Introduction
Various methods is available to validate the TextBox but very few methods is available to validate the Dropdownlist. Here i have two methods to validate it. In the first method i will use RequiredFieldValidator control with InitialValue property, in the second method i will use javaScript. for validation.
I-Method
In the first method, first to add some items in the dropdownlist. Now, take a RequiredFieldValidator control to validate the Dropdownlist. Set some required properties of validator control. These are:ControlToValidate="Id of Dropdownlist control"
ErrorMessage=" Please select item from Dropdownlist "
InitialValue = "Match with Text item which is available in Dropdownlist also you do not want to display. Like
<asp:ListItem>select one</asp:ListItem>
<asp:ListItem>Apple </asp:ListItem>
<asp:ListItem>Mango</asp:ListItem>
<asp:ListItem>Orange</asp:ListItem>
Here, i set the InitialValue = select one.
Complete code to describe more:
<%@ Page Language="C#" %>
<!DOCTYPE html>
<script runat="server">
protected void Button1_Click(object sender, EventArgs e)
{
Label1.Text += "Your selected item is <br/>"+DropDownList1.SelectedItem.Text;
}
protected void Page_Load(object sender, EventArgs e)
{
}
</script>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:DropDownList ID="DropDownList1" runat="server" Height="30px" Width="149px" AutoPostBack="True">
<asp:ListItem Selected="True">select one</asp:ListItem>
<asp:ListItem>Apple </asp:ListItem>
<asp:ListItem>Mango</asp:ListItem>
<asp:ListItem>Orange</asp:ListItem>
</asp:DropDownList>
<br />
</div>
<asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" ControlToValidate="DropDownList1" ErrorMessage="RequiredFieldValidator" InitialValue="select one">Please Select Item</asp:RequiredFieldValidator>
<asp:Button ID="Button1" runat="server" OnClick="Button1_Click" Text="Button" />
<br />
<asp:Label ID="Label1" runat="server"></asp:Label>
</form>
</body>
</html>
<!DOCTYPE html>
<script runat="server">
protected void Button1_Click(object sender, EventArgs e)
{
Label1.Text += "Your selected item is <br/>"+DropDownList1.SelectedItem.Text;
}
protected void Page_Load(object sender, EventArgs e)
{
}
</script>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:DropDownList ID="DropDownList1" runat="server" Height="30px" Width="149px" AutoPostBack="True">
<asp:ListItem Selected="True">select one</asp:ListItem>
<asp:ListItem>Apple </asp:ListItem>
<asp:ListItem>Mango</asp:ListItem>
<asp:ListItem>Orange</asp:ListItem>
</asp:DropDownList>
<br />
</div>
<asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" ControlToValidate="DropDownList1" ErrorMessage="RequiredFieldValidator" InitialValue="select one">Please Select Item</asp:RequiredFieldValidator>
<asp:Button ID="Button1" runat="server" OnClick="Button1_Click" Text="Button" />
<br />
<asp:Label ID="Label1" runat="server"></asp:Label>
</form>
</body>
</html>
II-Method
In the second method we use javascript to validate the Dropdownlist. First to add some Text and Value in the control, Now With the help of getElementById property we can access the value of this control. Generate error message with the help of alert dialog box when accessed value is match with selected value of this control.Complete code:
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default5.aspx.cs" Inherits="Default5" %><!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
<script>
function validate()
{
var req = document.getElementById('<%=DropDownList1.ClientID %>');
if(req.value=="0")
{
alert("please select one item");
}
}
</script>
</head>
<body>
<form id="form1" runat="server">
<asp:DropDownList ID="DropDownList1" runat="server">
<asp:ListItem Value="0" Text ="Select"></asp:ListItem>
<asp:ListItem Value="1" Text ="Education"></asp:ListItem>
<asp:ListItem Value="2" Text ="Technology"></asp:ListItem>
<asp:ListItem Value="3" Text ="Entertainment"></asp:ListItem>
</asp:DropDownList>
<p>
<asp:Button ID="Button1" runat="server" style="height: 26px" Text="Button" OnClientClick="validate()" />
</p>
</form>
</body>
</html>
Download : Complete Code
