry in my database when a item is checked and when an item is unchecked. Right now I am doing the following:

<asp:CheckBoxList id="check1" AutoPostBack="True" TextAlign="Right" OnSelectedIndexChanged="Check" runat="server">

</asp:CheckBoxList>

And the function:

Sub Check(ByVal sender As Object, ByVal e As EventArgs)
    Dim sql As String
    If check1.SelectedItem.Selected = True Then
        sql = "UPDATE Customer SET unauthorized = 'True' WHERE ID = @ID"
        db.execUpdateQuery(sql, New SqlClient.SqlParameter("@ID", check1.SelectedItem.Value))
    Else
        sql = "UPDATE Customer SET unauthorized = 'False' WHERE ID = @ID"
        db.execUpdateQuery(sql, New SqlClient.SqlParameter("@ID", check1.SelectedItem.Value))
    End If
End Sub

But when I uncheck a button the else case is never ran. Also, if I have 4 buttons checked and I uncheck all four buttons, when I uncheck the fourth button I get an error at the line:

If check1.SelectedItem.Selected = True Then

The error is: "Object reference not set to an instance of an object."

Is there a better way to check if a list item is checked or unchecked?

Thanks

With old school HTML unchecked checkboxes don't return values to the server...maybe that's what you're running into here? With nothing checked there would be no SelectedItem in your checkboxlist. — Tim
– Tim, Commented May 14, 2012 at 17:27
Shouldn't you be basing this on ItemCheck and not SelectedIndexChange? — APrough
– APrough, Commented May 14, 2012 at 17:28

Romil Kumar Jain · Accepted Answer · 2012-05-14 18:03:34Z

1

for (int i = 0; i < check1.Items.Count; i++)
  if (check1.GetItemChecked(i))
    // Do selected stuff
  else
    // Do unselected stuff

If the the check is in indeterminate state, this will still return true. You may want to replace

if (check1.GetItemChecked(i))

with

if (check1.GetItemCheckState(i) == CheckState.Checked)

if you want to only include actually checked items.

edited May 14, 2012 at 18:03

answered May 14, 2012 at 17:30

Romil Kumar Jain

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7 Comments

ewein Over a year ago

Is there anyway to avoid the use of a for loop?

Yatrix Over a year ago

@ewein Why do you want to avoid a For loop?

ewein Over a year ago

its not very efficient to loop through each item and do a database update on each iteration.

ewein Over a year ago

I just need something that allows me to get the item that was checked or unchecked then I can do a single update.

Romil Kumar Jain Over a year ago

Now check the modified answer. clbIncludes was the check box list.

|

user3972104 · Accepted Answer · 2014-10-29 11:49:22Z

1

You can try this also

   For i As Integer = 0 To CheckedListBox1.Items.Count - 1
        If CheckedListBox1.GetItemChecked(i) = True Then
            sql = "UPDATE Customer SET unauthorized = 'True' WHERE ID = @ID"
            db.execUpdateQuery(sql, New SqlClient.SqlParameter("@ID", check1.SelectedItem.Value))
        Else
            sql = "UPDATE Customer SET unauthorized = 'False' WHERE ID = @ID"
            db.execUpdateQuery(sql, New SqlClient.SqlParameter("@ID", check1.SelectedItem.Value))  
        End If
    Next

answered Oct 29, 2014 at 11:49

user3972104

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