在《使用篇》中我们谈到扩展的验证编程方式，并且演示了本解决方案的三大特性：消息提供机制的分离、多语言的支持和多验证规则的支持，我们现在来看看这样的验证解决方案最终是如何实现的。
目录：
一、为验证创建一个上下文：ValidatorContext
二、通过自定义ActionInvoker在进行操作执行之前初始化上下文
三、为Validator创建基类:ValidatorBaseAttribute
四、通过自定义ModelValidatorProvider在验证之前将不匹配Validator移除
五、RequiredValidatorAttribute的定义
“基于某个规则的验证”是本解决方案一个最大的卖点。为了保持以验证规则名称为核心的上下文信息，我定义了如下一个ValidatorContext（我们本打算将其命名为ValidationContext，无奈这个类型已经存在）。ValidatorContext的属性RuleName和Culture表示当前的验证规则和语言文化（默认值为当前线程的CurrentUICulture），而字典类型的属性Properties用户存放一些额外信息。当前ValidationContext的获取与设置通过静态Current完成。
1: public class ValidatorContext
2: {
3: [ThreadStatic]
4: private static ValidatorContext current;
5:
6: public string RuleName { get; private set; }
7: public CultureInfo Culture { get; private set; }
8: public IDictionary<string, object> Properties { get; private set; }
9:
10: public ValidatorContext(string ruleName, CultureInfo culture=null)
11: {
12: this.RuleName = ruleName;
13: this.Properties = new Dictionary<string, object>();
14: this.Culture = culture??CultureInfo.CurrentUICulture;
15: }
16:
17: public static ValidatorContext Current
18: {
19: get { return current; }
20: set { current = value; }
21: }
22: }
我们为ValidatorContext定义了如下一个匹配的ValidatorContextScope对象用于设置ValidatorContext的作用范围。
1: public class ValidatorContextScope : IDisposable
2: {
3: private ValidatorContext current = ValidatorContext.Current;
4: public ValidatorContextScope(string ruleName, CultureInfo culture = null)
5: {
6: ValidatorContext.Current = new ValidatorContext(ruleName, culture);
7: }
8: public void Dispose()
9: {
10: if (null == current)
11: {
12: foreach (object property in ValidatorContext.Current.Properties.Values)
13: {
14: IDisposable disposable = property as IDisposable;
15: if (null != disposable)
16: {
17: disposable.Dispose();
18: }
19: }
20: }
21: ValidatorContext.Current = current;
22: }
23: }
通过《使用篇》中我们知道当前的验证规则名称是通过ValidationRuleAttribute来设置的，该特性不仅仅可以应用在Action方法上，也可以应用在Controller类型上。当然Action方法上的ValidationRuleAttribute具有更高的优先级。如下面的代码片断所示，ValidationRuleAttribute就是一个包含Name属性的普通Attribute而已。
1: [AttributeUsage( AttributeTargets.Class| AttributeTargets.Method)]
2: public class ValidationRuleAttribute:Attribute
3: {
4: public string Name { get; private set; }
5: public ValidationRuleAttribute(string name)
6: {
7: this.Name = name;
8: }
9: }
很显然，以当前验证规则验证规则为核心的ValidatorContext需要在Action操作之前设置（严格地说应该在进行Model绑定之前），而在Action操作完成后清除。很自然地，我们可以通过自定义ActionInvoker来完成，为此我定义了如下一个直接继承自ControllerActionInvoker的ExtendedControllerActionInvoker类。
1: public class ExtendedControllerActionInvoker : ControllerActionInvoker
2: {
3: public ExtendedControllerActionInvoker()
4: {
5: this.CurrentCultureAccessor= (context=>
6: {
7: string culture = context.RouteData.GetRequiredString("culture");
8: if(string.IsNullOrEmpty(culture))
9: {
10: return null;
11: }
12: else
13: {
14: return new CultureInfo(culture);
15: }
16: });
17: }
18: public virtual Func<ControllerContext, CultureInfo> CurrentCultureAccessor { get; set; }
19: public override bool InvokeAction(ControllerContext controllerContext, string actionName)
20: {
21: CultureInfo originalCulture = CultureInfo.CurrentCulture;
22: CultureInfo originalUICulture = CultureInfo.CurrentUICulture;
23: try
24: {
25: CultureInfo culture = this.CurrentCultureAccessor(controllerContext);
26: if (null != culture)
27: {
28: Thread.CurrentThread.CurrentCulture = culture;
29: Thread.CurrentThread.CurrentUICulture = culture;
30: }
31: var controllerDescriptor = this.GetControllerDescriptor(controllerContext);
32: var actionDescriptor = this.FindAction(controllerContext, controllerDescriptor, actionName);
33: ValidationRuleAttribute attribute = actionDescriptor.GetCustomAttributes(true).OfType<ValidationRuleAttribute>().FirstOrDefault() as ValidationRuleAttribute;
34: if (null == attribute)
35: {
36: attribute = controllerDescriptor.GetCustomAttributes(true).OfType<ValidationRuleAttribute>().FirstOrDefault() as ValidationRuleAttribute;
37: }
38: string ruleName = (null == attribute) ? string.Empty : attribute.Name;
39: using (ValidatorContextScope contextScope = new ValidatorContextScope(ruleName))
40: {
41: return base.InvokeAction(controllerContext, actionName);
42: }
43: }
44: catch
45: {
46: throw;
47: }
48: finally
49: {
50: Thread.CurrentThread.CurrentCulture = originalCulture;
51: Thread.CurrentThread.CurrentUICulture = originalUICulture;
52: }
53: }
54: }
如上面的代码片断所示，在重写的InvokeAction方法中我们通过ControllerDescriptor/ActionDescriptor得到应用在Controller类型/Action方法上的ValidationRuleAttribute特性，并或者到设置的验证规则名称。然后我们创建ValidatorContextScope对象，而针对基类InvokeAction方法的执行就在该ValidatorContextScope中执行的。初次之外，我们还对当前线程的Culture进行了相应地设置，默认的Culture 信息来源于当前RouteData。
为了更方便地使用ExtendedControllerActionInvoker，我们定义了一个抽象的Controller基类：BaseController。BaseController是Controller的子类，在构造函数中我们将ActionInvoker属性设置成我们自定义的ExtendedControllerActionInvoker对象。
1: public abstract class BaseController: Controller
2: {
3: public BaseController()
4: {
5: this.ActionInvoker = new ExtendedControllerActionInvoker();
6: }
7: }
接下来我们才来看看真正用于验证的验证特性如何定义。我们的验证特性都直接或者间接地继承自具有如下定义的ValidatorBaseAttribute，而它使ValidationAttribute的子类。如下面的代码片断所示，ValidatorBaseAttribute还实现了IClientValidatable接口，以提供对客户端验证的支持。属性RuleName、MessageCategory、MessageId和Culture分别代表验证规则名称、错误消息的类别和ID号（通过这两个属性通过MessageManager这个独立的组件获取完整的错误消息）和基于的语言文化。
1: [AttributeUsage(AttributeTargets.Class|AttributeTargets.Field | AttributeTargets.Property, AllowMultiple = false)]
2: public abstract class ValidatorBaseAttribute : ValidationAttribute, IClientValidatable
3: {
4:
5: public string RuleName { get; set; }
6: public string MessageCategory { get; private set; }
7: public string MessageId { get; private set; }
8: public string Culture { get; set; }
9:
10: public ValidatorBaseAttribute(MessageManager messageManager, string messageCategory, string messageId, params object[] args)
11: : base(() => messageManager.FormatMessage(messageCategory, messageId, args))
12: {
13: this.MessageCategory = messageCategory;
14: this.MessageId = messageId;
15: }
16:
17: public ValidatorBaseAttribute(string messageCategory, string messageId, params object[] args)
18: : this(MessageManagerFactory.GetMessageManager(), messageCategory, messageId, args)
19: { }
20:
21: public virtual bool Match(ValidatorContext context, IEnumerable<ValidatorBaseAttribute> validators)
22: {
23: if (!string.IsNullOrEmpty(this.RuleName))
24: {
25: if (this.RuleName != context.RuleName)
26: {
27: return false;
28: }
29: }
30:
31: if (!string.IsNullOrEmpty(this.Culture))
32: {
33: if (string.Compare(this.Culture, context.Culture.Name, true) != 0)
34: {
35: return false;
36: }
37: }
38:
39: if (string.IsNullOrEmpty(this.Culture))
40: {
41: if (validators.Any(validator => validator.GetType() == this.GetType() && string.Compare(validator.Culture, context.Culture.Name, true) == 0))
42: {
43: return false;
44: }
45: }
46: return true;
47: }
48: public abstract IEnumerable<ModelClientValidationRule> GetClientValidationRules(ModelMetadata metadata, ControllerContext context);
49: private object typeId;
50: public override object TypeId
51: {
52: get { return (null == typeId) ? (typeId = new object()) : typeId; }
53: }
54: }
由于我们需要将多个相同类型的Validator特性应用到某个类型或者字段/属性上，我们需要通过AttributeUsageAttribute将AllowMultiple属性设置为True，此外需要重写TypeId属性。至于为什么需需要这么做，可以参考我的上一篇文章《在ASP.NET MVC中如何应用多个相同类型的ValidationAttribute？》。对于应用在同一个目标元素的多个相同类型的Validator特性，只有与当前ValidatorContext相匹配的才能执行，我们通过Match方法来进行匹配性的判断，具体的逻辑是这样的：
应用在Model类型或其属性/字段上的ValidationAttribute最终通过对应的ModelValidatorProvider（DataAnnotationsModelValidatorProvider）用于创建ModelValidator（DataAnnotationsModelValidator）。我们必须在ModelValidator创建之前将不匹配的Validator特性移除，才能确保只有与当前ValidatorContext相匹配的Validator特性参与验证。为此我们通过继承DataAnnotationsModelValidator自定义了如下一个ExtendedDataAnnotationsModelValidator。
1: public class ExtendedDataAnnotationsModelValidatorProvider : DataAnnotationsModelValidatorProvider
2: {
3: protected override IEnumerable<ModelValidator> GetValidators(ModelMetadata metadata, ControllerContext context, IEnumerable<Attribute> attributes)
4: {
5: var validators = attributes.OfType<ValidatorBaseAttribute>();
6: var allAttributes = attributes.Except(validators).ToList();
7: foreach (ValidatorBaseAttribute validator in validators)
8: {
9: if (validator.Match(ValidatorContext.Current, validators))
10: {
11: allAttributes.Add(validator);
12: }
13: }
14: return base.GetValidators(metadata, context, allAttributes);
15: }
16: }
如上面的代码片断所示，在重写的GetClientValidationRules方法中，输入参数attributes表示所有的ValidationAttribute，在这里我们根据调用ValidatorBaseAttribute的Match方法将不匹配的Validator特性移除，然后根据余下的ValidationAttribute列表调用基类GetValidators方法创建ModelValidator列表。值得一提的是，关于System.Attribute的Equals/GetHashCode方法的问题就从这个方法中发现的（详情参见《为什么System.Attribute的GetHashCode方法需要如此设计？》）。自定义ExtendedDataAnnotationsModelValidator在Global.asax的Application_Start方法中通过如下的方式进行注册。
1: protected void Application_Start()
2: {
3: //...
4: var provider = ModelValidatorProviders.Providers.OfType<DataAnnotationsModelValidatorProvider>().FirstOrDefault();
5: if (null != provider)
6: {
7: ModelValidatorProviders.Providers.Remove(provider);
8: }
9: ModelValidatorProviders.Providers.Add(new ExtendedDataAnnotationsModelValidatorProvider());
10: }
最后我们来看看用于验证必需字段的RequiredValidatorAttribute如何定义。IsValid用于服务端验证，而GetClientValidationRules生成调用客户端验证规则。
1: [AttributeUsage(AttributeTargets.Field | AttributeTargets.Property, AllowMultiple = true)]
2: public class RequiredValidatorAttribute : ValidatorBaseAttribute
3: {
4: public RequiredValidatorAttribute(string messageCategory, string messageId, params object[] args)
5: : base(messageCategory, messageId, args)
6: { }
7:
8: public override bool IsValid(object value)
9: {
10: if (value == null)
11: {
12: return false;
13: }
14: string str = value as string;
15: if (str != null)
16: {
17: return (str.Trim().Length != 0);
18: }
19: return true;
20: }
21:
22: public override IEnumerable<ModelClientValidationRule> GetClientValidationRules(ModelMetadata metadata, ControllerContext context)
23: {
24: return new ModelClientValidationRequiredRule[] { new ModelClientValidationRequiredRule(this.ErrorMessageString) };
25: }
26: }
通过扩展改善ASP.NET MVC的验证机制[实现篇],布布扣,bubuko.com
原文：http://www.cnblogs.com/lonelyxmas/p/3813416.html