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ASP.NET MVC5学习笔记之Action参数模型绑定值提供体系

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　　这一节我们关注模型绑定的值提供体系，先来介绍几个重要的接口

一. IValueProvider，接口定义如下:

            1
            public
            interface
             IValueProvider

            2
                {

            3
            4
            bool ContainsPrefix(string prefix);
56         ValueProviderResult GetValue(string key);
7     }

从上面可以看出，IValueProvider定义了两个方法， 一个是检测是否包含指定的前缀，一个是通过指定的Key获取查询结果.这里前缀的概念主要是针对复杂类型的绑定，复杂类型包含属性，而属性的类型又是一个复杂类型，这样一层层下来，当我们在绑定类型的属性时，我们必须有一种机制确定该属性的值是从属于某个对象的，这就有了前缀的概念。系统定义了以下几种类型的绑定语法:

1.简单类型

　　prefix == 变量的名称

2. 复杂类型

　　prefix 变量名称

　　prefix.Name

　　prefix.Address.Name

3. 数组

　　a. 同名数据项

　　　　多个同名数据项， ValueProviderResult直接转换成数组

　　b. 基于索引的数组绑定

　　　　[0].Name

　　　　[0].PhoneNo

　　　　[0].Email

　　　　[1].Name

　　　　[1].PhoneNo

　　　　[1].Email

4，集合IEnumerable<T> 与数组类似

5. 字典

　　[0].Key

　　[0].Value.Name

　　[0].Value.EmailAddress

　　[1].Key

　　[2].Value.Name

　　[3].Value.EmailAddress

 二. ValueProviderResult类型

             1
             [Serializable]

             2
            public
            class
             ValueProviderResult

             3
                {

             4
            protected
             ValueProviderResult();

             5
             6
            public ValueProviderResult(object rawValue, string attemptedValue, CultureInfo culture);
 7 8publicstring AttemptedValue { get; protectedset; }
 910public CultureInfo Culture { get; protectedset; }
1112publicobject RawValue { get; protectedset; }
1314publicobject ConvertTo(Type type);
1516publicvirtualobject ConvertTo(Type type, CultureInfo culture);
17     }

   AttemptedValue表示从值的字符串表示，RawValue 表示值的原始值. 同时看到定义类型转换接口。 这里转换的代码值得研究一下:

             1
            public
            virtual
            object
             ConvertTo(Type type, CultureInfo culture)

             2
                    {

             3
            if (type == null)
 4            {
 5thrownew ArgumentNullException("type");
 6            }
 7 8             CultureInfo cultureToUse = culture ?? Culture;
 9return UnwrapPossibleArrayType(cultureToUse, RawValue, type);
10        }
1112privatestaticobject UnwrapPossibleArrayType(CultureInfo culture, object value, Type destinationType)
13        {
14if (value == null || destinationType.IsInstanceOfType(value))
15            {
16return value;
17            }
1819// array conversion results in four cases, as below20             Array valueAsArray = value as Array;
21if (destinationType.IsArray)
22            {
23                 Type destinationElementType = destinationType.GetElementType();
24if (valueAsArray != null)
25                {
26// case 1: both destination + source type are arrays, so convert each element27                     IList converted = Array.CreateInstance(destinationElementType, valueAsArray.Length);
28for (int i = 0; i < valueAsArray.Length; i++)
29                    {
30                         converted[i] = ConvertSimpleType(culture, valueAsArray.GetValue(i), destinationElementType);
31                    }
32return converted;
33                }
34else35                {
36// case 2: destination type is array but source is single element, so wrap element in array + convert37object element = ConvertSimpleType(culture, value, destinationElementType);
38                     IList converted = Array.CreateInstance(destinationElementType, 1);
39                     converted[0] = element;
40return converted;
41                }
42            }
43elseif (valueAsArray != null)
44            {
45// case 3: destination type is single element but source is array, so extract first element + convert46if (valueAsArray.Length > 0)
47                {
48                     value = valueAsArray.GetValue(0);
49return ConvertSimpleType(culture, value, destinationType);
50                }
51else52                {
53// case 3(a): source is empty array, so can‘t perform conversion54returnnull;
55                }
56            }
57// case 4: both destination + source type are single elements, so convert58return ConvertSimpleType(culture, value, destinationType);
59         }

 1. 如果值是目标类型的实例，直接返回

 2. 尝试转换为数组，这里列了4种情况。

 3. 单一类型转换

 再来看一下ConvertSimpleType的代码:

             1
            private
            static
            object ConvertSimpleType(CultureInfo culture, object value, Type destinationType)
 2        {
 3if (value == null || destinationType.IsInstanceOfType(value))
 4            {
 5return value;
 6            }
 7 8// if this is a user-input value but the user didn‘t type anything, return no value 9string valueAsString = value asstring;
10if (valueAsString != null && String.IsNullOrWhiteSpace(valueAsString))
11            {
12returnnull;
13            }
1415// In case of a Nullable object, we extract the underlying type and try to convert it.16             Type underlyingType = Nullable.GetUnderlyingType(destinationType);
1718if (underlyingType != null)
19            {
20                 destinationType = underlyingType;
21            }
2223// String doesn‘t provide convertibles to interesting types, and thus it will typically throw rather than succeed.24if (valueAsString == null)
25            {
26// If the source type implements IConvertible, try that first27                 IConvertible convertible = value as IConvertible;
28if (convertible != null)
29                {
30try31                    {
32return convertible.ToType(destinationType, culture);
33                    }
34catch35                    {
36                    }
37                }
38            }
3940// Last resort, look for a type converter41             TypeConverter converter = TypeDescriptor.GetConverter(destinationType);
42bool canConvertFrom = converter.CanConvertFrom(value.GetType());
43if (!canConvertFrom)
44            {
45                 converter = TypeDescriptor.GetConverter(value.GetType());
46            }
47if (!(canConvertFrom || converter.CanConvertTo(destinationType)))
48            {
49// EnumConverter cannot convert integer, so we verify manually50if (destinationType.IsEnum && value isint)
51                {
52return Enum.ToObject(destinationType, (int)value);
53                }
5455string message = String.Format(CultureInfo.CurrentCulture, MvcResources.ValueProviderResult_NoConverterExists,
56                                               value.GetType().FullName, destinationType.FullName);
57thrownew InvalidOperationException(message);
58            }
5960try61            {
62object convertedValue = (canConvertFrom)
63                                             ? converter.ConvertFrom(null/* context */, culture, value)
64                                             : converter.ConvertTo(null/* context */, culture, value, destinationType);
65return convertedValue;
66            }
67catch (Exception ex)
68            {
69string message = String.Format(CultureInfo.CurrentCulture, MvcResources.ValueProviderResult_ConversionThrew,
70                                               value.GetType().FullName, destinationType.FullName);
71thrownew InvalidOperationException(message, ex);
72            }
73         }

　　这里也考虑了几种情况转换
1. 值是目标类型的实例直接返回
2. 值是空串返回null
3. 可空类型取其下的真正类型
4. 尝试利用IConvertible转换
5. 利用目标类型和值类型的TypeConverter
6. 检查目标类型是Enum和值类型是否int

 三. ValueProviderFactory 

            public
            abstract
            class
             ValueProviderFactory
    {
        
            public
            abstract
             IValueProvider GetValueProvider(ControllerContext controllerContext);
    }

表示的值提供对象的创健工厂.

四. ValueProvider创建工厂和具体ValueProvider介绍

 ValueProvider的调用入口是Controller.ValueProvider属性，它是调用ValueProviderFactories.Factories.GetValueProvider()返回值,看看ValueProviderFactories的定义

             1
            public
            static
            class
             ValueProviderFactories

             2
                {

             3
            private
            static
            readonly ValueProviderFactoryCollection _factories = new ValueProviderFactoryCollection()
 4        {
 5new ChildActionValueProviderFactory(),
 6new FormValueProviderFactory(),
 7new JsonValueProviderFactory(),
 8new RouteDataValueProviderFactory(),
 9new QueryStringValueProviderFactory(),
10new HttpFileCollectionValueProviderFactory(),
11        };
1213publicstatic ValueProviderFactoryCollection Factories
14        {
15get { return _factories; }
16        }
17     }

可以了解到系统内置几种ValueProviderFactory, 下面依次来了解.

a. ChildActionValueProviderFactory 创建ChildActionValueProvider， 提供在HtmlHelper.Action方法附加的路由信息

                 1
                public
                sealed
                class
                 ChildActionValueProviderFactory : ValueProviderFactory

                 2
                    {

                 3
                public
                override
                 IValueProvider GetValueProvider(ControllerContext controllerContext)

                 4
                        {

                 5
                if (controllerContext == null)
 6            {
 7thrownew ArgumentNullException("controllerContext");
 8            }
 910returnnew ChildActionValueProvider(controllerContext);
11        }
12     }
View Code

b. FormValueProviderFactory 创建FormValueProvider , 提供请求表单的值

                 1
                public
                sealed
                class
                 FormValueProviderFactory : ValueProviderFactory

                 2
                    {

                 3
                private
                readonly
                 UnvalidatedRequestValuesAccessor _unvalidatedValuesAccessor;

                 4
                 5
                public
                 FormValueProviderFactory()

                 6             : this(null)
 7        {
 8        }
 910// For unit testing11internal FormValueProviderFactory(UnvalidatedRequestValuesAccessor unvalidatedValuesAccessor)
12        {
13             _unvalidatedValuesAccessor = unvalidatedValuesAccessor ?? (cc => new UnvalidatedRequestValuesWrapper(cc.HttpContext.Request.Unvalidated));
14        }
1516publicoverride IValueProvider GetValueProvider(ControllerContext controllerContext)
17        {
18if (controllerContext == null)
19            {
20thrownew ArgumentNullException("controllerContext");
21            }
2223returnnew FormValueProvider(controllerContext, _unvalidatedValuesAccessor(controllerContext));
24        }
25     }
View Code

c. JsonValueProviderFactory 处理json请求类型(application/json)， 创建DictionaryValueProvider，

                  1
                public
                sealed
                class
                 JsonValueProviderFactory : ValueProviderFactory

                  2
                    {

                  3
                private
                static
                void AddToBackingStore(EntryLimitedDictionary backingStore, string prefix, object value)
  4        {
  5             IDictionary<string, object> d = value as IDictionary<string, object>;
  6if (d != null)
  7            {
  8foreach (KeyValuePair<string, object> entry in d)
  9                {
 10                    AddToBackingStore(backingStore, MakePropertyKey(prefix, entry.Key), entry.Value);
 11                }
 12return;
 13            }
 14 15             IList l = value as IList;
 16if (l != null)
 17            {
 18for (int i = 0; i < l.Count; i++)
 19                {
 20                    AddToBackingStore(backingStore, MakeArrayKey(prefix, i), l[i]);
 21                }
 22return;
 23            }
 24 25// primitive 26            backingStore.Add(prefix, value);
 27        }
 28 29privatestaticobject GetDeserializedObject(ControllerContext controllerContext)
 30        {
 31if (!controllerContext.HttpContext.Request.ContentType.StartsWith("application/json", StringComparison.OrdinalIgnoreCase))
 32            {
 33// not JSON request 34returnnull;
 35            }
 36 37             StreamReader reader = new StreamReader(controllerContext.HttpContext.Request.InputStream);
 38string bodyText = reader.ReadToEnd();
 39if (String.IsNullOrEmpty(bodyText))
 40            {
 41// no JSON data 42returnnull;
 43            }
 44 45             JavaScriptSerializer serializer = new JavaScriptSerializer();
 46object jsonData = serializer.DeserializeObject(bodyText);
 47return jsonData;
 48        }
 49 50publicoverride IValueProvider GetValueProvider(ControllerContext controllerContext)
 51        {
 52if (controllerContext == null)
 53            {
 54thrownew ArgumentNullException("controllerContext");
 55            }
 56 57object jsonData = GetDeserializedObject(controllerContext);
 58if (jsonData == null)
 59            {
 60returnnull;
 61            }
 62 63             Dictionary<string, object> backingStore = new Dictionary<string, object>(StringComparer.OrdinalIgnoreCase);
 64             EntryLimitedDictionary backingStoreWrapper = new EntryLimitedDictionary(backingStore);
 65            AddToBackingStore(backingStoreWrapper, String.Empty, jsonData);
 66returnnew DictionaryValueProvider<object>(backingStore, CultureInfo.CurrentCulture);
 67        }
 68 69privatestaticstring MakeArrayKey(string prefix, int index)
 70        {
 71return prefix + "[" + index.ToString(CultureInfo.InvariantCulture) + "]";
 72        }
 73 74privatestaticstring MakePropertyKey(string prefix, string propertyName)
 75        {
 76return (String.IsNullOrEmpty(prefix)) ? propertyName : prefix + "." + propertyName;
 77        }
 78 79privateclass EntryLimitedDictionary
 80        {
 81privatestaticint _maximumDepth = GetMaximumDepth();
 82privatereadonly IDictionary<string, object> _innerDictionary;
 83privateint _itemCount = 0;
 84 85public EntryLimitedDictionary(IDictionary<string, object> innerDictionary)
 86            {
 87                 _innerDictionary = innerDictionary;
 88            }
 89 90publicvoid Add(string key, object value)
 91            {
 92if (++_itemCount > _maximumDepth)
 93                {
 94thrownew InvalidOperationException(MvcResources.JsonValueProviderFactory_RequestTooLarge);
 95                }
 96 97                _innerDictionary.Add(key, value);
 98            }
 99100privatestaticint GetMaximumDepth()
101            {
102                 NameValueCollection appSettings = ConfigurationManager.AppSettings;
103if (appSettings != null)
104                {
105string[] valueArray = appSettings.GetValues("aspnet:MaxJsonDeserializerMembers");
106if (valueArray != null && valueArray.Length > 0)
107                    {
108int result;
109if (Int32.TryParse(valueArray[0], out result))
110                        {
111return result;
112                        }
113                    }
114                }
115116return1000; // Fallback default117            }
118        }
119     }
View Code

d. RouteDataValueProviderFactory 创建RouteDataValueProvider, 提供路由信息相关值

                 1
                public
                sealed
                class
                 RouteDataValueProviderFactory : ValueProviderFactory

                 2
                    {

                 3
                public
                override
                 IValueProvider GetValueProvider(ControllerContext controllerContext)

                 4
                        {

                 5
                if (controllerContext == null)
 6            {
 7thrownew ArgumentNullException("controllerContext");
 8            }
 910returnnew RouteDataValueProvider(controllerContext);
11        }
12     }
View Code

e. QueryStringValueProviderFactory 创建QueryStringValueProvider, 提供查询字符串值

                 1
                public
                sealed
                class
                 QueryStringValueProviderFactory : ValueProviderFactory

                 2
                    {

                 3
                private
                readonly
                 UnvalidatedRequestValuesAccessor _unvalidatedValuesAccessor;

                 4
                 5
                public
                 QueryStringValueProviderFactory()

                 6             : this(null)
 7        {
 8        }
 910// For unit testing11internal QueryStringValueProviderFactory(UnvalidatedRequestValuesAccessor unvalidatedValuesAccessor)
12        {
13             _unvalidatedValuesAccessor = unvalidatedValuesAccessor ?? (cc => new UnvalidatedRequestValuesWrapper(cc.HttpContext.Request.Unvalidated));
14        }
1516publicoverride IValueProvider GetValueProvider(ControllerContext controllerContext)
17        {
18if (controllerContext == null)
19            {
20thrownew ArgumentNullException("controllerContext");
21            }
2223returnnew QueryStringValueProvider(controllerContext, _unvalidatedValuesAccessor(controllerContext));
24        }
25     }
View Code

f. HttpFileCollectionValueProviderFactory创建HttpFileCollectionValueProvider上传文件值提供

                 1
                public
                sealed
                class
                 HttpFileCollectionValueProviderFactory : ValueProviderFactory

                 2
                    {

                 3
                public
                override
                 IValueProvider GetValueProvider(ControllerContext controllerContext)

                 4
                        {

                 5
                if (controllerContext == null)
 6            {
 7thrownew ArgumentNullException("controllerContext");
 8            }
 910returnnew HttpFileCollectionValueProvider(controllerContext);
11        }
12     }
View Code

 整体ValueProvider的继承体系统如下图:

原文：http://www.cnblogs.com/jjyjjyjjy/p/3730161.html

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