爱上MVC3~为下拉列表框添加一个自定义验证规则

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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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