RequiredFieldValidator to validate RadioButtonList in asp.net c#

RequiredFieldValidator to validate RadioButtonList
RequiredFieldValidator validation control make an asp.net web server input control as like a mandatory field. input control validation fails if the value of control does not change from it's initial value. so it will be a required field (input control) for submit web form. user must be input some value to pass the validation. you cannot pass a validation by only entered space. you can set the requiredfieldvalidator InitialValue property to select another item except initial value for passing validation. you can set the ErrorMessage property value to display error message when validation failed.

this example demonstrate you how can we validate radiobuttonlist control using requiredfieldvalidator. this validation control make radiobuttonlist a mandatory (required) field. so user must be select (checked) a list item from radiobuttonlist to pass the validation and submit form. it is very useful when radiobuttonlist have no default selection. if the validation fail, the requiredfieldvalidator show a predefined error message that tell you radiobuttonlist is a required field.
RadioButtonListValidation.aspx

<%@ Page Language="C#" %>

<!DOCTYPE html>

<script runat="server">
    protected void Button1_Click(object sender, EventArgs e)
    {
        Label1.Text = "Your favorite: ";
        Label1.Text += RadioButtonList1.SelectedItem.Text.ToString();
    }
</script>

<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
    <title>asp.net RequiredFieldValidator example: how to validate RadioButtonList</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <h2 style="color:Green">RadioButtonList Validation</h2>
        <asp:Label 
            ID="Label1"
            runat="server"
            Font-Size="Large"
            ForeColor="Crimson"
            >
        </asp:Label>
        <br /><br />
        <asp:Label 
            ID="Label2"
            runat="server"
            Text="Favorite"
            Font-Bold="true"
            ForeColor="DodgerBlue"
            >
        </asp:Label>
        <asp:RadioButtonList 
            ID="RadioButtonList1"
            runat="server"
            RepeatColumns="3"
            BackColor="DodgerBlue"
            ForeColor="AliceBlue"
            BorderColor="DarkBlue"
            BorderWidth="2"
            >
            <asp:ListItem>CheckBoxList</asp:ListItem>
            <asp:ListItem>TreeView</asp:ListItem>
            <asp:ListItem>Button</asp:ListItem>
            <asp:ListItem>SqlDataSource</asp:ListItem>
            <asp:ListItem>GridView</asp:ListItem>
            <asp:ListItem>Calendar</asp:ListItem>
            <asp:ListItem>BulletedList</asp:ListItem>
        </asp:RadioButtonList>
        <asp:RequiredFieldValidator 
            ID="ReqiredFieldValidator1"
            runat="server"
            ControlToValidate="RadioButtonList1"
            ErrorMessage="Select your favorite!"
            >
        </asp:RequiredFieldValidator>
        <br />
        <asp:Button 
            ID="Button1" 
            runat="server" 
            ForeColor="DodgerBlue" 
            Text="Submit Favorite"
            OnClick="Button1_Click"
            />
    </div>
    </form>
</body>
</html>
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