Select multiple value in ListBox using ASP.NET and C#

Question

Why "SelectedValue" selects only the first value in my multiple selection mode ?

<dt>Tags:</dt><dd>
<asp:ListBox ID="ListTag" runat="server" SelectionMode="Multiple"
    DataSourceID="SqlDataSourceTag" DataTextField="tag_name" 
    DataValueField="tag_id">
</asp:ListBox>
<asp:SqlDataSource ID="SqlDataSourceTag" runat="server" 
    ConnectionString="<%$ ConnectionStrings:db_cc %>">
</asp:SqlDataSource>
</dd>

ListTag.SelectedValue = "Tag1"; <-- only this is selects
ListTag.SelectedValue = "Tag2";

SelectedValue represents only single value that's why you get first selected value. If you want to get all the selected value you need to iterate thru the items of list and check Selected property of each item and get the Value of it if it's true. — Chetan
– Chetan, Commented Feb 26, 2018 at 10:38

ThaNet · Accepted Answer · 2018-02-26 14:41:12Z

2

in your asp page you have this.

<asp:ListBox ID="ListTag"  runat="server" AutoPostBack="True" SelectionMode="Multiple" Width="250px">
    <asp:ListItem Selected="False" Text="Tag-1" Value="1">Tag - 1</asp:ListItem>
    <asp:ListItem Selected="False" Text="Tag-2" Value="2">Tag - 2</asp:ListItem>
    <asp:ListItem Selected="False" Text="Tag-3" Value="3">Tag - 3</asp:ListItem>
    <asp:ListItem Selected="False" Text="Tag-4" Value="4">Tag - 4</asp:ListItem>
    <asp:ListItem Selected="False" Text="Tag-5" Value="5">Tag - 5</asp:ListItem>
    <asp:ListItem Selected="False" Text="Tag-6" Value="6">Tag - 6</asp:ListItem>
    <asp:ListItem Selected="False" Text="Tag-7" Value="7">Tag - 7</asp:ListItem>
    <asp:ListItem Selected="False" Text="Tag-8" Value="8">Tag - 8</asp:ListItem>
    <asp:ListItem Selected="False" Text="Tag-9" Value="9">Tag - 9</asp:ListItem>
    <asp:ListItem Selected="False" Text="Tag-10" Value="10">Tag - 10</asp:ListItem>
</asp:ListBox>

then in your cs(Code Behind) in the event that you want you have this.

  for (int i = 0; i < lsBox.Items.Count; i++)
        {
            var item = lsBox.Items[i];
            string[] selectecvalues = new string[] { "1", "3", "6", "9" };

            if (selectecvalues.Contains(item.Value)) // or item.Text  if you like
            {
                lsBox.Items[i].Selected = true;
            }
        }

that will result in Tags 1,3,6,9 selectd

edited Feb 26, 2018 at 14:41

answered Feb 26, 2018 at 10:43

ThaNet

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5 Comments

Daniel Over a year ago

It does not work. I have to programmatically select several tags. There is no need to check is some options are selected.

Daniel Over a year ago

I dont't have method,,SetSelected'' in ListTag

Daniel Over a year ago

I have ListTag.Items.Count = 0 so I can't looping for this, but I have options tags with multiple choices

ThaNet Over a year ago

@Daniel you need to load the data before, called the looping

Daniel Over a year ago

Thanks @ThaNet I I forgot to add ListTag.DataBind(); :)

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