Giorgos Manoltzas Giorgos Manoltzas - 11 months ago 55
C# Question

client-side validation in custom validation attribute - mvc 4

I have followed some articles and tutorials over the internet in order to create a custom validation attribute that also supports client-side validation in an mvc 4 website. This is what i have until now:


[AttributeUsage(AttributeTargets.Property, AllowMultiple = true)] //Added
public class RequiredIfAttribute : ValidationAttribute, IClientValidatable
private readonly string condition;
private string propertyName; //Added

public RequiredIfAttribute(string condition)
this.condition = condition;
this.propertyName = propertyName; //Added

protected override ValidationResult IsValid(object value, ValidationContext validationContext)
PropertyInfo propertyInfo = validationContext.ObjectType.GetProperty(this.propertyName); //Added
Delegate conditionFunction = CreateExpression(validationContext.ObjectType, _condition);
bool conditionMet = (bool)conditionFunction.DynamicInvoke(validationContext.ObjectInstance);

if (conditionMet)
if (value == null)
return new ValidationResult(FormatErrorMessage(null));

return ValidationResult.Success;

private Delegate CreateExpression(Type objectType, string expression)
LambdaExpression lambdaExpression = System.Linq.Dynamic.DynamicExpression.ParseLambda(objectType, typeof(bool), expression); //Added
Delegate function = lambdaExpression.Compile();
return function;

public IEnumerable<ModelClientValidationRule> GetClientValidationRules(ModelMetadata metadata, ControllerContext context)
var modelClientValidationRule = new ModelClientValidationRule
ValidationType = "requiredif",
ErrorMessage = ErrorMessage //Added

modelClientValidationRule.ValidationParameters.Add("param", this.propertyName); //Added
return new List<ModelClientValidationRule> { modelClientValidationRule };

Then i applied this attribute in a property of a class like this

[RequiredIf("InAppPurchase == true", "InAppPurchase", ErrorMessage = "Please enter an in app purchase promotional price")] //Added "InAppPurchase"
public string InAppPurchasePromotionalPrice { get; set; }

public bool InAppPurchase { get; set; }

So what i want to do is display an error message that field InAppPurchasePromotionalPrice is required when InAppPurchase field is true (that means checked in the form). The following is the relevant code form the view:

<div class="control-group">
<label class="control-label" for="InAppPurchase">Does your app include In App Purchase?</label>
<div class="controls">
@Html.CheckBoxFor(o => o.InAppPurchase)
@Html.LabelFor(o => o.InAppPurchase, "Yes")
<div class="control-group" id="InAppPurchasePromotionalPriceDiv" @(Model.InAppPurchase == true ? Html.Raw("style='display: block;'") : Html.Raw("style='display: none;'"))>
<label class="control-label" for="InAppPurchasePromotionalPrice">App Friday Promotional Price for In App Purchase: </label>
<div class="controls">
@Html.TextBoxFor(o => o.InAppPurchasePromotionalPrice, new { title = "This should be at the lowest price tier of free or $.99, just for your App Friday date." })
<span class="help-inline">
@Html.ValidationMessageFor(o => o.InAppPurchasePromotionalPrice)

This code works perfectly but when i submit the form a full post is requested on the server in order to display the message. So i created JavaScript code to enable client-side validation:


(function ($) {
$.validator.addMethod('requiredif', function (value, element, params) {
/*var inAppPurchase = $('#InAppPurchase').is(':checked');

if (inAppPurchase) {
return true;

return false;*/

var isChecked = $(param).is(':checked');

if (isChecked) {
return false;

return true;
}, '');

$.validator.unobtrusive.adapters.add('requiredif', ['param'], function (options) {
options.rules["requiredif"] = '#' + options.params.param;
options.messages['requiredif'] = options.message;

This is the proposed way in msdn and tutorials i have found

Of course i have also inserted the needed scripts in the form:

  1. jquery.unobtrusive-ajax.min.js

  2. jquery.validate.min.js

  3. jquery.validate.unobtrusive.min.js

  4. requiredif.js

BUT...client side validation still does not work. So could you please help me find what am i missing? Thanks in advance.

Answer Source

Take a look at this:

Using this tutorial I got my custom validation code running with no problem. The only difference I can spot in your code is the way you created the $.validator.unobtrusive.adapters.add function. The parameters are a little bit different but, maybe, the problem is just that you have not defined the rule part of your adapter.

Try using something like this:

$.validator.unobtrusive.adapters.add("requiredif", ["requiredif"], function (options) {
    options.rules["requiredif"] = "#" + options.params.requiredif;
    options.messages["requiredif"] = options.message;

or this

$.validator.unobtrusive.adapters.add("requiredif", function (options) {
    options.rules["requiredif"] = "#" +'.', '_'); // mvc html helpers
    options.messages["requiredif"] = options.message;

About the rule (taken from the link):

The jQuery rules array for this HTML element. The adapter is expected to add item(s) to this rules array for the specific jQuery Validate validators that it wants to attach. The name is the name of the jQuery Validate rule, and the value is the parameter values for the jQuery Validate rule.