How to check whether an item exists in a ListBox in asp.net

asp.net listbox.items.contains
The following asp.net c# example code demonstrate us how can we determine whether a ListItem object contains in the ListBox items collection.

Collection<T> Class Contains() method determines whether an element is in the collection. So we can search for the specified ListItem object from ListBox list items collection by using Contains() method. Contains() method return a Boolean value. It returns True if the specified object is found; otherwise the method return False. Contains() method implements as ICollection<T>.Contains(T).
listbox-items-contains.aspx

<%@ Page Language="C#" AutoEventWireup="true"%>    
      
<!DOCTYPE html>
        
<script runat="server">
    protected void Page_Load(object sender, EventArgs e)
    { 
        if(!Page.IsPostBack)
        {
            string[] birds = { 
                                 "Golden Oriole",
                                 "Yellow Oriole",
                                 "Orchard Oriole",
                                 "Northern Oriole",
                                 "Cowbird",
                                 "African Black-headed Oriole"
                             };

            ListBox1.DataSource = birds;
            ListBox1.DataBind();

            ListBox1.Rows = ListBox1.Items.Count;
        }
    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        ListItem litem = new ListItem("Cowbird","Cowbird");
        if (ListBox1.Items.Contains(litem))
        {
            Label1.Text = "item found: " + litem.Text + " | " + litem.Value;
        }
        else
        {
            Label1.Text = "not found";
        }
    }
</script>        
        
<html xmlns="http://www.w3.org/1999/xhtml">        
<head id="Head1" runat="server">        
    <title>asp.net listbox.items.contains</title>  
</head>        
<body>        
    <form id="form1" runat="server">        
    <div>        
        <h2 style="color:MidnightBlue; font-style:italic;">        
            asp.net example - listbox.items.contains
        </h2>        
        <hr width="550" align="left" color="Gainsboro" />        
        <asp:Label       
            ID="Label1"       
            runat="server"      
            Text="select item(s) from listbox."
            Font-Size="X-Large"
            Width="350"
            >      
        </asp:Label>      
        <br /><br />  
        <asp:ListBox  
            ID="ListBox1"  
            runat="server"  
            AutoPostBack="true"  
            Font-Size="X-Large"
            SelectionMode="Multiple"
            Font-Names="Comic Sans MS"
            >  
        </asp:ListBox> 
        <br /><br />
        <asp:Button   
            ID="Button1"   
            runat="server"   
            Text="ListBox Contains Item 'Cowbird'?"  
            OnClick="Button1_Click"
            Height="40"  
            Font-Bold="true"  
            />  
    </div>        
    </form>        
</body>        
</html>
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