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一、特性是什么?
特性是可以添加到编程元素(例如程序集、类型、成员和参数)的注释。 它们存储在程序集的元数据中,可以在运行时使用反射 API 时访问。
F12我们可以查看Attribute的定义
#region 程序集 mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089 // C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.5\mscorlib.dll #endregion using System.Reflection; using System.Runtime.InteropServices; using System.Security; namespace System { // // 摘要: // Represents the base class for custom attributes. [AttributeUsageAttribute(AttributeTargets.All, Inherited = true, AllowMultiple = false)] [ClassInterfaceAttribute(ClassInterfaceType.None)] [ComDefaultInterfaceAttribute(typeof(_Attribute))] [ComVisibleAttribute(true)] public abstract class Attribute : _Attribute { // // 摘要: // Initializes a new instance of the System.Attribute class. protected Attribute(); // // 摘要: // When implemented in a derived class, gets a unique identifier for this System.Attribute. // // 返回结果: // An System.Object that is a unique identifier for the attribute. public virtual object TypeId { get; } // // 摘要: // Retrieves a custom attribute applied to a specified assembly. Parameters specify // the assembly and the type of the custom attribute to search for. // // 参数: // element: // An object derived from the System.Reflection.Assembly class that describes a // reusable collection of modules. // // attributeType: // The type, or a base type, of the custom attribute to search for. // // 返回结果: // A reference to the single custom attribute of type attributeType that is applied // to element, or null if there is no such attribute. // // 异常: // T:System.ArgumentNullException: // element or attributeType is null. // // T:System.ArgumentException: // attributeType is not derived from System.Attribute. // // T:System.Reflection.AmbiguousMatchException: // More than one of the requested attributes was found. public static Attribute GetCustomAttribute(Assembly element, Type attributeType); // // 摘要: // Retrieves a custom attribute applied to a member of a type. Parameters specify // the member, and the type of the custom attribute to search for. // // 参数: // element: // An object derived from the System.Reflection.MemberInfo class that describes // a constructor, event, field, method, or property member of a class. // // attributeType: // The type, or a base type, of the custom attribute to search for. // // 返回结果: // A reference to the single custom attribute of type attributeType that is applied // to element, or null if there is no such attribute. // // 异常: // T:System.ArgumentNullException: // element or attributeType is null. // // T:System.ArgumentException: // attributeType is not derived from System.Attribute. // // T:System.NotSupportedException: // element is not a constructor, method, property, event, type, or field. // // T:System.Reflection.AmbiguousMatchException: // More than one of the requested attributes was found. // // T:System.TypeLoadException: // A custom attribute type cannot be loaded. public static Attribute GetCustomAttribute(MemberInfo element, Type attributeType); // // 摘要: // Retrieves a custom attribute applied to a module. Parameters specify the module, // and the type of the custom attribute to search for. // // 参数: // element: // An object derived from the System.Reflection.Module class that describes a portable // executable file. // // attributeType: // The type, or a base type, of the custom attribute to search for. // // 返回结果: // A reference to the single custom attribute of type attributeType that is applied // to element, or null if there is no such attribute. // // 异常: // T:System.ArgumentNullException: // element or attributeType is null. // // T:System.ArgumentException: // attributeType is not derived from System.Attribute. // // T:System.Reflection.AmbiguousMatchException: // More than one of the requested attributes was found. public static Attribute GetCustomAttribute(Module element, Type attributeType); // // 摘要: // Retrieves a custom attribute applied to a method parameter. Parameters specify // the method parameter, and the type of the custom attribute to search for. // // 参数: // element: // An object derived from the System.Reflection.ParameterInfo class that describes // a parameter of a member of a class. // // attributeType: // The type, or a base type, of the custom attribute to search for. // // 返回结果: // A reference to the single custom attribute of type attributeType that is applied // to element, or null if there is no such attribute. // // 异常: // T:System.ArgumentNullException: // element or attributeType is null. // // T:System.ArgumentException: // attributeType is not derived from System.Attribute. // // T:System.Reflection.AmbiguousMatchException: // More than one of the requested attributes was found. // // T:System.TypeLoadException: // A custom attribute type cannot be loaded. public static Attribute GetCustomAttribute(ParameterInfo element, Type attributeType); // // 摘要: // Retrieves a custom attribute applied to an assembly. Parameters specify the assembly, // the type of the custom attribute to search for, and an ignored search option. // // 参数: // element: // An object derived from the System.Reflection.Assembly class that describes a // reusable collection of modules. // // attributeType: // The type, or a base type, of the custom attribute to search for. // // inherit: // This parameter is ignored, and does not affect the operation of this method. // // 返回结果: // A reference to the single custom attribute of type attributeType that is applied // to element, or null if there is no such attribute. // // 异常: // T:System.ArgumentNullException: // element or attributeType is null. // // T:System.ArgumentException: // attributeType is not derived from System.Attribute. // // T:System.Reflection.AmbiguousMatchException: // More than one of the requested attributes was found. public static Attribute GetCustomAttribute(Assembly element, Type attributeType, bool inherit); // // 摘要: // Retrieves a custom attribute applied to a member of a type. Parameters specify // the member, the type of the custom attribute to search for, and whether to search // ancestors of the member. // // 参数: // element: // An object derived from the System.Reflection.MemberInfo class that describes // a constructor, event, field, method, or property member of a class. // // attributeType: // The type, or a base type, of the custom attribute to search for. // // inherit: // If true, specifies to also search the ancestors of element for custom attributes. // // 返回结果: // A reference to the single custom attribute of type attributeType that is applied // to element, or null if there is no such attribute. // // 异常: // T:System.ArgumentNullException: // element or attributeType is null. // // T:System.ArgumentException: // attributeType is not derived from System.Attribute. // // T:System.NotSupportedException: // element is not a constructor, method, property, event, type, or field. // // T:System.Reflection.AmbiguousMatchException: // More than one of the requested attributes was found. // // T:System.TypeLoadException: // A custom attribute type cannot be loaded. public static Attribute GetCustomAttribute(MemberInfo element, Type attributeType, bool inherit); // // 摘要: // Retrieves a custom attribute applied to a module. Parameters specify the module, // the type of the custom attribute to search for, and an ignored search option. // // 参数: // element: // An object derived from the System.Reflection.Module class that describes a portable // executable file. // // attributeType: // The type, or a base type, of the custom attribute to search for. // // inherit: // This parameter is ignored, and does not affect the operation of this method. // // 返回结果: // A reference to the single custom attribute of type attributeType that is applied // to element, or null if there is no such attribute. // // 异常: // T:System.ArgumentNullException: // element or attributeType is null. // // T:System.ArgumentException: // attributeType is not derived from System.Attribute. // // T:System.Reflection.AmbiguousMatchException: // More than one of the requested attributes was found. public static Attribute GetCustomAttribute(Module element, Type attributeType, bool inherit); // // 摘要: // Retrieves a custom attribute applied to a method parameter. Parameters specify // the method parameter, the type of the custom attribute to search for, and whether // to search ancestors of the method parameter. // // 参数: // element: // An object derived from the System.Reflection.ParameterInfo class that describes // a parameter of a member of a class. // // attributeType: // The type, or a base type, of the custom attribute to search for. // // inherit: // If true, specifies to also search the ancestors of element for custom attributes. // // 返回结果: // A reference to the single custom attribute of type attributeType that is applied // to element, or null if there is no such attribute. // // 异常: // T:System.ArgumentNullException: // element or attributeType is null. // // T:System.ArgumentException: // attributeType is not derived from System.Attribute. // // T:System.Reflection.AmbiguousMatchException: // More than one of the requested attributes was found. // // T:System.TypeLoadException: // A custom attribute type cannot be loaded. public static Attribute GetCustomAttribute(ParameterInfo element, Type attributeType, bool inherit); // // 摘要: // Retrieves an array of the custom attributes applied to a member of a type. A // parameter specifies the member. // // 参数: // element: // An object derived from the System.Reflection.MemberInfo class that describes // a constructor, event, field, method, or property member of a class. // // 返回结果: // An System.Attribute array that contains the custom attributes applied to element, // or an empty array if no such custom attributes exist. // // 异常: // T:System.ArgumentNullException: // element is null. // // T:System.NotSupportedException: // element is not a constructor, method, property, event, type, or field. // // T:System.TypeLoadException: // A custom attribute type cannot be loaded. public static Attribute[] GetCustomAttributes(MemberInfo element); // // 摘要: // Retrieves an array of the custom attributes applied to a method parameter. A // parameter specifies the method parameter. // // 参数: // element: // An object derived from the System.Reflection.ParameterInfo class that describes // a parameter of a member of a class. // // 返回结果: // An System.Attribute array that contains the custom attributes applied to element, // or an empty array if no such custom attributes exist. // // 异常: // T:System.ArgumentNullException: // element is null. // // T:System.TypeLoadException: // A custom attribute type cannot be loaded. public static Attribute[] GetCustomAttributes(ParameterInfo element); // // 摘要: // Retrieves an array of the custom attributes applied to an assembly. A parameter // specifies the assembly. // // 参数: // element: // An object derived from the System.Reflection.Assembly class that describes a // reusable collection of modules. // // 返回结果: // An System.Attribute array that contains the custom attributes applied to element, // or an empty array if no such custom attributes exist. // // 异常: // T:System.ArgumentNullException: // element is null. public static Attribute[] GetCustomAttributes(Assembly element); // // 摘要: // Retrieves an array of the custom attributes applied to a module. A parameter // specifies the module. // // 参数: // element: // An object derived from the System.Reflection.Module class that describes a portable // executable file. // // 返回结果: // An System.Attribute array that contains the custom attributes applied to element, // or an empty array if no such custom attributes exist. // // 异常: // T:System.ArgumentNullException: // element is null. public static Attribute[] GetCustomAttributes(Module element); // // 摘要: // Retrieves an array of the custom attributes applied to an assembly. Parameters // specify the assembly, and an ignored search option. // // 参数: // element: // An object derived from the System.Reflection.Assembly class that describes a // reusable collection of modules. // // inherit: // This parameter is ignored, and does not affect the operation of this method. // // 返回结果: // An System.Attribute array that contains the custom attributes applied to element, // or an empty array if no such custom attributes exist. // // 异常: // T:System.ArgumentNullException: // element or attributeType is null. public static Attribute[] GetCustomAttributes(Assembly element, bool inherit); // // 摘要: // Retrieves an array of the custom attributes applied to an assembly. Parameters // specify the assembly, and the type of the custom attribute to search for. // // 参数: // element: // An object derived from the System.Reflection.Assembly class that describes a // reusable collection of modules. // // attributeType: // The type, or a base type, of the custom attribute to search for. // // 返回结果: // An System.Attribute array that contains the custom attributes of type attributeType // applied to element, or an empty array if no such custom attributes exist. // // 异常: // T:System.ArgumentNullException: // element or attributeType is null. // // T:System.ArgumentException: // attributeType is not derived from System.Attribute. public static Attribute[] GetCustomAttributes(Assembly element, Type attributeType); // // 摘要: // Retrieves an array of the custom attributes applied to a module. Parameters specify // the module, and an ignored search option. // // 参数: // element: // An object derived from the System.Reflection.Module class that describes a portable // executable file. // // inherit: // This parameter is ignored, and does not affect the operation of this method. // // 返回结果: // An System.Attribute array that contains the custom attributes applied to element, // or an empty array if no such custom attributes exist. // // 异常: // T:System.ArgumentNullException: // element or attributeType is null. public static Attribute[] GetCustomAttributes(Module element, bool inherit); // // 摘要: // Retrieves an array of the custom attributes applied to a member of a type. Parameters // specify the member, and the type of the custom attribute to search for. // // 参数: // element: // An object derived from the System.Reflection.MemberInfo class that describes // a constructor, event, field, method, or property member of a class. // // type: // The type, or a base type, of the custom attribute to search for. // // 返回结果: // An System.Attribute array that contains the custom attributes of type type applied // to element, or an empty array if no such custom attributes exist. // // 异常: // T:System.ArgumentNullException: // element or type is null. // // T:System.ArgumentException: // type is not derived from System.Attribute. // // T:System.NotSupportedException: // element is not a constructor, method, property, event, type, or field. // // T:System.TypeLoadException: // A custom attribute type cannot be loaded. public static Attribute[] GetCustomAttributes(MemberInfo element, Type type); // // 摘要: // Retrieves an array of the custom attributes applied to a member of a type. Parameters // specify the member, the type of the custom attribute to search for, and whether // to search ancestors of the member. // // 参数: // element: // An object derived from the System.Reflection.MemberInfo class that describes // a constructor, event, field, method, or property member of a class. // // inherit: // If true, specifies to also search the ancestors of element for custom attributes. // // 返回结果: // An System.Attribute array that contains the custom attributes applied to element, // or an empty array if no such custom attributes exist. // // 异常: // T:System.ArgumentNullException: // element is null. // // T:System.NotSupportedException: // element is not a constructor, method, property, event, type, or field. // // T:System.TypeLoadException: // A custom attribute type cannot be loaded. public static Attribute[] GetCustomAttributes(MemberInfo element, bool inherit); // // 摘要: // Retrieves an array of the custom attributes applied to a method parameter. Parameters // specify the method parameter, and whether to search ancestors of the method parameter. // // 参数: // element: // An object derived from the System.Reflection.ParameterInfo class that describes // a parameter of a member of a class. // // inherit: // If true, specifies to also search the ancestors of element for custom attributes. // // 返回结果: // An System.Attribute array that contains the custom attributes applied to element, // or an empty array if no such custom attributes exist. // // 异常: // T:System.ArgumentException: // The System.Reflection.ParameterInfo.Member property of element is null. // // T:System.ArgumentNullException: // element is null. // // T:System.TypeLoadException: // A custom attribute type cannot be loaded. public static Attribute[] GetCustomAttributes(ParameterInfo element, bool inherit); // // 摘要: // Retrieves an array of the custom attributes applied to a method parameter. Parameters // specify the method parameter, and the type of the custom attribute to search // for. // // 参数: // element: // An object derived from the System.Reflection.ParameterInfo class that describes // a parameter of a member of a class. // // attributeType: // The type, or a base type, of the custom attribute to search for. // // 返回结果: // An System.Attribute array that contains the custom attributes of type attributeType // applied to element, or an empty array if no such custom attributes exist. // // 异常: // T:System.ArgumentNullException: // element or attributeType is null. // // T:System.ArgumentException: // attributeType is not derived from System.Attribute. // // T:System.TypeLoadException: // A custom attribute type cannot be loaded. public static Attribute[] GetCustomAttributes(ParameterInfo element, Type attributeType); // // 摘要: // Retrieves an array of the custom attributes applied to a module. Parameters specify // the module, and the type of the custom attribute to search for. // // 参数: // element: // An object derived from the System.Reflection.Module class that describes a portable // executable file. // // attributeType: // The type, or a base type, of the custom attribute to search for. // // 返回结果: // An System.Attribute array that contains the custom attributes of type attributeType // applied to element, or an empty array if no such custom attributes exist. // // 异常: // T:System.ArgumentNullException: // element or attributeType is null. // // T:System.ArgumentException: // attributeType is not derived from System.Attribute. public static Attribute[] GetCustomAttributes(Module element, Type attributeType); // // 摘要: // Retrieves an array of the custom attributes applied to a member of a type. Parameters // specify the member, the type of the custom attribute to search for, and whether // to search ancestors of the member. // // 参数: // element: // An object derived from the System.Reflection.MemberInfo class that describes // a constructor, event, field, method, or property member of a class. // // type: // The type, or a base type, of the custom attribute to search for. // // inherit: // If true, specifies to also search the ancestors of element for custom attributes. // // 返回结果: // An System.Attribute array that contains the custom attributes of type type applied // to element, or an empty array if no such custom attributes exist. // // 异常: // T:System.ArgumentNullException: // element or type is null. // // T:System.ArgumentException: // type is not derived from System.Attribute. // // T:System.NotSupportedException: // element is not a constructor, method, property, event, type, or field. // // T:System.TypeLoadException: // A custom attribute type cannot be loaded. public static Attribute[] GetCustomAttributes(MemberInfo element, Type type, bool inherit); // // 摘要: // Retrieves an array of the custom attributes applied to a module. Parameters specify // the module, the type of the custom attribute to search for, and an ignored search // option. // // 参数: // element: // An object derived from the System.Reflection.Module class that describes a portable // executable file. // // attributeType: // The type, or a base type, of the custom attribute to search for. // // inherit: // This parameter is ignored, and does not affect the operation of this method. // // 返回结果: // An System.Attribute array that contains the custom attributes of type attributeType // applied to element, or an empty array if no such custom attributes exist. // // 异常: // T:System.ArgumentNullException: // element or attributeType is null. // // T:System.ArgumentException: // attributeType is not derived from System.Attribute. public static Attribute[] GetCustomAttributes(Module element, Type attributeType, bool inherit); // // 摘要: // Retrieves an array of the custom attributes applied to a method parameter. Parameters // specify the method parameter, the type of the custom attribute to search for, // and whether to search ancestors of the method parameter. // // 参数: // element: // An object derived from the System.Reflection.ParameterInfo class that describes // a parameter of a member of a class. // // attributeType: // The type, or a base type, of the custom attribute to search for. // // inherit: // If true, specifies to also search the ancestors of element for custom attributes. // // 返回结果: // An System.Attribute array that contains the custom attributes of type attributeType // applied to element, or an empty array if no such custom attributes exist. // // 异常: // T:System.ArgumentNullException: // element or attributeType is null. // // T:System.ArgumentException: // attributeType is not derived from System.Attribute. // // T:System.TypeLoadException: // A custom attribute type cannot be loaded. public static Attribute[] GetCustomAttributes(ParameterInfo element, Type attributeType, bool inherit); // // 摘要: // Retrieves an array of the custom attributes applied to an assembly. Parameters // specify the assembly, the type of the custom attribute to search for, and an // ignored search option. // // 参数: // element: // An object derived from the System.Reflection.Assembly class that describes a // reusable collection of modules. // // attributeType: // The type, or a base type, of the custom attribute to search for. // // inherit: // This parameter is ignored, and does not affect the operation of this method. // // 返回结果: // An System.Attribute array that contains the custom attributes of type attributeType // applied to element, or an empty array if no such custom attributes exist. // // 异常: // T:System.ArgumentNullException: // element or attributeType is null. // // T:System.ArgumentException: // attributeType is not derived from System.Attribute. public static Attribute[] GetCustomAttributes(Assembly element, Type attributeType, bool inherit); // // 摘要: // Determines whether any custom attributes of a specified type are applied to a // module. Parameters specify the module, and the type of the custom attribute to // search for. // // 参数: // element: // An object derived from the System.Reflection.Module class that describes a portable // executable file. // // attributeType: // The type, or a base type, of the custom attribute to search for. // // 返回结果: // true if a custom attribute of type attributeType is applied to element; otherwise, // false. // // 异常: // T:System.ArgumentNullException: // element or attributeType is null. // // T:System.ArgumentException: // attributeType is not derived from System.Attribute. public static bool IsDefined(Module element, Type attributeType); // // 摘要: // Determines whether any custom attributes are applied to a method parameter. Parameters // specify the method parameter, and the type of the custom attribute to search // for. // // 参数: // element: // An object derived from the System.Reflection.ParameterInfo class that describes // a parameter of a member of a class. // // attributeType: // The type, or a base type, of the custom attribute to search for. // // 返回结果: // true if a custom attribute of type attributeType is applied to element; otherwise, // false. // // 异常: // T:System.ArgumentNullException: // element or attributeType is null. // // T:System.ArgumentException: // attributeType is not derived from System.Attribute. public static bool IsDefined(ParameterInfo element, Type attributeType); // // 摘要: // Determines whether any custom attributes are applied to an assembly. Parameters // specify the assembly, and the type of the custom attribute to search for. // // 参数: // element: // An object derived from the System.Reflection.Assembly class that describes a // reusable collection of modules. // // attributeType: // The type, or a base type, of the custom attribute to search for. // // 返回结果: // true if a custom attribute of type attributeType is applied to element; otherwise, // false. // // 异常: // T:System.ArgumentNullException: // element or attributeType is null. // // T:System.ArgumentException: // attributeType is not derived from System.Attribute. public static bool IsDefined(Assembly element, Type attributeType); // // 摘要: // Determines whether any custom attributes are applied to a member of a type. Parameters // specify the member, and the type of the custom attribute to search for. // // 参数: // element: // An object derived from the System.Reflection.MemberInfo class that describes // a constructor, event, field, method, type, or property member of a class. // // attributeType: // The type, or a base type, of the custom attribute to search for. // // 返回结果: // true if a custom attribute of type attributeType is applied to element; otherwise, // false. // // 异常: // T:System.ArgumentNullException: // element or attributeType is null. // // T:System.ArgumentException: // attributeType is not derived from System.Attribute. // // T:System.NotSupportedException: // element is not a constructor, method, property, event, type, or field. public static bool IsDefined(MemberInfo element, Type attributeType); // // 摘要: // Determines whether any custom attributes are applied to a member of a type. Parameters // specify the member, the type of the custom attribute to search for, and whether // to search ancestors of the member. // // 参数: // element: // An object derived from the System.Reflection.MemberInfo class that describes // a constructor, event, field, method, type, or property member of a class. // // attributeType: // The type, or a base type, of the custom attribute to search for. // // inherit: // If true, specifies to also search the ancestors of element for custom attributes. // // 返回结果: // true if a custom attribute of type attributeType is applied to element; otherwise, // false. // // 异常: // T:System.ArgumentNullException: // element or attributeType is null. // // T:System.ArgumentException: // attributeType is not derived from System.Attribute. // // T:System.NotSupportedException: // element is not a constructor, method, property, event, type, or field. public static bool IsDefined(MemberInfo element, Type attributeType, bool inherit); // // 摘要: // Determines whether any custom attributes are applied to a module. Parameters // specify the module, the type of the custom attribute to search for, and an ignored // search option. // // 参数: // element: // An object derived from the System.Reflection.Module class that describes a portable // executable file. // // attributeType: // The type, or a base type, of the custom attribute to search for. // // inherit: // This parameter is ignored, and does not affect the operation of this method. // // 返回结果: // true if a custom attribute of type attributeType is applied to element; otherwise, // false. // // 异常: // T:System.ArgumentNullException: // element or attributeType is null. // // T:System.ArgumentException: // attributeType is not derived from System.Attribute. public static bool IsDefined(Module element, Type attributeType, bool inherit); // // 摘要: // Determines whether any custom attributes are applied to an assembly. Parameters // specify the assembly, the type of the custom attribute to search for, and an // ignored search option. // // 参数: // element: // An object derived from the System.Reflection.Assembly class that describes a // reusable collection of modules. // // attributeType: // The type, or a base type, of the custom attribute to search for. // // inherit: // This parameter is ignored, and does not affect the operation of this method. // // 返回结果: // true if a custom attribute of type attributeType is applied to element; otherwise, // false. // // 异常: // T:System.ArgumentNullException: // element or attributeType is null. // // T:System.ArgumentException: // attributeType is not derived from System.Attribute. public static bool IsDefined(Assembly element, Type attributeType, bool inherit); // // 摘要: // Determines whether any custom attributes are applied to a method parameter. Parameters // specify the method parameter, the type of the custom attribute to search for, // and whether to search ancestors of the method parameter. // // 参数: // element: // An object derived from the System.Reflection.ParameterInfo class that describes // a parameter of a member of a class. // // attributeType: // The type, or a base type, of the custom attribute to search for. // // inherit: // If true, specifies to also search the ancestors of element for custom attributes. // // 返回结果: // true if a custom attribute of type attributeType is applied to element; otherwise, // false. // // 异常: // T:System.ArgumentNullException: // element or attributeType is null. // // T:System.ArgumentException: // attributeType is not derived from System.Attribute. // // T:System.ExecutionEngineException: // element is not a method, constructor, or type. public static bool IsDefined(ParameterInfo element, Type attributeType, bool inherit); // // 摘要: // Returns a value that indicates whether this instance is equal to a specified // object. // // 参数: // obj: // An System.Object to compare with this instance or null. // // 返回结果: // true if obj equals the type and value of this instance; otherwise, false. [SecuritySafeCriticalAttribute] public override bool Equals(object obj); // // 摘要: // Returns the hash code for this instance. // // 返回结果: // A 32-bit signed integer hash code. [SecuritySafeCriticalAttribute] public override int GetHashCode(); // // 摘要: // When overridden in a derived class, indicates whether the value of this instance // is the default value for the derived class. // // 返回结果: // true if this instance is the default attribute for the class; otherwise, false. public virtual bool IsDefaultAttribute(); // // 摘要: // When overridden in a derived class, returns a value that indicates whether this // instance equals a specified object. // // 参数: // obj: // An System.Object to compare with this instance of System.Attribute. // // 返回结果: // true if this instance equals obj; otherwise, false. public virtual bool Match(object obj); } }
通过定义我们可以看到特性的本质其实是一个类,所有的特性都直接或间接继承Attribute。
一般特性以“Attribute”结尾,在书写时可以省略Attribute,如果不是以Attribute结尾则不能省略。
二、特性与注释
注释:增加注释后,在Visual Studio中可以看到方法的注释说明,但在程序中无法获取。
特性:AttributeUsageAttribute、ObsoleteAttribute等可以影响编译器,SerializableAttribute、HttpPostAttribute、HttpGetAttribute、HttpGetAttribute、FromBodyAttribute等可以影响程序运行。
三、特性的使用
一)几个特殊特性
1、ObsoleteAttribute 如图在UserModel上标记ObsoleteAttribute特性并指定error为true时,可以强制编译器报错
#region 程序集 mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089 // C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.5.2\mscorlib.dll #endregion using System.Runtime.InteropServices; namespace System { // // 摘要: // 标记不再使用的程序元素。此类不能被继承。 [AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Enum | AttributeTargets.Constructor | AttributeTargets.Method | AttributeTargets.Property | AttributeTargets.Field | AttributeTargets.Event | AttributeTargets.Interface | AttributeTargets.Delegate, Inherited = false)] [ComVisible(true)] public sealed class ObsoleteAttribute : Attribute { // // 摘要: // 使用默认属性初始化 System.ObsoleteAttribute 类的新实例。 public ObsoleteAttribute(); // // 摘要: // 使用指定的变通方法消息初始化 System.ObsoleteAttribute 类的新实例。 // // 参数: // message: // 描述可选的变通方法的文本字符串。 public ObsoleteAttribute(string message); // // 摘要: // 使用变通方法消息和布尔值初始化 System.ObsoleteAttribute 类的新实例,该布尔值指示是否将使用已过时的元素视为错误。 // // 参数: // message: // 描述可选的变通方法的文本字符串。 // // error: // 指示是否将使用已过时的元素视为错误的布尔值。 public ObsoleteAttribute(string message, bool error); // // 摘要: // 获取指示编译器是否将使用已过时的程序元素视为错误的布尔值。 // // 返回结果: // 如果将使用已过时的元素视为错误,则为 true;否则为 false。默认值为 false。 public bool IsError { get; } // // 摘要: // 获取变通方法消息,包括对可选程序元素的说明。 // // 返回结果: // 变通方法文本字符串。 public string Message { get; } } }
2、AttributeUsageAttribute 修饰特性的特性 ValidOn指定特性可以使用的范围 默认值为 All,AllowMultiple标记特性是否可以重复修饰 默认值为 false,Inherited标记特性是否可以被继承 默认值为 true
#region 程序集 mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089 // C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.5.2\mscorlib.dll #endregion using System.Runtime.InteropServices; namespace System { // // 摘要: // 指定另一特性类的用法。此类不能被继承。 [AttributeUsage(AttributeTargets.Class, Inherited = true)] [ComVisible(true)] public sealed class AttributeUsageAttribute : Attribute { // // 摘要: // 用指定的 System.AttributeTargets、System.AttributeUsageAttribute.AllowMultiple 值和 // System.AttributeUsageAttribute.Inherited 值列表初始化 System.AttributeUsageAttribute // 类的新实例。 // // 参数: // validOn: // 使用按位"或"运算符组合的一组值,用于指示哪些程序元素是有效的。 public AttributeUsageAttribute(AttributeTargets validOn); // // 摘要: // 获取或设置一个布尔值,该值指示能否为一个程序元素指定多个指示属性实例。 // // 返回结果: // 如果允许指定多个实例,则为 true;否则为 false。默认值为 false。 public bool AllowMultiple { get; set; } // // 摘要: // 获取或设置一个布尔值,该值指示指示的属性能否由派生类和重写成员继承。 // // 返回结果: // 如果该属性可由派生类和重写成员继承,则为 true,否则为 false。默认值为 true。 public bool Inherited { get; set; } // // 摘要: // 获取一组值,这组值标识指示的属性可应用到的程序元素。 // // 返回结果: // 一个或多个 System.AttributeTargets 值。默认值为 All。 public AttributeTargets ValidOn { get; } } }
二)使用范围
[AttributeUsage(AttributeTargets.All,AllowMultiple =true,Inherited =true)] public class CustomAttribute:Attribute { public CustomAttribute() { } public CustomAttribute(int Id) { this._id = Id; } public int _id; public string Name { get; set; } public int Show() { return this._id; } }
[Custom]//修饰类 public class AttributeTest { [Custom]//修饰字段 public string field; [Custom]//修饰属性 public string Property { get; set; } [return: Custom]//修饰返回值 可以被堆叠修饰,也可以用‘,’隔开修饰 [Custom,Custom(1)]//修饰方法,可以被同一特性重复修饰 public string DoNothing([Custom]string test)//修饰方法参数 { return test; } [Custom]//修饰接口 public interface ITestInterFace { } [Custom]//修饰委托 public delegate void TestDelegate(); [Custom]//修饰事件 public event TestDelegate TestHandle; }
三)特性的使用
特性单独使用,视乎并没有作用,在方法、属性、字段上标记特性,对程序并没有影响,如果把反射结合起来,特性就会产生巨大的价值。
public class DisplayNameAttribute:Attribute { public DisplayNameAttribute(string displayName) { this.DisplayName = displayName; } public string DisplayName; }
[DisplayName("用户状态")] public enum UserState { /// <summary> /// 正常 /// </summary> [DisplayName("正常")] Normal = 0, /// <summary> /// 冻结 /// </summary> [DisplayName("冻结")] Frozen = 1, /// <summary> /// 删除 /// </summary> [DisplayName("删除")] Deleted = 2 }
public class TableNameAttribute:Attribute { public TableNameAttribute(string tableName) { this.TableName = tableName; } public string TableName; }
[Serializable] [TableName("User")] public class UserModel : BaseModel { /// <summary> /// Name /// </summary> [DisplayName("姓名")] public string Name { get; set; } /// <summary> /// Account /// </summary> [DisplayName("账户")] [Required] public string Account { get; set; } /// <summary> /// Password /// </summary> [DisplayName("密码")] [Required] [StringLength(6,16)] public string Password { get; set; } /// <summary> /// Email /// </summary> [DisplayName("邮箱")] [Email] public string Email { get; set; } /// <summary> /// Mobile /// </summary> [DisplayName("手机号")] [Mobile] public string Mobile { get; set; } /// <summary> /// CompanyId /// </summary> [DisplayName("公司编号")] public int? CompanyId { get; set; } /// <summary> /// CompanyName /// </summary> [DisplayName("公司名称")] public string CompanyName { get; set; } /// <summary> /// 用户状态 0正常 1冻结 2删除 /// </summary> [DisplayName("用户状态")] [TableName("State")] [Required] public int Status { get; set; } /// <summary> /// 用户类型 1 普通用户 2管理员 4超级管理员 /// </summary> [DisplayName("用户类型")] [Required] public int UserType { get; set; } /// <summary> /// LastLoginTime /// </summary> [DisplayName("最近登录时间")] public DateTime? LastLoginTime { get; set; } /// <summary> /// CreateTime /// </summary> [DisplayName("创建时间")] [Required] public DateTime CreateTime { get; set; } /// <summary> /// CreatorId /// </summary> [DisplayName("关联模式")] [Required] public int CreatorId { get; set; } /// <summary> /// LastModifierId /// </summary> [DisplayName("最后修改编号")] public int? LastModifierId { get; set; } /// <summary> /// LastModifyTime /// </summary> [DisplayName("最后修改时间")] public DateTime? LastModifyTime { get; set; } }
using System; using System.Collections.Generic; using System.ComponentModel; using System.Linq; using System.Reflection; /// <summary> /// 反射帮助类 /// </summary> public static class ReflectionHelper { /// <summary> /// 获取成员描述信息 /// </summary> /// <param name="memberInfo">成员</param> /// <returns>描述信息</returns> public static string GetDescription(this MemberInfo memberInfo) { return memberInfo.GetDescription<DescriptionAttribute>(attribute => attribute.Description); } /// <summary> /// 获取成员描述信息 /// </summary> /// <typeparam name="T">特性类型</typeparam> /// <param name="memberInfo">成员</param> /// <param name="func">特性获取描述的委托</param> /// <returns>描述信息</returns> public static string GetDescription<T>(this MemberInfo memberInfo, Func<T, string> func) where T : Attribute { if (memberInfo.IsDefined(typeof(T), true)) { object[] attributes = memberInfo.GetCustomAttributes(typeof(T), true); foreach (T attribute in attributes) { return func(attribute); } } return memberInfo.Name; } }
/// <summary> /// 枚举描述信息帮助类 /// </summary> /// <typeparam name="T"></typeparam> public static class EnumHelper { private static Dictionary<System.Enum, string> dict = new Dictionary<System.Enum, string>(); /// <summary> /// 枚举描述信息 /// </summary> /// <param name="t"></param> /// <returns></returns> public static string GetDescription(this System.Enum t) { if (!dict.Keys.Contains(t)) { Type type = t.GetType(); string name = System.Enum.GetName(type, t); dict.Add(t, type.GetField(name).GetDescription()); } return dict[t]; } /// <summary> /// 枚举描述信息 /// </summary> /// <param name="t"></param> /// <returns></returns> public static string GetDescription<T>(this System.Enum t,Func<T,string> func)where T:Attribute { Type type = t.GetType(); string name = System.Enum.GetName(type, t); return ReflectionHelper.GetDescription<T>(type.GetField(name), func); } }
typeof(UserModel).GetDescription<TableNameAttribute>(attribute => attribute.TableName);//获取UserModel类表名称 typeof(UserState).GetDescription<DisplayNameAttribute>(attribute => attribute.DisplayName);//获取UserState枚举类型的描述信息 UserState.Normal.GetDescription<DisplayNameAttribute>(attribute=>attribute.DisplayName);//获取枚举的描述信息
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原文地址:https://www.cnblogs.com/Dewumu/p/10544887.html