In this article I will explain with an example, how to perform validation for CheckBox in ASP.Net Core Razor Pages.
The validations will be performed using Model class, Custom Data Annotation attribute and jQuery.
Custom Validation Data Annotations Attribute for CheckBox
The Required Data Annotation attribute does not work for Boolean validation i.e. performing validation Checked or Unchecked for a CheckBox.
Hence, a new class will be created for developing Custom Validation Data Annotations Attribute for CheckBox. This attribute will validate the CheckBox as Boolean validation i.e. only two values True or False and will raise error when the value is False.
using System.ComponentModel.DataAnnotations;
using Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
namespace CheckBox_Validation_Razor_Core
{
public class CheckBoxRequired: ValidationAttribute, IClientModelValidator
{
public override bool IsValid(object value)
{
if (value is bool)
{
return (bool)value;
}
return false;
}
public void AddValidation(ClientModelValidationContext context)
{
context.Attributes.Add("data-val-checkboxrequired", FormatErrorMessage(context.ModelMetadata.GetDisplayName()));
}
}
}
Model
The following Model class consists of one property TermsConditions to which the CheckBoxRequired Custom Data Annotation attribute has been applied.
The CheckBoxRequired Custom Data Annotation has been specified with a property Error Message with a string value. As the name suggests, this string value will be displayed to the user when the validation fails.
public class PersonModel
{
[Display(Name = "I accept the above terms and conditions.")]
[CheckBoxRequired(ErrorMessage = "Please accept the terms and condition.")]
public bool TermsConditions { get; set; }
}
Razor PageModel (Code-Behind)
The PageModel consists of following two Handler methods.
Handler method for handling GET operation
This Handler method handles the GET calls, for this particular example it is not required and hence left empty.
Handler method for handling POST operation
This Handler method handles the POST operation and when the form is submitted, the object of the PersonModel class is sent to this method.
public class IndexModel : PageModel
{
public PersonModel Person { get; set; }
public void OnGet()
{
}
public void OnPostSubmit(PersonModel person)
{
}
}
Razor Page (HTML)
The Form
The HTML of Razor Page consists of an HTML Form which has been created using following ASP.Net Tag Helpers attribute.
method – It specifies the Form Method i.e. GET or POST. In this case it will be set to POST.
The Form consists of a HTML Input CheckBox, a Label, a SPAN element and a Submit Button.
The Input CheckBox has been assigned with asp-for Tag Helper attribute and its value is set with the TermsConditions property of the PersonModel object. Thus, this signifies that the validation will be performed for the TermsConditions property.
The Label has been assigned with asp-for Tag Helper attribute and here also its value is set with the TermsConditions property of the PersonModel object which signifies that it is used for displaying the Model property name.
The SPAN has been assigned with asp-validation-for Tag Helper attribute and here also its value is set with the TermsConditions property of the PersonModel object which signifies that it is used for displaying the Validation message for the TermsConditions property.
The Submit Button has been set with the POST Handler method using the asp-page-handler attribute.
Note: In the Razor PageModel, the Handler method name is OnPostSubmit but here it will be specified as Submit when calling from the Razor HTML Page.
When the Submit button is clicked, the Form gets submitted and the TermsConditions value is sent to the POST Handler method.
Enabling Client-Side validations
By default, the validations performed using Data Annotations and Model class is performed on Server Side.
In order to enable Client-Side validations, you will need to inherit the following script files.
1. jquery.js
2. jquery.validate.js
3. jquery.validate.unobtrusive.js
Once, the above files are inherited automatically the Client-Side validations using Data Annotations is enabled.
Finally, in order to make the CheckBoxRequired Custom Data Annotation validation to work on Client Side, the validation rule needs to be added to the jQuery Unobtrusive Validation Adapters.
@page
@addTagHelper*, Microsoft.AspNetCore.Mvc.TagHelpers
@model CheckBox_Validation_Razor_Core.Pages.IndexModel
@{
Layout = null;
}
<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width" />
<title>Index</title>
<style type="text/css">
body { font-family: Arial; font-size: 10pt; }
.error { color: red; }
</style>
</head>
<body>
<form method="post">
<table>
<tr>
<td><input asp-for="Person.TermsConditions" type="checkbox" /></td>
<td><label asp-for="Person.TermsConditions"></label></td>
</tr>
<tr>
<td></td>
<td><span asp-validation-for="Person.TermsConditions" class="error"></span></td>
</tr>
<tr>
<td></td>
<td><input type="submit" value="Submit" asp-page-handler="Submit" /></td>
</tr>
</table>
</form>
<!--OPTIONAL: Add the following scripts for enabling Client Side validation.-->
<script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.6.0/jquery.js"></script>
<script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/jquery-validate/1.19.3/jquery.validate.js"></script>
<script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/jquery-validation-unobtrusive/3.2.12/jquery.validate.unobtrusive.js"></script>
<script type="text/javascript">
(function ($) {
$.validator.unobtrusive.adapters.addBool("checkboxrequired", "required");
}(jQuery));
</script>
</body>
</html>
Screenshot
![CheckBox validation in ASP.Net Core Razor Pages]()
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