C＃属性可以访问目标类吗？
我想通过使用reflection从属性类访问类的属性。 可能吗？
例如：
class MyAttribute : Attribute { private void AccessTargetClass() { // Do some operations } } [MyAttribute] class TargetClass { } 不是直接的，但为了使属性做任何事情，你已经必须有一个types/成员的句柄，并调用它的GetCustomAttributes方法，所以你可以简单地从那里传递它：
class MyAttribute : Attribute { public void DoSomethingWithDeclaringType(Type t) { } }
像这样使用它：
Type classType = typeof(MyClass); object[] attribs = classType.GetCustomAttributes(typeof(MyAttribute), true); if(attribs.Length > 0) { ((MyAttribute)attribs[0]).DoSomethingWithDeclaringType(classType); }
有些情况下，您不能依靠调用代码来传递types引用。
下面是我熟练解决这个问题的一个解决scheme。 这是一个枪法，但它确实有效。
using System; using System.Reflection; using System.Collections.Generic; using System.Linq; using System.Diagnostics; namespace Ethica.Reflection { /// <summary> /// Helps in discovery of the target of an Attribute /// </summary> /// <typeparam name="TAttribute">An Attribute derived type</typeparam> /// <remarks> /// The .NET framework does not provide navigation from attributes back to their targets, principally for the reason that /// in typical usage scenarios for attributes, the attribute is discovered by a routine which already has a reference to a /// member type. /// /// There are, however, bona-fide cases where an attribute needs to detect it's target - an example is a localizable sub-class of the /// DescriptionAttribute. In order for the DescriptionAttribute to return a localized string, it requires a resource key and, ideally, /// a type reference as the base-key for the ResourceManager. A DescriptionAttribute could not provide this information without /// a reference to it's target type. /// /// Note to callers: /// /// Your Attribute-derived class must implement Equals and GetHashCode, otherwise a run-time exception will occur, since this class /// creates a dictionary of attributes in order to speed up target lookups. /// </remarks> public static class AttributeTargetHelper<TAttribute> where TAttribute : Attribute { /// <summary> /// Map of attributes and their respective targets /// </summary> private static Dictionary<TAttribute, object> targetMap; /// <summary> /// List of assemblies that should not be rescanned for types. /// </summary> private static List<string> skipAssemblies; /// <summary> /// Adds an attribute and it's target to the dictionary /// </summary> /// <param name="attribute"></param> /// <param name="item"></param> private static void Add(TAttribute attribute, object item) { targetMap.Add(attribute, item); } /// <summary> /// Scans an assembly for all instances of the attribute. /// </summary> /// <param name="assembly"></param> private static void ScanAssembly(Assembly assembly) { const BindingFlags memberInfoBinding = BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Static | BindingFlags.Instance; if (!skipAssemblies.Contains(assembly.FullName)) { skipAssemblies.Add(assembly.FullName); Debug.WriteLine("Loading attribute targets for " + typeof(TAttribute).Name + " from assembly " + assembly.FullName); foreach (TAttribute attr in assembly.GetCustomAttributes(typeof(TAttribute), false)) Add(attr, assembly); foreach (Type type in assembly.GetTypes()) { foreach (TAttribute attr in type.GetCustomAttributes(typeof(TAttribute), false)) Add(attr, type); foreach (MemberInfo member in type.GetMembers(memberInfoBinding)) { foreach (TAttribute attr in member.GetCustomAttributes(typeof(TAttribute), false)) Add(attr, member); if (member.MemberType == MemberTypes.Method) foreach (var parameter in ((MethodInfo)member).GetParameters()) foreach (TAttribute attr in parameter.GetCustomAttributes(typeof(TAttribute), false)) Add(attr, parameter); } } } foreach (var assemblyName in assembly.GetReferencedAssemblies()) { if (!skipAssemblies.Contains(assemblyName.FullName)) ScanAssembly(Assembly.Load(assemblyName)); } } /// <summary> /// Returns the target of an attribute. /// </summary> /// <param name="attribute">The attribute for which a target is sought</param> /// <returns>The target of the attribute - either an Assembly, Type or MemberInfo instance.</returns> public static object GetTarget(TAttribute attribute) { object result; if (!targetMap.TryGetValue(attribute, out result)) { // Since types can be loaded at any time, recheck that all assemblies are included... // Walk up the stack in a last-ditch effort to find instances of the attribute. StackTrace stackTrace = new StackTrace(); // get call stack StackFrame[] stackFrames = stackTrace.GetFrames(); // get method calls (frames) // write call stack method names foreach (StackFrame stackFrame in stackFrames) { Console.WriteLine(stackFrame.GetMethod().Name); // write method name ScanAssembly(stackFrame.GetMethod().GetType().Assembly); } if (!targetMap.TryGetValue(attribute, out result)) throw new InvalidProgramException("Cannot find assembly referencing attribute"); } return result; } /// <summary> /// Static constructor for type. /// </summary> static AttributeTargetHelper() { targetMap = new Dictionary<TAttribute, object>(); // Do not load any assemblies reference by the assembly which declares the attribute, since they cannot possibly use the attribute skipAssemblies = new List<string>(typeof(TAttribute).Assembly.GetReferencedAssemblies().Select(c => c.FullName)); // Skip common system assemblies skipAssemblies.Add("System.Core, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"); skipAssemblies.Add("System.Security, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a"); skipAssemblies.Add("System.Xml, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"); skipAssemblies.Add("System.Data.SqlXml, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"); skipAssemblies.Add("System.Configuration, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a"); skipAssemblies.Add("System.Numerics, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"); // Scan the entire application ScanAssembly(Assembly.GetEntryAssembly()); } } /// <summary> /// Extends attributes so that their targets can be discovered /// </summary> public static class AttributeTargetHelperExtension { /// <summary> /// Gets the target of an attribute /// </summary> /// <typeparam name="TAttribute"></typeparam> /// <param name="attribute">The attribute for which a target is sought</param> /// <returns>The target of the attribute - either an Assembly, Type or MemberInfo instance.</returns> public static object GetTarget<TAttribute>(this TAttribute attribute) where TAttribute : Attribute { return AttributeTargetHelper<TAttribute>.GetTarget(attribute); } } }
属性的主要用途是注释：你声明？ 应该以这种或那种方式对待类/方法/属性，但实际上分析所有这些东西的代码应该在其他地方。 所以你打算在属性里做一些事情就是打破这个模式。 我的build议：考虑另一个解决scheme
