屬性和反射

Metadata is information about the data that is information about the types ,code, assembly and so forth stored along with the program.Attributes are a mechanism for adding metadata,such as compiler instructions and other data about your data,methods and classes, to the program itself.

An attribute is an object that represents data you want to associate with an element in your program .The element to which you attach an attribute is referred as the target of the attribute.

 

1.屬性目標

屬性有作用對象的種類，這稱爲屬性目標。在AttributeTargets中聲明

2.使用屬性

放在方括號裏面，並緊貼作用的元素之前，作用於assembly的除外，要放在文件頭部(using語句之後)。可以並列排放組合，也可以使用逗號分隔。

3.自定義屬性--直接看代碼

namespace ConsoleApplication5 { class Program { static void Main(string[] args) { MyMath myMath = new MyMath(); Console.WriteLine( myMath.DoFunc1(5) ); } } /* * 自定義屬性派生於System.Attribute * 創建的時候指定AttributeUsage，第一個參數說明作用的target，第二個說明是否允許使用多於一個的BugFixAttribute屬性 * 屬性命名慣例是在名字後面跟上Attribute。使用的時候[BugFix]，編譯器會先去找BugFix如果找不到去找BugFixAttribute * 屬性接受兩種類型的參數：Positional和Named。Positional parameters are passed in through the constructor and must be passed * in the order declared in the constructor.Named parameters are implemented as fields or as properties.It`s common to create * read-only properties for the positional parameters */ [AttributeUsage(AttributeTargets.Class,AllowMultiple=true)] public class BugFixAttribute : System.Attribute { private int _bugID; private string _date; private string _programmer; private string _comment; public BugFixAttribute(int bugId, string programmer, string date) { _bugID = bugId; _programmer = programmer; _date = date; } public int BugID { get { return _bugID; } } public string Data { get { return _date; } } public string Programmer { get { return _programmer; } } public string Comment { get { return _comment; } set { _comment = value; } } } [BugFix(121,"xuxu","11/05/28")] [BugFix(122,"bubu","11/05/29",Comment="Oh,wrong,fix a bug")] public class MyMath { public double DoFunc1(double param1) { return param1 + DoFunc2(param1); } public double DoFunc2(double param1) { return param1 / 3; } } }

4.反射

反射主要有4種用途-1.查看元數據  2.進行類型發現  3.對方法和properties的遲綁定  4.運行時創建新類型

4.1查看元數據

Type類是反射類的核心，provided to discover the attribute of a member and provide access to the metadata.Type encapsulate a representation of the type of an object.The Type class the primary way to access metadata.Type encapsulates information about the member of a class(eg. fields,methods,properties,events,etc).

class Program { static void Main(string[] args) { Type type = typeof(MyMath); object[] attributes = type.GetCustomAttributes(typeof(BugFixAttribute),false); foreach (var item in attributes) { BugFixAttribute attribute = (BugFixAttribute)item; Console.WriteLine( "BugId:" + attribute.BugID + " Programmmer:" + attribute.Programmer + " Date:" + attribute.Date + " Comment:"+attribute.Comment); } } } /* * 自定義屬性派生於System.Attribute * 創建的時候指定AttributeUsage，第一個參數說明作用的target，第二個說明是否允許使用多於一個的BugFixAttribute屬性 * 屬性命名慣例是在名字後面跟上Attribute。使用的時候[BugFix]，編譯器會先去找BugFix如果找不到去找 BugFixAttribute * 屬性接受兩種類型的參數：Positional和Named。Positional parameters are passed in through the constructor and must be passed * in the order declared in the constructor.Named parameters are implemented as fields or as properties.It`s common to create * read-only properties for the positional parameters */ [AttributeUsage(AttributeTargets.Class,AllowMultiple=true)] public class BugFixAttribute : System.Attribute { private int _bugID; private string _date; private string _programmer; private string _comment; public BugFixAttribute(int bugId, string programmer, string date) { _bugID = bugId; _programmer = programmer; _date = date; } public int BugID { get { return _bugID; } } public string Date { get { return _date; } } public string Programmer { get { return _programmer; } } public string Comment { get { return _comment; } set { _comment = value; } } } [BugFix(121,"xuxu","11/05/28")] [BugFix(122,"bubu","11/05/29",Comment="Oh,wrong,fix a bug")] public class MyMath { public double DoFunc1(double param1) { return param1 + DoFunc2(param1); } public double DoFunc2(double param1) { return param1 / 3; } }

4.2 類型發現

This allows you to examine the types in an assembly and interact with or instantiate those types. You can use reflection to explore and examine the contents of an assembly.You can find the types associated with a module;the methods,fields,properties,and events associated with a type,as well as the signatures of each of the type`s methods;the interfaces supported by the type;and the type`s base class.

class Program { static void Main(string[] args) { Assembly assem = Assembly.Load("Mscorlib"); Type[] types = assem.GetTypes(); foreach (var item in types) Console.WriteLine("Type is {0}",item); Console.WriteLine("{0} types found",types.Length); } }

查看一個類型的所有成員

class Program { static void Main(string[] args) { Type theType = Type.GetType("System.Reflection.Assembly"); Console.WriteLine(theType); MemberInfo[] infoArray = theType.GetMembers(); foreach (MemberInfo item in infoArray) { Console.WriteLine("{0} is a {1}",item,item.MemberType); } } }

僅查找方法

MemberInfo[] infoArray = theType.GetMethods();

指定查找

MemberInfo[] infoArray = theType.FindMembers(MemberTypes.Method,BindingFlags.Public|BindingFlags.Static,Type.FilterName,"Get*");

4.3 對方法和properties的遲綁定

allows the programmer to invoke properties and methods on objects dynamically instantiated,based on type discovery.This in also known as dynamic invocation.

可能需要使用Activator動態加載一個類的實例，如果對於一個靜態的類則不需要。解釋一下：

1.首先獲得類型，

2.然後獲得方法，傳入函數原型

3.準備好方法的參數

4.調用，注意第一個參數，如果是靜態類型，傳入靜態類型的type，否則要傳入instance的名字。

class Program { static void Main(string[] args) { Type theMathType = Type.GetType( "System.Math" ); Type[] paramTypes = new Type[1]; paramTypes[0] = Type.GetType( "System.Double" ); MethodInfo CosineInfo = theMathType.GetMethod("Cos", paramTypes); object[] parameters = new object[1]; parameters[0] = 45 * (Math.PI / 180); Console.WriteLine( CosineInfo.Invoke(theMathType,parameters) ); } }