Asp.net MVC中的提供非常简单易用的数据验证解决方案. 通过System.ComponentModel.DataAnnotations提供的很多的验证规则(Required, StringLength等)。但是常常有这样的需求，我们希望能够把model的验证规则，保存到数据或者xml文件中，而不是代码里, 这样的好处是，我们可以很方便的修改验证规则和错误消息，避免需要重新发布网站。
这篇文章，一起来看看是如何通过自定义ModelValidatorProvider来通过XML文件配置对于Model的验证。
阅读目录:
一、简单回顾内置MVC验证的使用
二、分析MVC验证的内部过程
三、一个例子，针对ContactInfo的验证
四、具体实现和应用XmlModelValidatorProvider
下面是典型的MVC验证规则的代码和页面展示效果。
1. 实际做验证的是ModelValidator
当我们如上图，在为Person类添加了各种验证规则的dataannotation attributes后，实际操刀来做验证的是DataAnnotationsModelValidator类.DataAnnotationsModelValidator继承自抽象类ModelValidator，实现了抽象方法Validate, 在该方法中根据Person类中定义的验证规则，对于所有Person的实例进行验证，同时返回一个ModelValidationResult的集合。
2. ModelValidator是由ModelValidatorProviders提供的
MVC在验证过程中使用到的ModelValidator又是由ModelValidatorProviders类提供的, ModelValidatorProviders是一个抽象类，有个抽象方法GetValidators.
该类的定义是这样的
namespace System.Web.Mvc
{
public abstract class ModelValidatorProvider
{
public abstract IEnumerable<ModelValidator> GetValidators(ModelMetadata metadata, ControllerContext context);
}
}
实际运行中，MVC使用的是继承于ModelValidatorProvider, 实现了GetValidators方法的DataAnnotationsModelValidatorProvider类.
3. MVC的验证过程中可以存在多个ModelValidatorProvider
MVC中可以多个ModelValidatorProvider同时起作用, 他们的效果可以叠加。我们可以使用默认的根据Attribute来定义验证规则的DataAnnotationsModelValidatorProvider，也还可以同时使用我们下面的XmlModelValidatorProvider从xml文件中获取验证规则来做验证。
下面这个ContactInfo类是我们用来做实际验证的，包含了一些常用的典型的验证，Required, Email, Url等
public class ContactInfo
{
public string FirstName { get; set; }
public string LastName{get;set;}
public string Email{get;set;}
public string Url{get;set;}
}
下面的这个xml文件，定义的是关于ContactInfo类的验证规则，以前我们是写在ContactInfo类中的，现在把它分离出来，放到Content\Validation\Rules\ContactInfo.xml文件中.
这里的message中的值只是一个message的key， message的具体内容放在另外一个xml文件中。
<?xml version="1.0" encoding="utf-8" ?> <model> <validator property="FirstName" type="Required" message="FirstName_Required" /> <validator property="FirstName" type="StringLength" arg-int="50" message="FirstName_Length" /> <validator property="LastName" type="Required" message="LastName_Required" /> <validator property="LastName" type="StringLength" arg-int="255" message="LastName_Length" /> <validator property="Email" type="Required" message="Email_Required" /> <validator property="Email" type="StringLength" arg-int="255" message="Email_Length" /> <validator property="Email" type="RegularExpression" arg="^[\w-]+(\.[\w-]+)*@[\w-]+(\.[\w-]+)+$" message="Email_RegularExpression" /> <validator property="Url" type="StringLength" arg-int="255" message="Url_Length" /> <validator property="Url" type="RegularExpression" arg="(http://)?(www\.)?\w+\.(com|net|edu|org)" message="Url_RegularExpression" /> </model>
存放message的是Content\Validation\Messages\ContactInfo.xml文件
<?xml version="1.0" encoding="utf-8" ?> <messages> <!-- filed error message --> <message key="FirstName_Required" text="The Frist Name field is required."></message> <message key="FirstName_Length" text="The field maximum length is 50"></message> <message key="LastName_Required" text="The Last Name field is required."></message> <message key="LastName_Length" text="The field maximum length is 255"></message> <message key="Email_Required" text="The Email field is required."></message> <message key="Email_Length" text="The field maximum length is 255"></message> <message key="Email_RegularExpression" text="Invalid email."></message> <message key="Url_Length" text="The field maximum length is 255"></message> <message key="Url_RegularExpression" text="Invalid URL."></message> </messages>
下面是我们最重要的XmlModelValidatorProvider的实现代码
public class XmlModelValidatorProvider : ModelValidatorProvider
{
// 用来保存System.ComponentModel.DataAnnotations中已经存在的验证规则，也就是MVC自带的Required等验证规则， 因为我们只是验证规则的"源"不一样，一个是代码中，一个是xml，但是验证过程是一样的，所以要重用MVC中的已经写好的验证。
private readonly Dictionary<string, Type> _validatorTypes;
private readonly string _xmlFolderPath = HttpContext.Current.Server.MapPath("~//Content//Validation//Rules");
public XmlModelValidatorProvider()
{
_validatorTypes = Assembly.Load("System.ComponentModel.DataAnnotations").GetTypes()
.Where(t => t.IsSubclassOf(typeof (ValidationAttribute)))
.ToDictionary(t => t.Name, t => t);
}
#region Stolen from DataAnnotationsModelValidatorProvider
// delegate that converts ValidationAttribute into DataAnnotationsModelValidator
internal static DataAnnotationsModelValidationFactory DefaultAttributeFactory =
(metadata, context, attribute) => new DataAnnotationsModelValidator(metadata, context, attribute);
internal static Dictionary<Type, DataAnnotationsModelValidationFactory> AttributeFactories = new Dictionary
<Type, DataAnnotationsModelValidationFactory>
{
{
typeof (RangeAttribute),
( metadata, context, attribute)
=>
new RangeAttributeAdapter (metadata, context, ( RangeAttribute ) attribute)
},
{
typeof (RegularExpressionAttribute),
( metadata, context, attribute)
=>
new RegularExpressionAttributeAdapter (metadata, context, ( RegularExpressionAttribute ) attribute)
},
{
typeof (RequiredAttribute),
( metadata, context, attribute) =>
new RequiredAttributeAdapter (metadata, context, ( RequiredAttribute ) attribute)
},
{
typeof (StringLengthAttribute),
( metadata, context, attribute) =>
new StringLengthAttributeAdapter (metadata, context, ( StringLengthAttribute ) attribute)
}
};
#endregion
// 重写GetValidators方法，该从xml文件中获取。根据xml的配置，返回对应的Validator集合
public override IEnumerable<ModelValidator> GetValidators(ModelMetadata metadata, ControllerContext context)
{
var results = new List<ModelValidator>();
// whether the validation is for a property or model
// (remember we can apply validation attributes to a property or model and same applies here as well)
var isPropertyValidation = metadata.ContainerType != null && !String.IsNullOrEmpty(metadata.PropertyName);
var rulesPath = String.Format("{0}\\{1}.xml", _xmlFolderPath,
isPropertyValidation ? metadata.ContainerType.Name : metadata.ModelType.Name);
var rules = File.Exists(rulesPath)
? XElement.Load(rulesPath).XPathSelectElements(String.Format(
"./validator[@property=‘{0}‘]",
isPropertyValidation ? metadata.PropertyName : metadata.ModelType.Name)).ToList()
: new List<XElement>();
// Produce a validator for each validation attribute we find
foreach (var rule in rules)
{
DataAnnotationsModelValidationFactory factory;
var validatorType = _validatorTypes[String.Concat(rule.Attribute("type").Value, "Attribute")];
if (!AttributeFactories.TryGetValue(validatorType, out factory))
{
factory = DefaultAttributeFactory;
}
var validator = (ValidationAttribute) Activator.CreateInstance(validatorType, GetValidationArgs(rule));
validator.ErrorMessage = rule.Attribute("message") != null &&
!String.IsNullOrEmpty(rule.Attribute("message").Value)
? GetValidationMessage(isPropertyValidation ? metadata.ContainerType.Name : metadata.ModelType.Name, rule.Attribute("message").Value)
: null;
results.Add(factory(metadata, context, validator));
}
return results;
}
private string GetValidationMessage(string model, string key)
{
return MessageProvider.GetViewModelValidationMessage(model, key);
}
// read the arguments passed to the validation attribute and cast it their respective type.
private object[] GetValidationArgs(XElement rule)
{
var validatorArgs = rule.Attributes().Where(a => a.Name.ToString().StartsWith("arg"));
var args = new object[validatorArgs.Count()];
var i = 0;
foreach (var arg in validatorArgs)
{
var argName = arg.Name.ToString();
var argValue = arg.Value;
if (!argName.Contains("-"))
{
args[i] = argValue;
}
else
{
var argType = argName.Split(‘-‘)[1];
switch (argType)
{
case "int":
args[i] = int.Parse(argValue);
break;
case "datetime":
args[i] = DateTime.Parse(argValue);
break;
case "char":
args[i] = Char.Parse(argValue);
break;
case "double":
args[i] = Double.Parse(argValue);
break;
case "decimal":
args[i] = Decimal.Parse(argValue);
break;
case "bool":
args[i] = Boolean.Parse(argValue);
break;
default:
args[i] = argValue;
break;
}
}
}
return args;
}
}
最后，在Global.cs文件中，把XmlModelValidatorProvider添加到MVC的ModelValidatorProvidersCollection中
ModelValidatorProviders.Providers.Add(new XmlModelValidatorProvider());
MVC数据验证原理及自定义ModelValidatorProvider实现无编译修改验证规则和错误信息
原文：http://www.cnblogs.com/webenh/p/7691766.html