反射对象在运行时获取类型信息的应用
反射对象用于在运行时获取类型信息。提供对正在运行程序的元数据访问的类位于 System.Reflection 命名空间中。
System.Reflection 命名空间包含了可以让你获取应用程序信息并动态地向应用程序添加类型、值和对象的类。
反射的应用
反射有以下应用：
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它允许在运行时创建新类型，并然后使用这些类型执行某些任务。
查看元数据
我们在前一章提到过，使用反射你可以查看属性信息。
为了发现与类相关的属性，需要初始化 System.Reflection 类的 MemberInfo 对象。为此，你定义目标类的对象，如下所示：
System.Reflection.MemberInfo info = typeof(MyClass);
下面的程序演示了这一点：
using System;
[AttributeUsage(AttributeTargets.All)]
public class HelpAttribute : System.Attribute {
public readonly string Url;
public string Topic
get {
return topic;
}
set {
topic = value;
}
}
public HelpAttribute(string url)
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();
}
}
}
当它被编译和运行时，它显示附加到 MyClass 类的自定义属性名称：
HelpAttribute
示例
在这个例子中，我们使用在前一章中创建的 DeBugInfo 属性，并使用反射在 Rectangle 类中读取元数据。
using System;
using System.Reflection;
namespace BugFixApplication {
[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 {
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());
}
}
class ExecuteRectangle {
static void Main(string[] args) {
Rectangle r = new Rectangle(4.5, 7.5);
r.Display();
Type type = typeof(Rectangle);
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);
}
}
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();
}
}
}
当上述代码被编译和执行时，它产生如下结果：
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: