C# 反射

• 

  反射

  Reflection对象用于在运行时获取类型信息。可以访问正在运行的程序的元数据的类位于 System.Reflection 命名空间中。System.Reflection 命名空间包含类，使您获得有关应用程序的信息和动态添加类型，值和对象的应用程序。
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  反射的应用

  反射具有以下应用程序-

  • 它允许在运行时查看属性信息。
  • 它允许检查装配中的各种类型并实例化这些类型。
  • 它允许后期绑定到方法和属性
  • 它允许在运行时创建新类型，然后使用这些类型执行一些任务。
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  查看元数据

  在上一章中，我们提到使用反射可以查看属性信息。

  需要初始化System.Reflection类的MemberInfo对象，以发现与类关联的属性。为此，您将目标类的对象定义为-

  
  System.Reflection.MemberInfo info = typeof(MyClass);
  

  以下程序演示了这一点-

  
  using System;
  
  [AttributeUsage(AttributeTargets.All)]
  public class HelpAttribute : System.Attribute {
     public readonly string Url;
     
     public string Topic   // Topic is a named parameter {
        get {
           return topic;
        }
        set {
           topic = value;
        }
     }
     public HelpAttribute(string url)   // url is a positional parameter {
        this.Url = url;
     }
     private string topic;
  }
  
  [HelpAttribute("Information on the class MyClass")]
  class MyClass {
  
  }
  
  namespace AttributeAppl {
     class Program {
        static void Main(string[] args) {
           System.Reflection.MemberInfo info = typeof(MyClass);
           object[] attributes = info.GetCustomAttributes(true);
           
           for (int i = 0; i < attributes.Length; i++) {
              System.Console.WriteLine(attributes[i]);
           }
           Console.ReadKey();
        }
     }
  }
  

  尝试一下

  编译并运行它时，它将显示附加到类MyClass的自定义属性的名称-

  
  HelpAttribute
  

• 

  例子

  在此示例中，我们使用上一章中创建的DeBugInfo属性，并使用反射来读取Rectangle类中的元数据。

  
  using System;
  using System.Reflection;
  
  namespace BugFixApplication {
     //a custom attribute BugFix to be assigned to a class and its members
     [AttributeUsage(
        AttributeTargets.Class |
        AttributeTargets.Constructor |
        AttributeTargets.Field |
        AttributeTargets.Method |
        AttributeTargets.Property,
        AllowMultiple = true)]
  
     public class DeBugInfo : System.Attribute {
        private int bugNo;
        private string developer;
        private string lastReview;
        public string message;
        
        public DeBugInfo(int bg, string dev, string d) {
           this.bugNo = bg;
           this.developer = dev;
           this.lastReview = d;
        }
        public int BugNo {
           get {
              return bugNo;
           }
        }
        public string Developer {
           get {
              return developer;
           }
        }
        public string LastReview {
           get {
              return lastReview;
           }
        }
        public string Message {
           get {
              return message;
           }
           set {
              message = value;
           }
        }
     }
     [DeBugInfo(45, "Zara Ali", "12/8/2012", Message = "Return type mismatch")]
     [DeBugInfo(49, "Nuha Ali", "10/10/2012", Message = "Unused variable")]
     
     class Rectangle {
        //member variables
        protected double length;
        protected double width;
        
        public Rectangle(double l, double w) {
           length = l;
           width = w;
        }
        [DeBugInfo(55, "Zara Ali", "19/10/2012", Message = "Return type mismatch")]
        public double GetArea() {
           return length * width;
        }
        [DeBugInfo(56, "Zara Ali", "19/10/2012")]
        public void Display() {
           Console.WriteLine("Length: {0}", length);
           Console.WriteLine("Width: {0}", width);
           Console.WriteLine("Area: {0}", GetArea());
        }
     }//end class Rectangle
     
     class ExecuteRectangle {
        static void Main(string[] args) {
           Rectangle r = new Rectangle(4.5, 7.5);
           r.Display();
           Type type = typeof(Rectangle);
           
           //iterating through the attribtues of the Rectangle class
           foreach (Object attributes in type.GetCustomAttributes(false)) {
              DeBugInfo dbi = (DeBugInfo)attributes;
              
              if (null != dbi) {
                 Console.WriteLine("Bug no: {0}", dbi.BugNo);
                 Console.WriteLine("Developer: {0}", dbi.Developer);
                 Console.WriteLine("Last Reviewed: {0}", dbi.LastReview);
                 Console.WriteLine("Remarks: {0}", dbi.Message);
              }
           }
           
           //iterating through the method attribtues
           foreach (MethodInfo m in type.GetMethods()) {
              
              foreach (Attribute a in m.GetCustomAttributes(true)) {
                 DeBugInfo dbi = (DeBugInfo)a;
                 
                 if (null != dbi) {
                    Console.WriteLine("Bug no: {0}, for Method: {1}", dbi.BugNo, m.Name);
                    Console.WriteLine("Developer: {0}", dbi.Developer);
                    Console.WriteLine("Last Reviewed: {0}", dbi.LastReview);
                    Console.WriteLine("Remarks: {0}", dbi.Message);
                 }
              }
           }
           Console.ReadLine();
        }
     }
  }
  

  尝试一下

  编译并执行上述代码后，将产生以下结果-

  
  Length: 4.5
  Width: 7.5
  Area: 33.75
  Bug No: 49
  Developer: Nuha Ali
  Last Reviewed: 10/10/2012
  Remarks: Unused variable
  Bug No: 45
  Developer: Zara Ali
  Last Reviewed: 12/8/2012
  Remarks: Return type mismatch
  Bug No: 55, for Method: GetArea
  Developer: Zara Ali
  Last Reviewed: 19/10/2012
  Remarks: Return type mismatch
  Bug No: 56, for Method: Display
  Developer: Zara Ali
  Last Reviewed: 19/10/2012
  Remarks: