Reflection 对象用于在运行时获取类型信息.允许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 命名空间包含允许您获取有关应用程序的信息并动态向应用程序添加类型，值和对象的类.
Reflection具有以下应用程序 :
它允许在运行时查看属性信息.
它允许检查程序集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某些任务.
我们在前一章已经提到使用反射可以查看属性信息.
系统的MemberInfo 对象需要初始化.Reflection 类以发现与类关联的属性.为此，您可以定义目标类的对象，为 :
System.Reflection.MemberInfo info = typeof(MyClass);
以下程序演示了这个 :
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();
}
}
}编译并运行时，它会显示附加到的自定义属性的名称class MyClass :
HelpAttribute
在此示例中，我们使用上一章中创建的 DeBugInfo 属性，并使用反射来读取矩形 class.
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();
}
}
}编译并执行上述代码时，会产生以下结果 :
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:
