[转载]Asp.net MVC源码分析 — 获取ModelBinder的优先级-Mikel

[转载]Asp.net MVC源码分析 — 获取ModelBinder的优先级 – 十一月的雨 – 博客园.

在ASP.NET mvc 框架中我们可以对System.Web.Mvc.Binders 进行扩展我们自定义的binder 类型，但是同时它还有一些其它的方法可以实现自定义的model binder.而且mvc在使用的时候还有一些策略,现分析如下:

获取ModelBinder 对象的入口方法是GetParameterValue, 其中

IModelBinder binder = GetModelBinder(parameterDescriptor);

这一句代码决定了ModelBinder 的使用策略。

System.Web.Mvc.ControllerActionInvoker

01
protected virtual object GetParameterValue(ControllerContext controllerContext, ParameterDescriptor parameterDescriptor) { 

02
 // collect all of the necessary binding properties 

03
 Type parameterType = parameterDescriptor.ParameterType; 

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 //Hey 请过来获取binder 的入口在这里，csdn 代段没法加高亮，垃极啊~! 

05
 IModelBinder binder = GetModelBinder(parameterDescriptor); 

06
 IValueProvider valueProvider = controllerContext.Controller.ValueProvider; 

07
 string parameterName = parameterDescriptor.BindingInfo.Prefix ?? parameterDescriptor.ParameterName; 

08
 Predicate<string> propertyFilter = GetPropertyFilter(parameterDescriptor); 

09
 
10
 // finally, call into the binder 

11
 ModelBindingContext bindingContext = new ModelBindingContext() { 

12
 FallbackToEmptyPrefix = (parameterDescriptor.BindingInfo.Prefix == null), // only fall back if prefix not specified 

13
 ModelMetadata = ModelMetadataProviders.Current.GetMetadataForType(null, parameterType), 

14
 ModelName = parameterName, 

15
 ModelState = controllerContext.Controller.ViewData.ModelState, 

16
 PropertyFilter = propertyFilter, 

17
 ValueProvider = valueProvider 

18
 }; 

19
 
20
 object result = binder.BindModel(controllerContext, bindingContext); 

21
 return result ?? parameterDescriptor.DefaultValue; 

22
 } 

23

24
private IModelBinder GetModelBinder(ParameterDescriptor parameterDescriptor) { 

25
 // look on the parameter itself, then look in the global table 

26
 return parameterDescriptor.BindingInfo.Binder ?? Binders.GetBinder(parameterDescriptor.ParameterType); 

27
 }

这里优先从 parameterDescriptor.BindingInfo中得到IModelBinder, 接下来我们看一下怎么从parameterDescriptor中获取binder

首先找到 ReflectedActionDescriptor对象,可以看到在GetParameters方法中生成了ReflectedParameterDescriptor 对象，

System.Web.Mvc.ReflectedActionDescriptor

01
public override ParameterDescriptor[] GetParameters() { 

02
 ParameterDescriptor[] parameters = LazilyFetchParametersCollection(); 

03
 
04
 // need to clone array so that user modifications aren't accidentally stored 

05
 return (ParameterDescriptor[])parameters.Clone(); 

06
 } 

07
view plain

08
private ParameterDescriptor[] LazilyFetchParametersCollection() { 

09
 return DescriptorUtil.LazilyFetchOrCreateDescriptors<ParameterInfo, ParameterDescriptor>( 

10
 ref _parametersCache /* cacheLocation */, 

11
 MethodInfo.GetParameters /* initializer */, 

12
 parameterInfo => new ReflectedParameterDescriptor(parameterInfo, this) /* converter */); 

13
 }

这个对象中调用了ModelBinders.GetBinderFromAttributes方法来获取binder

ReflectedParameterDescriptor -> ReflectedParameterBindingInfo

1
public override IModelBinder Binder { 

2
 get { 

3
 IModelBinder binder = ModelBinders.GetBinderFromAttributes(_parameterInfo, 

4
 () => String.Format(CultureInfo.CurrentCulture, MvcResources.ReflectedParameterBindingInfo_MultipleConverterAttributes, 

5
 _parameterInfo.Name, _parameterInfo.Member)); 

6
 
7
 return binder; 

8
 } 

9
 }

System.Web.Mvc.ModelBinders

1
internal static IModelBinder GetBinderFromAttributes(ICustomAttributeProvider element, Func<string> 

2
 errorMessageAccessor) { 

3
CustomModelBinderAttribute[] attrs = (CustomModelBinderAttribute[])element. 

4
GetCustomAttributes(typeof(CustomModelBinderAttribute), 

5
true /* inherit */); 

6
 
7
return GetBinderFromAttributesImpl(attrs, errorMessageAccessor); 

8
 }

接下来我们看

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

语句后面的的分支.

System.Web.Mvc.ModelBinderDictionary

01
private IModelBinder GetBinder(Type modelType, IModelBinder fallbackBinder) { 

02
 
03
 // Try to look up a binder for this type. We use this order of precedence: 

04
 // 1. Binder returned from provider 

05
 // 2. Binder registered in the global table 

06
 // 3. Binder attribute defined on the type 

07
 // 4. Supplied fallback binder 

08
 
09
 IModelBinder binder = _modelBinderProviders.GetBinder(modelType); 

10
 if (binder != null) { 

11
 return binder; 

12
 } 

13
 
14
 if (_innerDictionary.TryGetValue(modelType, out binder)) { 

15
 return binder; 

16
 } 

17
 
18
 binder = ModelBinders.GetBinderFromAttributes(modelType, 

19
 ()  => String.Format(CultureInfo.CurrentCulture,  MvcResources.ModelBinderDictionary_MultipleAttributes,  modelType.FullName)); 

20
 
21
 return binder ?? fallbackBinder; 

22
 } 

23

24
internal static IModelBinder GetBinderFromAttributes(Type type, Func<string> errorMessageAccessor) { 

25
 AttributeCollection allAttrs = TypeDescriptorHelper.Get(type).GetAttributes(); 

26
 CustomModelBinderAttribute[] filteredAttrs = allAttrs.OfType<CustomModelBinderAttribute>().ToArray(); 

27
 return GetBinderFromAttributesImpl(filteredAttrs, errorMessageAccessor); 

28
 }

到这里我们就清楚的知道了获取IModelBinder的优先级。

结论:

1.如果在Action参数中的对象中标记了元数据的IModelBinder 实现时则调用该实现。//注:如果这句不理解可以继续看下面的实例

2.如果在参数中没有标记元数据的IModelBinder 实现 ,则调用的优先顺序为:

// (1).从全局的ModelBinderProviders.BinderProviders 中查找，我们也可以注册自己的provider
// (2).从全局的System.Web.Mvc.Binders 对象中查找，自己也可以注册自己的binder
// (3). 从参数对象的类型中的attribute 找到 ModelBinderAtribute中的IModelBinder 实现.
// (4). 最后如果经过以上步骤都没有找到IModelBinder的实现的话，就用MVC默认的实现DefaultModelBinder类,

1
public virtual IModelBinder GetBinder(Type modelType, bool fallbackToDefault) { 

2
 if (modelType == null) { 

3
 throw new ArgumentNullException("modelType"); 

4
 } 

5
 
6
 return GetBinder(modelType, (fallbackToDefault) ? DefaultBinder : null); 

7
 }

示例代码:

下面我们通过实例代码来印证以上的结论。

01
//Model 类:

02
public class FormTestModel 

03
 { 

04
 [Required] 

05
 [DataType(DataType.Text)] 

06
 [Display(Name = "Room Name")] 

07
 public string RoomName { get; set; } 

08
 
09
 [Required] 

10
 [DataType(DataType.Text)] 

11
 [Display(Name = "Room Count")] 

12
 public string RoomCount { get; set; } 

13
 
14
 } 

15

16
//Action类:

17
[HttpPost] 

18
 public ActionResult FormTest(FormTestModels model, string returnUrl) 

19
 { 

20
 <span style="white-space:pre">    </span>return view(); 

21
 } 

22

23
//我们新建四个IModelBinder 的实现;

24
internal sealed class FormTestModelBinderImpl1 : IModelBinder 

25
 { 

26
 public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext) 

27
 { 

28
 DefaultModelBinder defBinder = new DefaultModelBinder(); 

29
 return defBinder.BindModel(controllerContext, bindingContext); 

30
 } 

31
 } 

32
 internal sealed class FormTestModelBinderImpl2 : IModelBinder 

33
 { 

34
 public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext) 

35
 { 

36
 DefaultModelBinder defBinder = new DefaultModelBinder(); 

37
 return defBinder.BindModel(controllerContext, bindingContext); 

38
 } 

39
 } 

40
 internal sealed class FormTestModelBinderImpl3 : IModelBinder 

41
 { 

42
 public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext) 

43
 { 

44
 DefaultModelBinder defBinder = new DefaultModelBinder(); 

45
 return defBinder.BindModel(controllerContext, bindingContext); 

46
 } 

47
 } 

48
 internal sealed class FormTestModelBinderImpl4 : IModelBinder 

49
 { 

50
 public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext) 

51
 { 

52
 DefaultModelBinder defBinder = new DefaultModelBinder(); 

53
 return defBinder.BindModel(controllerContext, bindingContext); 

54
 } 

55
 } 

56
 
57
 public sealed class FormTestModelBinderProviderImpl : IModelBinderProvider 

58
 { 

59
 public IModelBinder GetBinder(Type modelType) 

60
 { 

61
 if (modelType == typeof(FormTestModels)) 

62
 { 

63
 //"provider implementition"; 

64
 return new FormTestModelsModelBinderImpl2(); 

65
 } 

66
 
67
 return null; 

68
 } 

69
 }

01
然后我们分别加入:

02
//第一优先:

03
[HttpPost] 

04
 public ActionResult FormTest([ModelBinder(typeof(FormTestModelBinderImpl1))] FormTestModel model, string returnUrl) 

05
 { 

06
 return view(); 

07
 } 

08

09
//第二优先:

10
ModelBinderProviders.BinderProviders.Add(new FormTestModelBinderProviderImpl2()); 

11
//第三优先:

12
System.Web.Mvc.ModelBinders.Binders[typeof(FormTestModel)] = new FormTestModelBinderImpl3();

1
//第四优先:

2
 [ModelBinder(typeof(FormTestModelBinderImpl4))] 

3
 public class FormTestModel 

4
 { 

5
//codes 

6
}

最后我们在四个binder上面设置断点，看一下代码执行的情况，就可以清楚的看到我们的结论是多么的无比正确.:)

最后感谢大家观看，以上分析如有雷同纯属巧合。

谢谢大家。

后记:

其它的相关文章:

MVC运行机制之源码剖析http://blog.csdn.net/study_live/article/details/4871745

[转载]Asp.net MVC源码分析 -- 获取ModelBinder的优先级

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