ASPNet CheckBox Required Validation using Custom Validator and JavaScript

In this article I will explain with an example, how to validate CheckBox control using CustomValidator and JavaScript in ASP.Net.

The HTML Markup consists of following controls:

CheckBox – For capturing user input.

Button – For submitting the Form.

CustomValidator – To ensure the CheckBox is checked before PostBack.

The CustomValidator has been set with the following event handler:

ClientValidationFunction – For setting the ValidateCheckBox JavaScript function.

<asp:CheckBox ID="CheckBox1" runat="server" />

<asp:CustomValidator ID="CustomValidator1" runat="server" ErrorMessage="Required" ClientValidationFunction="ValidateCheckBox"></asp:CustomValidator>

<asp:Button ID="btnSubmit" runat="server" Text="Submit" />

When the Submit Button is clicked, the ValidateCheckBox JavaScript function gets called.

Inside the ValidateCheckBox JavaScript function, a check is performed whether the CheckBox is checked or not.

If checked then it returns TRUE else FALSE.

function ValidateCheckBox(sender, args) {

args.IsValid = document.getElementById("<%=CheckBox1.ClientID%>").checked ? : false;

}

</script>

The above code has been tested in the following browsers.
Microsoft Edge

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ASP.Net CheckBox Required Validation using Custom Validator and JavaScript