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。