带有SelectedIndex和Value的Listbox Bug？

Question

I think I found a bug in the use of the Listbox. Example: ListBox with Editbutton which loads it into special fields:

The listbox has 4 Items:

1. PhoneNumber: +15454545 (Value 2)(Index 0)
2. Email: Test@testmail.com (Value 1)(Index 1)
3. FaxNumber: +1515515151 (Value 3)(Index 2)
4. Email: Test2@testmail.com (Value 1)(Index 3)

Then the editbuttoncode:

protected void EditKOFC(object sender, EventArgs e)
    {
        try
        {
            if (ListBoxKOFC.SelectedItem == null)
            {
                LabelMPE.Text = "Please select first!";
                ModalPopupExtender1.Show();
            }
            else
            {

                string value = ListBoxKOFC.SelectedValue;
                Session["EditID"] = ListBoxKOFC.SelectedIndex;
                string[] meineStrings = ListBoxKOFC.SelectedItem.Text.Split(new Char[] { ':' });
                string text = meineStrings[1];
                string text2 = text.Substring(1);
                TextBoxKOFC.Text = text2;

                foreach (ListItem item in DropDownListKOFC.Items)
                {
                    item.Selected = false;
                    if (item.Value == value)
                    {
                        item.Selected = true;
                    }
                }
                editing = true;
                AddKOFC.Text = "Save";
            }
        }
        catch (Exception ex)
        {
            GlobalFunctions.Error_Log(ex, ex.TargetSite.ToString());
        }
    }

And there I get the Problem. When I select the first three items, its all fine. When I select the 4th item, it uses all the data from the second one, even if they have different Indexes!

Does Value affect the Index here, and if yes, why ?! Its really a problem for me, because i need to store the contacttype in the Value. (1= Email, 2 = Phone etc);

Thanks allready!

Edit: To clarify: The Edit-Button is a Button itself outside the ListBox.

<asp:TableRow>
            <asp:TableCell>
                <asp:UpdatePanel runat="server" UpdateMode="Conditional" ID="UpdatePanel2">
                    <Triggers>
                        <asp:AsyncPostBackTrigger ControlID="AddKOFC" EventName="Click" />
                    </Triggers>
                    <ContentTemplate>
                        <asp:DropDownList runat="server" ID="DropDownListKOFC" />
                    </ContentTemplate>
                </asp:UpdatePanel>
            </asp:TableCell>
            <asp:TableCell>
                <asp:UpdatePanel runat="server" UpdateMode="Conditional" ID="UpdatePanel1">
                    <Triggers>
                        <asp:AsyncPostBackTrigger ControlID="AddKOFC" EventName="Click" />
                    </Triggers>
                    <ContentTemplate>
                        <asp:TextBox runat="server" ID="TextBoxKOFC" />
                    </ContentTemplate>
                </asp:UpdatePanel>
            </asp:TableCell><asp:TableCell>
                <asp:UpdatePanel runat="server" UpdateMode="Conditional" ID="UP2">
                    <ContentTemplate>
                        <asp:Button runat="server" ID="AddKOFC" OnClick="AddContactInformation" Text="Add Contactinformation" />
                        <asp:HiddenField ID="HFAdd" runat="server" />
                        <ajaxToolkit:ModalPopupExtender ID="ModalPopupExtender1" runat="server" BackgroundCssClass="modalBackground"
                            TargetControlID="HFAdd" PopupControlID="PanelChoose" BehaviorID="MPEchoose">
                        </ajaxToolkit:ModalPopupExtender>
                        <asp:Panel ID="PanelChoose" runat="server" BorderStyle="Solid" BackColor="ButtonShadow">
                            <asp:Label ID="LabelMPE" runat="server"></asp:Label>
                            <asp:Table ID="Table3" runat="server">
                                <asp:TableRow>
                                    <asp:TableCell>
                                        <asp:Button ID="ButtonOK" runat="server" Text="Ok" />
                                    </asp:TableCell>
                                </asp:TableRow>
                            </asp:Table>
                        </asp:Panel>
                    </ContentTemplate>
                    <Triggers>
                        <asp:AsyncPostBackTrigger ControlID="AddKOFC" EventName="Click" />
                        <asp:AsyncPostBackTrigger ControlID="ButtonOK" EventName="Click" />
                    </Triggers>
                </asp:UpdatePanel>
            </asp:TableCell></asp:TableRow>
        <asp:TableRow>
            <asp:TableCell>
                <asp:Label ID="Label13" runat="server"></asp:Label>
            </asp:TableCell></asp:TableRow>
        <asp:TableRow>
            <asp:TableCell>
                <asp:UpdatePanel runat="server" UpdateMode="Conditional" ID="UP3">
                    <Triggers>
                        <asp:AsyncPostBackTrigger ControlID="AddKOFC" EventName="Click" />
                    </Triggers>
                    <ContentTemplate>
                        <asp:ListBox runat="server" ID="ListBoxKOFC" ToolTip="The way to contact this person">
                        </asp:ListBox>
                    </ContentTemplate>
                </asp:UpdatePanel>
            </asp:TableCell><asp:TableCell>
                <asp:Button ID="ButtonUpdate" runat="server" Text="Edit" OnClick="EditKOFC" />
            </asp:TableCell><asp:TableCell>
                <asp:Button ID="ButtonDelete" runat="server" Text="Delete" OnClick="DeleteKOFC" />
            </asp:TableCell></asp:TableRow>
        <asp:TableRow>

Edit2 for more clarification(or whatever):

This is how it looks. Then i want to edit the 4th item:

And when I debug:

The 4th Item is not selected ... even if you see in the picture befor, it is!!

If I look at the ListBoxKOFC itself:

And when the code is done, the wrong item got selected and loaded to edit:

But as you can see in the 4. Screenshot -> The index of the item i want to edit is three. Only the value is the same. But WHY cant the value be the same, the index is another allways ...

Does the Value work as Index here ?! (Cant be, but atm im not sure anymore ...) Or is the Value just bugged ?

Answer 1

Yep. Your problem is having two items with the same Value. The ASP.Net dropdown renders to the browser as a standard HTML select control, with the form:

<select name="cars">
<option value="volvo">Volvo</option>
<option value="saab">Saab</option>
<option value="fiat">Fiat</option>
<option value="audi">Audi</option>
</select>

http://www.w3schools.com/html/tryit.asp?filename=tryhtml_select2

Each option is supposed to have a unique value.

Remember that when the postback happens, the ASP.Net engine creates a new instance of your page and applies the view state that came in with the request. When it tries to re-create your dropdown control, it searches for an option with the correct value and stops when it finds one.

Answer 2

I think I once had this problem before. It turned out that you cannot set ListBox sort property to true; otherwise the index will be useless.

But this might not be your case.

Answer 3

First of all, you should not have 2 item with same value in a list box. If you must have duplicate value then you can't use value as condition.

Asp .Net does not treat the Value work as Index. It is your code that use value as condition which is wrong(refer below).

if (item.Value == value)
{
    item.Selected = true;
}

Solution: You need to use index as your condition. Try below code:

for (int i = 0; i < DropDownListKOFC.Items.Count; i++)
{
    DropDownListKOFC.Items[i].Selected = false;

    if (i == ListBoxKOFC.SelectedIndex)
    {
      DropDownListKOFC.Items[i].Selected = true;
    }
}

Answer 4

Thanks to the others for helping me to understand the problem! I will just share my little workarround, maybe it will help someone!

Add a random value to the current value while you load it:

Random rnd = new Random();
int random = rnd.Next(1,1000000);

Then add it togheter with the value:

ListItem listitem = new ListItem(text, value + random.ToString(), true);
ListBox.Items.Add(listitem);

And if you need it, just use substring:

string value = ListBox.SelectedValue;
value = value.Substring(0, 1);

But this will only work if you have allways the same number of numbers infront of the random.