Listbox in asp.net not getting selected items

问题:

I have multiple dropdown & listbox in my webpage.

I am trying to get a list of CategoryID from a lstCatID listbox i am able to populate the listbox with category name.

If i remember correctly in first attempt my code worked fine, after that i made some change then it stated to always get the first item selected x No. of time

<asp:ListBox ID="lstCatID" runat="server" DataTextField="CategoryName" 
                DataValueField="CategoryID" SelectionMode="Multiple" CssClass="lstListBox">
 </asp:ListBox>



protected void Button1_Click(object sender, EventArgs e)
{
    string CatID = string.Empty;
    foreach (ListItem li in lstCatID.Items)
    {
        if (li.Selected == true)
        {
           // Response.Write();
            CatID += lstCatID.SelectedItem.Value + ",";
        }
    }
    Response.Write(CatID);
}

I am not sure what is going wrong i checkd MSDN it show exactly the same way of doing it.

May be i am doing something wrong.

Just to add using firefox i am able to see multiple selected value have selected property.

<option value="3" selected="selected">One</option>
<option value="2">Two</option>
<option value="29" selected="selected">Three</option>
<option value="25" selected="selected">Four</option>
<option value="22" >Five</option>

My output in this case will be 3,3,3

I would appreciate help in this regard

回答1:

You are setting it to the same value every time:

foreach (ListItem li in lstCatID.Items)
{
    if (li.Selected == true)
    {
       // you are always using lstCatID.SelectedItem.Value.
        CatID += lstCatID.SelectedItem.Value + ",";
    }
}

When you actually want the value of the item in your loop that is selected:

foreach (ListItem li in lstCatID.Items)
{
    if (li.Selected == true)
    {
        // get the value of the item in your loop
        CatID += li.Value + ",";
    }
}

回答2:

I am not sure what is wrong with the logic i am using.

I came across a nice solution using LINQ.

This single statement works great & gets me the desired results.

string values = String.Join(", ", lstCatID.Items.Cast<ListItem>().Where(i => i.Selected).Select(i => i.Value).ToArray());

RESULT: 3,29,25

回答3:

Try to add Page.IsPostback on your Page_Load like

protected void Page_Load(object sender, EventArgs e)
{
    // Do your API code here unless you want it to occur only the first
    // time the page loads, in which case put it in the IF statement below.
    if (!Page.IsPostBack)
    {

    }
}

Code:

protected void Button1_Click(object sender, EventArgs e)
{
    string CatID = string.Empty;
    foreach (ListItem li in lstCatID.Items)
    {
        if (li.Selected )
        {
           // TODO: Whatever you are doing with a selected item.
        }
    }
    Response.Write(CatID);
}

Once i was facing the same problem and i made Postback mistake.

Hope it works.

回答4:

Get the selected items using linq

var selected = lstCatID.Items.Where(i => i.Selected);

回答5:

Minutes later I found a solution:

If lstLocations.Items.Count > 0 Then
            For i As Integer = 0 To lstLocations.Items.Count - 1
                If lstLocations.Items(i).Selected Then
                    'insert command
                    Dim selectedItem As String = lstLocations.Items(i).Text
                End If
            Next
        End If

This worked fine in my scenario