MVC Model Binder

这篇博客是借助一个自己写的工程来理解model binder的过程.

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MVC通过路由系统，根据url找到对应的Action，然后再执行action，在执行action的时候，根据action的参数和数据来源比对，生成各个参数的值，这就是model binder.

IActionInvoker

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MVC中这个核心处理逻辑都在ControllerActionInvoker里，用reflector看，能看能到这个类继承了IActionInvoker接口

     public interface IActionInvoker
     {
         bool InvokeAction(ControllerContext controllerContext, string actionName);
     }

所以咱们可以根据代码模拟写出自己的CustomActionInvoker

以下是我自己写的ActionInvoker类

     public class CustomActionInvoker : IActionInvoker
     {

         public bool InvokeAction(ControllerContext controllerContext, string actionName)
         {
             bool flag = false;
             try
             {
                 //get controller type
                 Type controllerType = controllerContext.Controller.GetType();
                 //get controller descriptor
                 ControllerDescriptor controllerDescriptor = 
new ReflectedControllerDescriptor(controllerType);
                 //get action descriptor
                 ActionDescriptor actionDescriptor = 
controllerDescriptor.FindAction(controllerContext, actionName);
                 Dictionary<string, object> parameters = 

new Dictionary<string, object>(StringComparer.OrdinalIgnoreCase);
                 //get parameter-value entity
                 foreach (ParameterDescriptor parameterDescriptor in actionDescriptor.GetParameters())
                 {
                     Type parameterType = parameterDescriptor.ParameterType;
                     //get model binder
                     IModelBinder modelBinder = new CustomModelBinder();
                     IValueProvider valueProvider = controllerContext.Controller.ValueProvider;
                     string str = parameterDescriptor.BindingInfo.Prefix ?? parameterDescriptor.ParameterName;
                     ModelBindingContext bindingContext = new ModelBindingContext();
                     bindingContext.FallbackToEmptyPrefix = parameterDescriptor.BindingInfo.Prefix == null;
                     bindingContext.ModelMetadata = ModelMetadataProviders.Current.GetMetadataForType(null, parameterType);
                     bindingContext.ModelName = str;
                     bindingContext.ModelState = controllerContext.Controller.ViewData.ModelState;
                     bindingContext.ValueProvider = valueProvider;
                     parameters.Add(parameterDescriptor.ParameterName, 
modelBinder.BindModel(controllerContext, bindingContext));
                 }
                 ActionResult result = (ActionResult)actionDescriptor.Execute(controllerContext, parameters);
                 result.ExecuteResult(controllerContext);
                 flag = true;
             }
             catch (Exception ex)
             {
                 //log
             }
             return flag;
         }
     }

以下详细解释下执行过程

*Descriptor

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执行过程中涉及到三个Descriptor,ControllerDescriptor,ActionDescriptor,ParameterDescriptor

ControllerDescriptor主要作用是根据action name获取到ActionDescriptor,代码中使用的是MVC自带的ReflectedControllerDescriptor,从名字就可以看出来，主要是靠反射获取到action.

ActionDescriptor,主要作用是获取parameterDescriptor,然后execute action.

parameterDescriptor,描述的是action的参数信息，包括name、type等

ModelBinder

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最核心的方法. 将传递的数据和参数一一对应，笔者是自己写的CustomModelBinder,MVC默认用的是DefaultModelBinder 都实现了接口IModelBinder

     public interface IModelBinder
     {
         object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext);
     }

其中CustomModelBinder的代码如下

     public class CustomModelBinder : IModelBinder
     {

         public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
         {
             return this.GetModel(controllerContext, bindingContext.ModelType, bindingContext.ValueProvider, bindingContext.ModelName);
         }

         public object GetModel(ControllerContext controllerContext, Type modelType, IValueProvider valueProvider, string key)
         {
             if (!valueProvider.ContainsPrefix(key))
             {
                 return null;
             }
             return valueProvider.GetValue(key).ConvertTo(modelType);
         }
     }

注：我只是实现了简单的基本类型

中间有最核心的方法

valueProvider.GetValue(key).ConvertTo(modelType)

ValueProvider

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MVC默认提供了几种ValueProvider,每种都有对应的ValueProviderFactory,每种ValueProvider都对应着自己的数据源

     ValueProviderFactoryCollection factorys = new ValueProviderFactoryCollection();
     factorys.Add(new ChildActionValueProviderFactory());
     factorys.Add(new FormValueProviderFactory());
     factorys.Add(new JsonValueProviderFactory());
     factorys.Add(new RouteDataValueProviderFactory());
     factorys.Add(new QueryStringValueProviderFactory());
     factorys.Add(new HttpFileCollectionValueProviderFactory());

注册ActionInvoker

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上述过程讲完之后，还缺一个怎么应用上自己写的ActionInvoker,在Controller里提供了虚方法CreateActionInvoker

         protected override IActionInvoker CreateActionInvoker()
         {
             return new CustomActionInvoker();
         }

到此，整个过程已讲完。