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 IActionInvoker
2     {
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 type
10                 Type controllerType = controllerContext.Controller.GetType();
11                 //get controller descriptor
12                 ControllerDescriptor controllerDescriptor = 
new ReflectedControllerDescriptor(controllerType);
13                 //get action descriptor
14                 ActionDescriptor actionDescriptor = 
controllerDescriptor.FindAction(controllerContext, actionName);
15                 Dictionary<string, object> parameters = 

new Dictionary<string, object>(StringComparer.OrdinalIgnoreCase);
16                 //get parameter-value entity
17                 foreach (ParameterDescriptor parameterDescriptor in actionDescriptor.GetParameters())
18                 {
19                     Type parameterType = parameterDescriptor.ParameterType;
20                     //get model binder
21                     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                 //log
39             }
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 IModelBinder
2     {
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。