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

1     public interface IActionInvoker2     {3         bool InvokeAction(ControllerContext controllerContext, string actionName);4     }

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

 1     public class CustomActionInvoker : IActionInvoker 2     { 3  4         public bool InvokeAction(ControllerContext controllerContext, string actionName) 5         { 6             bool flag = false; 7             try 8             { 9                 //get controller type10                 Type controllerType = controllerContext.Controller.GetType();11                 //get controller descriptor12                 ControllerDescriptor controllerDescriptor = 
new ReflectedControllerDescriptor(controllerType);13                 //get action descriptor14                 ActionDescriptor actionDescriptor = 
controllerDescriptor.FindAction(controllerContext, actionName);15                 Dictionary<string, object> parameters = 

new Dictionary<string, object>(StringComparer.OrdinalIgnoreCase);16                 //get parameter-value entity17                 foreach (ParameterDescriptor parameterDescriptor in actionDescriptor.GetParameters())18                 {19                     Type parameterType = parameterDescriptor.ParameterType;20                     //get model binder21                     IModelBinder modelBinder = new CustomModelBinder();22                     IValueProvider valueProvider = controllerContext.Controller.ValueProvider;23                     string str = parameterDescriptor.BindingInfo.Prefix ?? parameterDescriptor.ParameterName;24                     ModelBindingContext bindingContext = new ModelBindingContext();25                     bindingContext.FallbackToEmptyPrefix = parameterDescriptor.BindingInfo.Prefix == null;26                     bindingContext.ModelMetadata = ModelMetadataProviders.Current.GetMetadataForType(null, parameterType);27                     bindingContext.ModelName = str;28                     bindingContext.ModelState = controllerContext.Controller.ViewData.ModelState;29                     bindingContext.ValueProvider = valueProvider;30                     parameters.Add(parameterDescriptor.ParameterName, 
modelBinder.BindModel(controllerContext, bindingContext));31                 }32                 ActionResult result = (ActionResult)actionDescriptor.Execute(controllerContext, parameters);33                 result.ExecuteResult(controllerContext);34                 flag = true;35             }36             catch (Exception ex)37             {38                 //log39             }40             return flag;41         }42     }

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

1     public interface IModelBinder2     {3         object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext);4     }

其中CustomModelBinder的代码如下

 1     public class CustomModelBinder : IModelBinder 2     { 3  4         public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext) 5         { 6             return this.GetModel(controllerContext, bindingContext.ModelType, bindingContext.ValueProvider, bindingContext.ModelName); 7         } 8  9         public object GetModel(ControllerContext controllerContext, Type modelType, IValueProvider valueProvider, string key)10         {11             if (!valueProvider.ContainsPrefix(key))12             {13                 return null;14             }15             return valueProvider.GetValue(key).ConvertTo(modelType);16         }17     }

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

1     ValueProviderFactoryCollection factorys = new ValueProviderFactoryCollection();2     factorys.Add(new ChildActionValueProviderFactory());3     factorys.Add(new FormValueProviderFactory());4     factorys.Add(new JsonValueProviderFactory());5     factorys.Add(new RouteDataValueProviderFactory());6     factorys.Add(new QueryStringValueProviderFactory());7     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

1         protected override IActionInvoker CreateActionInvoker()2         {3             return new CustomActionInvoker();4         }

到此，整个过程已讲完。