MVC中Action参数绑定的过程

一、题外话

上一篇：MVC中Action的执行过程

ControllerContext

封装有了与指定的 RouteBase 和 ControllerBase 实例匹配的 HTTP 请求的信息。

二、Model绑定者

2.1相关说明

http请求中的参数绑定到Model，是由实现了IModelBinder的类来完成的。我们称这样的类叫做Model绑定者

using System;
namespace System.Web.Mvc
{/// <summary>Defines the methods that are required for a model binder.</summary>public interface IModelBinder{/// <summary>Binds the model to a value by using the specified controller context and binding context.</summary>/// <returns>The bound value.</returns>/// <param name="controllerContext">The controller context.</param>/// <param name="bindingContext">The binding context.</param>object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext);}
}

2.2Model绑定者实现绑定的途径

1）直接在参数上绑定

using System;
using System.Web;
using System.Web.Mvc;namespace MVC_ST_2.Controllers
{public class Person{public string Name { get; set; }public int Age { get; set; }}public class PersonModelBinder : IModelBinder{public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext){HttpRequestBase request = controllerContext.HttpContext.Request;var p = new Person();p.Name = request["Name"];p.Age =int.Parse( request["Age"]);return p;}}public class HomeController : Controller{//通过参数标记public ActionResult Index([ModelBinder(typeof(PersonModelBinder))] Person p){return View();}public ActionResult Index2(Person p){return View();}}
}

2）在model上加标记

    [ModelBinder(typeof(PersonModelBinder))] public class Person{public string Name { get; set; }public int Age { get; set; }}

3）ModelBinders.Binders中注册

protected void Application_Start(){ModelBinders.Binders[typeof(Person)] = new PersonModelBinder();
}

2.3 Action中是如何调用绑定者的？

以下是

private IModelBinder GetModelBinder(ParameterDescriptor parameterDescriptor)
{return parameterDescriptor.BindingInfo.Binder ?? this.Binders.GetBinder(parameterDescriptor.ParameterType);
}

说明：通过参数标记的方式优先,如果没有则使用this.Binders.GetBinder(parameterDescriptor.ParameterType);

this.Binders的定义

protected internal ModelBinderDictionary Binders
{get{if (this._binders == null){this._binders = ModelBinders.Binders;}return this._binders;}set{this._binders = value;}
}

从上图可以看出，最终的绑定操作交给了ModelBinderDictionary（注意了，下面会接着讲）

正好我们回到前两章讲的ControllerActionInvoker,其中的参数绑定赋值过程GetParameterValues，如何获取的过程即绑定的过程

protected virtual object GetParameterValue(ControllerContext controllerContext, ParameterDescriptor parameterDescriptor)
{Type parameterType = parameterDescriptor.ParameterType;IModelBinder modelBinder = this.GetModelBinder(parameterDescriptor);IValueProvider valueProvider = controllerContext.Controller.ValueProvider;string modelName = parameterDescriptor.BindingInfo.Prefix ?? parameterDescriptor.ParameterName;Predicate<string> propertyFilter = ControllerActionInvoker.GetPropertyFilter(parameterDescriptor);ModelBindingContext bindingContext = new ModelBindingContext{FallbackToEmptyPrefix = parameterDescriptor.BindingInfo.Prefix == null,ModelMetadata = ModelMetadataProviders.Current.GetMetadataForType(null, parameterType),ModelName = modelName,ModelState = controllerContext.Controller.ViewData.ModelState,PropertyFilter = propertyFilter,ValueProvider = valueProvider};object obj = modelBinder.BindModel(controllerContext, bindingContext);return obj ?? parameterDescriptor.DefaultValue;
}

private IModelBinder GetModelBinder(ParameterDescriptor parameterDescriptor)
{return parameterDescriptor.BindingInfo.Binder ?? this.Binders.GetBinder(parameterDescriptor.ParameterType);
}

 this.Binders 其类型正好是ModelBinderDictionary（上面提到过），他的方法如下

    public IModelBinder GetBinder(Type modelType){return this.GetBinder(modelType, true);}/// <summary>Retrieves the model binder for the specified type or retrieves the default model binder.</summary>/// <returns>The model binder.</returns>/// <param name="modelType">The type of the model to retrieve.</param>/// <param name="fallbackToDefault">true to retrieve the default model binder.</param>/// <exception cref="T:System.ArgumentNullException">The <paramref name="modelType" /> parameter is null.</exception>public virtual IModelBinder GetBinder(Type modelType, bool fallbackToDefault){if (modelType == null){throw new ArgumentNullException("modelType");}return this.GetBinder(modelType, fallbackToDefault ? this.DefaultBinder : null);　　　　　　　//this.DefaultBinder 是下一章我们需要讲的内容。也是整个MVC核心的默认的绑定者}private IModelBinder GetBinder(Type modelType, IModelBinder fallbackBinder){IModelBinder modelBinder = this._modelBinderProviders.GetBinder(modelType);if (modelBinder != null){return modelBinder;}if (this._innerDictionary.TryGetValue(modelType, out modelBinder)){return modelBinder;}modelBinder = ModelBinders.GetBinderFromAttributes(modelType, () => string.Format(CultureInfo.CurrentCulture, MvcResources.ModelBinderDictionary_MultipleAttributes, new object[]{modelType.FullName}));return modelBinder ?? fallbackBinder;//DefaultBinder 很多情况下，前面的几个if都不会执行，所以使用系统默认的绑定者}

三、下一章接着介绍DefaultModelBinder

转载于:https://www.cnblogs.com/humble/p/3805565.html