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 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;
        }
这里需要注意binder选着的优先顺序，（1）从_modelBinderProviders里面找相应的binder

private ModelBinderProviderCollection _modelBinderProviders;
        public ModelBinderDictionary()
            : this(ModelBinderProviders.BinderProviders) {
        }
        internal ModelBinderDictionary(ModelBinderProviderCollection modelBinderProviders) {
            _modelBinderProviders = modelBinderProviders;
        }

public static class ModelBinderProviders {
        private readonly static ModelBinderProviderCollection _binderProviders = new ModelBinderProviderCollection {
        };
        public static ModelBinderProviderCollection BinderProviders {
            get {
                return _binderProviders;
            }
        }
    }

从这些代码我们可以得知 默认情况下_modelBinderProviders里面是没有数据 ，那么什么时候这个集合有数据了，当我们在Application_Start()中调用ModelBinderProviders.BinderProviders.Add(xxx)就有数据了，

（2）从_innerDictionary中取数据，这个数据时什么时候添加上去的了，看了ModelBinderDictionary的add放就明白了

public void Add(Type key, IModelBinder value) {
            _innerDictionary.Add(key, value);
        }

其实 ModelBinderDictionary内部很多方法都是围绕着_innerDictionary集合操作的。

（3）从参数数据类型上获取binder

（4）返货默认的DefaultBinder，该属性默认= new DefaultModelBinder()

现在 我们可以总结一下binder的优先顺序（1）参数上的CustomModelBinderAttribute特性；（2）ModelBinderProviders.BinderProviders.Add(xxx)注册的IModelBinderProvider；（3）ModelBinders的Binders；（4）参数类型上的CustomModelBinderAttribute特性；（5）返回默认的DefaultModelBinder

IValueProvider valueProvider = controllerContext.Controller.ValueProvider; 这句的讲解我们放到后面的文章中吧，

string parameterName = parameterDescriptor.BindingInfo.Prefix ?? parameterDescriptor.ParameterName;这句获取参数名称，

Predicate<string> propertyFilter = GetPropertyFilter(parameterDescriptor);这个就只控制该参数时候需要绑定对应的值。

private static Predicate<string> GetPropertyFilter(ParameterDescriptor parameterDescriptor) {
            ParameterBindingInfo bindingInfo = parameterDescriptor.BindingInfo;
            return propertyName => BindAttribute.IsPropertyAllowed(propertyName, bindingInfo.Include.ToArray(), bindingInfo.Exclude.ToArray());
        }

BindAttribute.IsPropertyAllowed如下：

internal static bool IsPropertyAllowed(string propertyName, string[] includeProperties, string[] excludeProperties) {
            // We allow a property to be bound if its both in the include list AND not in the exclude list.
            // An empty include list implies all properties are allowed.
            // An empty exclude list implies no properties are disallowed.
            bool includeProperty = (includeProperties == null) || (includeProperties.Length == 0) || includeProperties.Contains(propertyName, StringComparer.OrdinalIgnoreCase);
            bool excludeProperty = (excludeProperties != null) && excludeProperties.Contains(propertyName, StringComparer.OrdinalIgnoreCase);
            return includeProperty && !excludeProperty;
        }

现在 终于看到了BindAttribute在申明地方用到了。

现在 我们来做一个自定的ModelBinder类怎么做。

[csharp]
public class UserInfo 
    { 
        public string Name { set; get; } 
        public string Age { set; get; } 
    } 
    public class UserInfoModelBinder : IModelBinder 
    { 
        public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext) 
        { 
            object obj = Activator.CreateInstance(bindingContext.ModelType); 
            foreach (PropertyInfo p in bindingContext.ModelType.GetProperties()) 
            { 
               ValueProviderResult vpResult=  bindingContext.ValueProvider.GetValue(p.Name); 
               if (vpResult != null) 
               { 
                   object value = vpResult.ConvertTo(p.PropertyType); 
                   p.SetValue(obj, value, null); 
               } 
            } 
            return obj; 
        } 
    } 
    public class HomeController : Controller 
    { 
 
        public ActionResult Index([ModelBinder(typeof(UserInfoModelBinder))]UserInfo userInfo) 
        { 
            return Content("Name:" + userInfo.Name + " Age:" + userInfo.Age); 
          //  return View();  
 
        } 
   }

public class UserInfo
    {
        public string Name { set; get; }
        public string Age { set; get; }
    }
    public class UserInfoModelBinder : IModelBinder
    {
        public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
        {
            object obj = Activator.CreateInstance(bindingContext.ModelType);
            foreach (PropertyInfo p in bindingContext.ModelType.GetProperties())
            {
               ValueProviderResult vpResult=  bindingContext.ValueProvider.GetValue(p.Name);
               if (vpResult != null)
               {
                   object value = vpResult.ConvertTo(p.PropertyType);
                   p.SetValue(obj, value, null);
               }
            }
            return obj;
        }
    }
    public class HomeController : Controller
    {

public ActionResult Index([ModelBinder(typeof(UserInfoModelBinder))]UserInfo userInfo)
        {
            return Content("Name:" + userInfo.Name + " Age:" + userInfo.Age);
          //  return View();

}
   }运行结果如图：