爱上MVC3~为下拉列表框添加一个自定义验证规则

开发它的原因：

之前的同事，也是我的哥们，问我下拉列表框是否可以支持验证，这个问题看似简单，但确实ＭＶＣ里有为我们提供，所以，只能自己写个扩展了，即自己写一个attribute特性，让它继承ValidationAttribute，使它可以与其它ＭＶＣ提供的验证一起使用．

ＭＶＣ验证是怎么运行的：

在ＭＶＣ的特性验证，很方便，很直接，它无论是在数据安全性上还是在页面表现上都做的不错，它的运行机制是这样的，前台表单验证规则有个名称，然后前台ＪＳ有对这个规则编写的代码，用来控制前台ＨＴＭＬ标记的显示，而后台主要是生成验证规则和向前台参数赋值的。事实上，我们要知道的是，ＭＶＣ验证不是简单的后台验证，它还有对前台页面的控制的ＪＳ部分，它一般被继承到了jquery.validate.min.js里了，如果我们要是自己开发一套验证规则，也需要自己的ＪＳ库与相配合。

说干就干

Ｃ#部分：

　  [AttributeUsage(AttributeTargets.Property | AttributeTargets.Field | AttributeTargets.Parameter, AllowMultiple = false)]

    public sealed class NotDefaultValueAttribute : ValidationAttribute, IClientValidatable

    {

        public string InputString { get; set; }

        public NotDefaultValueAttribute()

        {

            ErrorMessage = "请选其中一项";

        }

        public IEnumerable<ModelClientValidationRule> GetClientValidationRules(ModelMetadata metadata, ControllerContext context)

        {

            ModelClientValidationRule rule = new ModelClientValidationRule

           {

               ValidationType = "notdefaultvalue",

               ErrorMessage = FormatErrorMessage(metadata.GetDisplayName())

           };

            rule.ValidationParameters["inputstring"] = InputString;

            yield return rule;

        }

        public override bool IsValid(object value)

        {

            if (value == null)

                return true;

            string inputString = (string)value;

            if (inputString.Contains(InputString))

            {

                return false;

            }

            return true;

        }

    }

为viewmodel添加特性

  public class TestModel

    {

        [Required]

        [Display(Name = "用户名")]

        public string UserName { get; set; }

        [Required]

        [DataType(DataType.Password)]

        [Display(Name = "密码")]

        public string Password { get; set; }

        [Display(Name = "爱好")]

        [NotDefaultValue(InputString = "")]/*如果用户选择为１，则验证不通过*/

        public IEnumerable<SelectListItem> Liker { get; set; }

    }

在前面添加相对应的ＪＳ代码，建议将自定义的ＪＳ库放在一个单独的文件里，这样扩展性更强一些。

    $.validator.addMethod('notdefaultvalue', function (value, element, param) {

        if (value == false) {

            return true;

        }

        if (value.indexOf(param) != -) {

            return false;

        }

        else {

            return true;

        }

    });

    $.validator.unobtrusive.adapters.addSingleVal('notdefaultvalue', 'inputstring');

ＯＫ，现在就可以运行我们的程序了，看看效果吧

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QgDkUD4lA0IA5FA+JQNCAORQPiUDQgDkUD4lA0IA5FA+JQNCAORQPiUDQgjv8DvdLYNhuI/fcAAAAASUVORK5CYII=" 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怎么样，像这种扩展，我们还可以写很多，举一反三吧，呵呵！

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