asp.net mvc源码分析-Action篇 IModelBinder

我们首先还是看看ReflectedParameterBindingInfo的Binder属性吧：

public override IModelBinder Binder {
            get {
                IModelBinder binder = ModelBinders.GetBinderFromAttributes(_parameterInfo,
                    () => String.Format(CultureInfo.CurrentCulture, MvcResources.ReflectedParameterBindingInfo_MultipleConverterAttributes,
                        _parameterInfo.Name, _parameterInfo.Member));

                return binder;
            }
        }

在ModelBinders中有一个属性public static ModelBinderDictionary Binders，这个binders内容如下

ModelBinderDictionary binders =new ModelBinderDictionary(){
                { typeof(HttpPostedFileBase), new HttpPostedFileBaseModelBinder()},
                { typeof(byte[]), new ByteArrayModelBinder()},
                { typeof(Binary), new LinqBinaryModelBinder()}
            };
           说明默认的情况下就提供者3个Binder，但是这个属性是共有静态的，所以我们可以往里面添加自己的binder类，和前面文章讲的Filiter以及后面要讲的ValueProvider一样，

如在 Application_Start()方法中 ModelBinders.Binders.Add(xxx,xxxx)很不是很方便扩展了。

ModelBinders的GetBinderFromAttributes这个方法一看我们就能猜到它的逻辑了，

CustomModelBinderAttribute[] attrs = (CustomModelBinderAttribute[])element.GetCustomAttributes(typeof(CustomModelBinderAttribute), true /* inherit */);

获取当前参数的CustomModelBinderAttribute特性，如果有该特性就调用第一个特性的GetBinder()方法并返回其值，没有特性则返回null，如果有多个特性则抛出异常，说明一个参数上是不可以有多个CustomModelBinderAttribute特性的，正样 ReflectedParameterBindingInfo的binder属性就设置好了。

下面该轮到ControllerActionInvoker的Binders属性，

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

可以看到默认他返回的是ModelBinders.Binders。

接下来看看 IModelBinder binder = GetModelBinder(parameterDescriptor)这句究竟怎么返回的binder，

return parameterDescriptor.BindingInfo.Binder ?? Binders.GetBinder(parameterDescriptor.ParameterType);

太简单了，首先看看参数是否有binder特性，如果有就返回相应的binder，否者根据参数类型获取对应的binder。

其方法如下：

[csharp]
public IModelBinder GetBinder(Type modelType) {
          return GetBinder(modelType, true /* fallbackToDefault */);
      }

      public virtual IModelBinder GetBinder(Type modelType, bool fallbackToDefault) {
          if (modelType == null) {
              throw new ArgumentNullException("modelType");
          }

          return GetBinder(modelType, (fallbackToDefault) ? DefaultBinder : null);
      }

      private IModelBinder GetBinder(Type modelType, IModelBinder fallbackBinder) {

          // Try to look up a binder for this type. We use this order of precedence:
          // 1. Binder returned from provider
          // 2. Binder registered in the global table
          // 3. Binder attribute defined on the type
          // 4. Supplied fallback binder

          IModelBinder binder = _modelBinderProviders.GetBinder(modelType);
          if (binder != null) {
              return binder;
          }

          if (_innerDictionary.TryGetValue(modelType, out binder)) {
              return binder;
          }

          binder = ModelBinders.GetBinderFromAttributes(modelType,
              () => String.Format(CultureInfo.CurrentCulture, MvcResources.ModelBinderDictionary_MultipleAttributes, modelType.FullName));

          return binder ?? fallbackBinder;
      }

public IModelBinder GetBinder(Type modelType) {
return GetBinder(modelType, true /* fallbackToDefault */);
}

        public virtual IModelBinder GetBinder(Type modelType, bool fallbackToDefault) {
            if (modelType == null) {
                throw new ArgumentNullException("modelType");
            }

return GetBinder(modelType, (fallbackToDefault) ? DefaultBinder : null);
}

private IModelBinder GetBinde

补充：Web开发 , ASP.Net ,