C#反射總結(jié)

Reflection，中文翻譯為反射。這是.Net中獲取運(yùn)行時類型信息的方式，.Net的應(yīng)用程序由幾個部分：‘程序集(Assembly)’、‘模塊(Module)’、‘類型(class)’組成，而反射提供一種編程的方式，讓程序員可以在程序運(yùn)行期獲得這幾個組成部分的相關(guān)信息，例如：Assembly類可以獲得正在運(yùn)行的裝配件信息，也可以動態(tài)的加載裝配件，以及在裝配件中查找類型信息，并創(chuàng)建該類型的實例。Type類可以獲得對象的類型信息，此信息包含對象的所有要素：方法、構(gòu)造器、屬性等等，通過Type類可以得到這些要素的信息，并且調(diào)用之。MethodInfo包含方法的信息，通過這個類可以得到方法的名稱、參數(shù)、返回值等，并且可以調(diào)用之。諸如此類，還有FieldInfo、EventInfo等等，這些類都包含在System.Reflection命名空間下。
一、Type類于獲取類型信息
System.Type 類對于反射起著核心的作用。當(dāng)反射請求加載的類型時，公共語言運(yùn)行庫將為它創(chuàng)建一個 Type。您可以使用 Type 對象的方法、字段、屬性和嵌套類來查找有關(guān)該類型的所有信息。
大家運(yùn)行一下下面的代碼根據(jù)結(jié)果分析一下就能比較清楚的理解Type了

?

獲取類型信息
namespace?ConsoleApplication2
{
????class?Program
????{
????????static?void?Main(string[]?args)
????????{
????????????MyClass?m?=?new?MyClass();
????????????Type?type?=?m.GetType();
????????????Console.WriteLine("類型名:"?+?type.Name);
????????????Console.WriteLine("類全名："+type.FullName);
????????????Console.WriteLine("命名空間名:"+type.Namespace);
????????????Console.WriteLine("程序集名："+type.Assembly);
????????????Console.WriteLine("模塊名:"+type.Module);
????????????Console.WriteLine("基類名："+type.BaseType);
????????????Console.WriteLine("是否類："+type.IsClass);
????????????Console.WriteLine("類的公共成員：");
????????????MemberInfo[]?memberInfos?=?type.GetMembers();//得到所有公共成員
????????????foreach?(var?item?in?memberInfos)
????????????{
????????????????Console.WriteLine("{0}:{1}",item.MemberType,item);
????????????}
????????}
????????
????}
????class?MyClass
????{
????????public?string?m;
????????public?void?test()
????????{?}
????????public?int?MyProperty?{?get;?set;?}

????}
}

?

二、獲取程序集元數(shù)據(jù)
Assembly類定義了一個程序集，它是一個可重用、無版本沖突并且可自我描述的公共語言運(yùn)行庫應(yīng)用程序構(gòu)造塊。因為程序集中是使用元數(shù)據(jù)進(jìn)行自我描述的，所以我們就能通過其元數(shù)據(jù)得到程序集內(nèi)部的構(gòu)成。結(jié)合Assembly和反射能夠獲取程序集的元數(shù)據(jù)，但是首先要將程序集裝入內(nèi)存中。可以使用Assembly類的多種靜態(tài)Load方法加載程序集。
下面的程序顯示程序集的信息

?

Code
public?static?void?Main()
????????{
????????????//獲取當(dāng)前執(zhí)行代碼的程序集
????????????Assembly?assem?=?Assembly.GetExecutingAssembly();

????????????Console.WriteLine("程序集全名:"+assem.FullName);
????????????Console.WriteLine("程序集的版本："+assem.GetName().Version);
????????????Console.WriteLine("程序集初始位置:"+assem.CodeBase);
????????????Console.WriteLine("程序集位置："+assem.Location);
????????????Console.WriteLine("程序集入口："+assem.EntryPoint);

????????????Type[]?types?=?assem.GetTypes();
????????????Console.WriteLine("程序集下包含的類型:");
????????????foreach?(var?item?in?types)
????????????{
????????????????Console.WriteLine("類："+item.Name);
????????????}
????????????
????????}

?

三、動態(tài)加載類型
早綁定是在編譯時綁定對象類型，而晚綁定是在運(yùn)行時才綁定對象的類型。利用反射可以實現(xiàn)晚綁定，即動態(tài)加載類型，并調(diào)用他們的方法，下邊是MSDN中的一個例子，詳細(xì)的解釋信息見注釋

?

動態(tài)加載類型
namespace?ConsoleApplication2
{
????public?class?Example
????{
????????private?int?factor;
????????public?Example(int?f)
????????{
????????????factor?=?f;
????????}

????????public?int?SampleMethod(int?x)
????????{
????????????Console.WriteLine("\nExample.SampleMethod({0})?executes.",?x);
????????????return?x?*?factor;
????????}

????????public?static?void?Main()
????????{
????????????//獲取當(dāng)前執(zhí)行代碼的程序集
????????????Assembly?assem?=?Assembly.GetExecutingAssembly();

????????????Console.WriteLine("Assembly?Full?Name:");
????????????Console.WriteLine(assem.FullName);

????????????//?The?AssemblyName?type?can?be?used?to?parse?the?full?name.
????????????AssemblyName?assemName?=?assem.GetName();
????????????Console.WriteLine("\nName:?{0}",?assemName.Name);
????????????Console.WriteLine("Version:?{0}.{1}",
????????????????assemName.Version.Major,?assemName.Version.Minor);
????????????Console.WriteLine("\nAssembly?CodeBase:");
????????????Console.WriteLine(assem.CodeBase);
????????????//?從程序集眾創(chuàng)建一個Example實例并且用object類型的引用o指向它，同時調(diào)用一個輸入?yún)?shù)的構(gòu)造函數(shù)
????????????Object?o?=?assem.CreateInstance("ConsoleApplication2.Example",?false,
????????????????BindingFlags.ExactBinding,
????????????????null,?new?Object[]?{?2?},?null,?null);

????????????//構(gòu)造Example類的一個晚綁定的方法SampleMethod??
????????????MethodInfo?m?=?assem.GetType("ConsoleApplication2.Example").GetMethod("SampleMethod");
????????????//調(diào)用剛才實例化好的Example對象o中的SampleMethod方法，傳入的參數(shù)為42
????????????Object?ret?=?m.Invoke(o,?new?Object[]?{?42?});
????????????Console.WriteLine("SampleMethod?returned?{0}.",?ret);

????????????Console.WriteLine("\nAssembly?entry?point:");
????????????Console.WriteLine(assem.EntryPoint);
????????}
????}

?

反射特性：

[Table(Name="dbo.[User]")]
public partial class User
{
當(dāng)C#編譯器發(fā)現(xiàn)這個屬性有一個特性Table時，首先會把字符串Attribute添加到這個名稱的后面，形成一個組合名稱TableAttribute，然后在其搜索路徑的所有命名空間中搜索有相同類名的類。但要注意，如果該特性名結(jié)尾是Attribute，編譯器就不會把該字符串加到組合名稱中。所有的特性都是從System.Attribute類型上面派生的。
接著我們來看一下Table特性的定制格式
[AttributeUsageAttribute(AttributeTargets.Class, Inherited=true,AllowMultiple=false)]
public class TalbeAttribute:Attribute
{

??? 在定義類型時使用System.AttributeUsage特性來表明這個自定義特性的使用范圍，這里使用了Class樣式，表示TableAttribute特性只能用在其它的Class類型前面，若放置在Interface或Struct類型前面，或者放在對象成員的前面則會出現(xiàn)編譯錯誤。這里還是用語句 AllowMultiple=false 語句來表明對于一個類型，該特性只能用一次，若一個Class類型前面出現(xiàn)多個TableAttribute，則會出現(xiàn)編譯錯誤。若設(shè)置AllowMultiple=true，則該特性可以多次定義，也就是一個Class類型前面可以出現(xiàn)多個相同類型的特性。不過這里我們假設(shè)一個對象只能映射到一個數(shù)據(jù)表上，沒有多重映射，因此就指明對同一個類型該特性不能多次使用。Inherited參數(shù)設(shè)定為true，就表示應(yīng)用到類或接口上的特性也可以自動應(yīng)用到所派生的類或接口上。
我們再看一下定制TalbeAttribute特性的完整例子：

?

?[AttributeUsageAttribute(AttributeTargets.Class,?Inherited?=?false,?AllowMultiple?=?false)]
????public?class?TableAttribute?:?Attribute
????{
????????//保存表名的字段
????????private?string?_tableName;

????????public?TableAttribute()
????????{
????????}

????????public?TableAttribute(string?tableName)
????????{
????????????this._tableName?=?tableName;
????????}

????????///?<summary>
????????///?映射的表名(表的全名:模式名.表名)
????????///?</summary>
????????public?string?TableName
????????{
????????????set
????????????{
????????????????this._tableName?=?value;
????????????}
????????????get
????????????{
????????????????return?this._tableName;
????????????}
????????}
????}

?

?特性也是一個Class類型，可以有多個構(gòu)造函數(shù)，就像C#的new語句一樣，我們向類型附加特性時可以使用不同的初始化參數(shù)來指明使用特性的那個構(gòu)造函數(shù)。我們附加特性時還可以使用“屬性名=屬性值”的方法來直接指明特性的屬性值。該特性中定義了一個TableName屬性，該屬性就是被修飾的對象所映射的數(shù)據(jù)庫表的名稱。

下面我們舉一個使用特性來進(jìn)行O/RMapping的例子，也就是將對象轉(zhuǎn)化成Sql語句

用戶類：

User類

????[Table("User")]
????public?class?User
????{
????????[Colum("userID",?DbType?=?DbType.Int32)]
????????public?int?UserID?{?get;?set;?}
????????[Colum("UserName",?DbType?=?DbType.String)]
????????public?string?UserName?{?get;?set;?}
????}

?

表特性

?

表特性
[AttributeUsageAttribute(AttributeTargets.Class,?Inherited?=?false,?AllowMultiple?=?false)]
????public?class?TableAttribute?:?Attribute
????{
????????//保存表名的字段
????????private?string?_tableName;

????????public?TableAttribute()
????????{
????????}

????????public?TableAttribute(string?tableName)
????????{
????????????this._tableName?=?tableName;
????????}

????????///?<summary>
????????///?映射的表名(表的全名:模式名.表名)
????????///?</summary>
????????public?string?TableName
????????{
????????????set
????????????{
????????????????this._tableName?=?value;
????????????}
????????????get
????????????{
????????????????return?this._tableName;
????????????}
????????}
????}

?

列特性：

?

列特性
?[AttributeUsageAttribute(AttributeTargets.Property,?Inherited?=?false,?AllowMultiple?=?false)]
????public?class?ColumAttribute?:?Attribute
????{
????????private?string?_columName;

????????private?DbType?_dbType?;


????????public?ColumAttribute()
????????{
????????}

????????public?ColumAttribute(string?columName)
????????????:?this()
????????{
????????????this._columName?=?columName;
????????}
?????
????????public?ColumAttribute(string?columName,?DbType?dbType)
????????????:?this(columName)
????????{
????????????this._dbType?=?dbType;
????????}

????????//列名
????????public?virtual?string?ColumName
????????{
????????????set
????????????{
????????????????this._columName?=?value;
????????????}
????????????get
????????????{
????????????????return?this._columName;
????????????}
????????}

????????//描述一些特殊的數(shù)據(jù)庫類型
????????public?DbType?DbType
????????{
????????????get?{?return?_dbType;?}
????????????set?{?_dbType?=?value;?}
????????}

????}

?

?

ORMHelp
?public?class?ORMHelp
????{
????????public?void?Insert(object?table)
????????{
????????????Type?type?=?table.GetType();
????????????//定義一個字典來存放表中字段和值的對應(yīng)序列
????????????Dictionary<string,?string>?columValue?=?new?Dictionary<string,?string>();
????????????StringBuilder?SqlStr=new?StringBuilder();
????????????SqlStr.Append("insert?into?");
????????????//得到表名子
????????????TableAttribute?temp?=?(TalbeAttribute)type.GetCustomAttributes(typeof(TalbeAttribute), false).First();
????????????SqlStr.Append(temp.TableName);
????????????SqlStr.Append("(");
????????????PropertyInfo[]?Propertys=type.GetProperties();
????????????foreach?(var?item?in?Propertys)
????????????{
????????????????object[]?attributes?=?item.GetCustomAttributes(false);
????????????????foreach?(var?item1?in?attributes)
????????????????{
????????????????????//獲得相應(yīng)屬性的值
???????????????????string?value=?table.GetType().InvokeMember(item.Name,?System.Reflection.BindingFlags.GetProperty,?null,?table,?null).ToString();
????????????????????ColumAttribute?colum?=?item1?as?ColumAttribute;
????????????????????if?(colum?!=?null)
????????????????????{
????????????????????????columValue.Add(colum.ColumName,value);
????????????????????}
????????????????}
????????????}
????????????//拼插入操作字符串
????????????foreach?(var?item?in?columValue)
????????????{
????????????????SqlStr.Append(item.Key);
????????????????SqlStr.Append(",");

????????????}
????????????SqlStr.Remove(SqlStr.Length-1,?1);
????????????SqlStr.Append(")?values('");
????????????foreach?(var?item?in?columValue)
????????????{
????????????????SqlStr.Append(item.Value);
????????????????SqlStr.Append("','");


????????????}
????????????SqlStr.Remove(SqlStr.Length?-?2,?2);
????????????SqlStr.Append(")");
????????????Console.WriteLine(SqlStr.ToString());


????????}
????}

SqlStr中的內(nèi)容為insert into User(userID,UserName) values('1','lfm')

前端使用代碼：

?

前端代碼
static?void?Main(string[]?args)
????????{
????????????ORMHelp?o?=?new?ORMHelp();
????????????User?u?=?new?User()?{?UserID=1,UserName="lfm"};
????????????o.Insert(u);
????????}

?

應(yīng)用

?

例子這個東西其實挺難弄得,弄個簡單的,雖然能說明問題但卻容易讓人覺得沒實用價值,弄個有實用價值卻又往往牽扯很多別的技術(shù)甚至牽扯很多業(yè)務(wù)邏輯,看起來很復(fù)雜很難懂。在這里我盡量追求幾個有實用價值又不復(fù)雜的例子。
1、使用反射通過讀取配置文件來動態(tài)的創(chuàng)建相關(guān)類的對象

我們先來看看Main函數(shù)和需要動態(tài)加載的對象在同一個程序集的情況

結(jié)構(gòu)圖：

接口

?

?

接口
interface?ILog
????{
????????bool?Write(string?message);
????????bool?Write(Exception?ex);
????}

?

?

?

?

TextFileLog
class?TextFileLog?:?ILog
????{
????????public?bool?Write(string?message)
????????{
????????????string?fileDir?=?ConfigurationManager.AppSettings["LogTarget"].ToString();
????????????using?(StreamWriter?w?=?File.AppendText(fileDir))
????????????{
????????????????//?w.Write("?Log?Entry?:?");
????????????????w.WriteLine("發(fā)生時間{0}",?DateTime.Now.ToLocalTime().ToString());
????????????????w.WriteLine("日志內(nèi)容為:{0}",?message);
????????????????w.WriteLine("-------------------------------");
????????????????//?Update?the?underlying?file.
????????????????w.Flush();
????????????????w.Close();
????????????}
????????????return?true;
????????}
????????public?bool?Write(Exception?ex)
????????{

????????????Write(ex.Message);
????????????return?true;
????????}
????}

?

?

?

?

XmlFileLog
class?XmlFileLog?:?ILog
????{
????????public?bool?Write(string?message)
????????{
????????????string?xmlFilePath?=?ConfigurationManager.AppSettings["LogTarget"].ToString();
????????????if?(File.Exists(xmlFilePath))
????????????{
????????????????XmlDocument?doc?=?new?XmlDocument();
????????????????doc.Load(xmlFilePath);
????????????????XmlDocumentFragment?docFrag?=?doc.CreateDocumentFragment();
????????????????XmlNode?nod?=?doc.SelectSingleNode("Logs");
????????????????docFrag.InnerXml?=?"<Log><Time>"?+?DateTime.Now.ToLocalTime().ToString()
????????????????????+?"</Time><Message>"?+?message?+?"</Message></Log>";
????????????????nod.AppendChild(docFrag);

????????????????doc.Save(xmlFilePath);
????????????????return?true;
????????????}
????????????else
????????????{
????????????????XmlWriterSettings?settings?=?new?XmlWriterSettings();
????????????????settings.Indent?=?true;?????//設(shè)置縮進(jìn)???????
????????????????settings.ConformanceLevel?=?ConformanceLevel.Auto;
????????????????settings.IndentChars?=?"?";
????????????????settings.OmitXmlDeclaration?=?false;
????????????????using?(XmlWriter?writer?=?XmlWriter.Create(xmlFilePath,?settings))
????????????????{
????????????????????//Start?writing?the?XML?document
????????????????????writer.WriteStartDocument(false);
????????????????????//Start?with?the?root?element
????????????????????writer.WriteStartElement("Logs");
????????????????????writer.WriteStartElement("Log");
????????????????????writer.WriteStartElement("Time");
????????????????????writer.WriteString(DateTime.Now.ToLocalTime().ToString());
????????????????????writer.WriteEndElement();
????????????????????writer.WriteStartElement("Message");
????????????????????writer.WriteString(message);
????????????????????writer.WriteEndElement();
????????????????????writer.WriteEndElement();
????????????????????writer.WriteEndDocument();
????????????????????//Flush?the?object?and?write?the?XML?data?to?the?file
????????????????????writer.Flush();
????????????????????return?true;
????????????????}

????????????}
????????}
????????public?bool?Write(Exception?ex)
????????{
????????????Write(ex.Message);
????????????return?true;

????????}
????}

?

?

?

?

App.config配置
<?xml?version="1.0"?encoding="utf-8"??>
<configuration>
??<appSettings>
????<add?key="LogType"?value="LogClassLibrary.TextFileLog"/>
????<!--
????本程序集配置
????<add?key="LogType"?value="ConsoleApplication2.Log例子.TextFileLog"/>
????-->
????<!--?XmlFileLog??TextFileLog-->
????<add?key="LogTarget"?value="c:\log.txt"/>
??</appSettings>
</configuration>

?

?

?

?

主程序
?public?static?void?Main()
????????{
????????????#region?同程序集下
????????????System.Type?type?=?System.Type.GetType(ConfigurationManager.AppSettings["LogType"].ToString());
????????????ILog?log?=?(ILog)Activator.CreateInstance(type);
????????????log.Write(new?Exception("異常測試"));
????????????#endregion
????????}

?

?

如果在不同的程序集下，那主函數(shù)和配置會略有不同

?

?

不同程序集主函數(shù)
?public?static?void?Main()
????????{

????????????#region?不同程序集
????????????string?assemblyPath?=?Path.Combine(Environment.CurrentDirectory,?"LogClassLibrary.dll");
????????????Assembly?a?=?Assembly.LoadFrom(assemblyPath);
????????????Type?type?=?a.GetType(ConfigurationManager.AppSettings["LogType"].ToString());
????????????LogClassLibrary.ILog?log?=?(LogClassLibrary.ILog)type.InvokeMember(null,BindingFlags.CreateInstance,null,null,null);
????????????log.Write(new?Exception("異常測試"));
????????????#endregion


????????}

?

?

這部分源碼下載

源碼下載

2、插件編程技術(shù)
插件是指遵循一定的接口規(guī)范、可以動態(tài)加載和運(yùn)行的程序模塊。從上面的例子可以看出，通過反射可以非常方便的動態(tài)加載程序集。因此，利用反射的動態(tài)加載代碼能力，可以很容易的實現(xiàn)插件。插件編程的要點是使用接口來定義插件的功能特征。插件的宿主程序通過接口來確認(rèn)、裝載和執(zhí)行插件的功能，實現(xiàn)插件功能的所有類都必須實現(xiàn)定義插件的接口。

這里只是選貼一部分代碼，詳細(xì)分析請看源碼

結(jié)構(gòu)圖

?

接口部分

?

?

接口
public?interface?IHost
????{
????????List<ILog>?Plugins?{?get;?}
????????int?LoadPlugins(string?path);
????????ILog?GetLog(string?name);

????}
?public?interface?ILog
????{
????????bool?Write(string?message);
????????bool?Write(Exception?ex);

????}

?

?

宿主實現(xiàn)

?

?

宿主實現(xiàn)
?public?class?Host?:?IHost
????{
????????private?List<ILog>?plugins?=?new?List<ILog>();
????????#region?IHost?成員

????????public?List<ILog>?Plugins
????????{
????????????get?{?return?plugins;?}
????????}

????????public?int?LoadPlugins(string?path)
????????{
????????????string[]?assemblyFiles?=?Directory.GetFiles(path,?"*.dll");
????????????foreach?(var?file?in?assemblyFiles)
????????????{
????????????????Assembly?assembly?=?Assembly.LoadFrom(file);
????????????????foreach?(var?type?in?assembly.GetExportedTypes())
????????????????{
????????????????????if?(type.IsClass?&&?typeof(ILog).IsAssignableFrom(type))
????????????????????{
????????????????????????ILog?plugin?=?Activator.CreateInstance(type)?as?ILog;
????????????????????????plugins.Add(plugin);

????????????????????}
????????????????}
????????????}
????????????return?plugins.Count;
????????}

????????public?ILog?GetLog(string?name)
????????{
????????????foreach?(var?item?in?plugins)
????????????{
????????????????if?(item.GetType().ToString()==name)
????????????????{
????????????????????return?item;
????????????????}
????????????????
????????????}
????????????return?null;
????????}

????????#endregion
????}

?

?

ILog的實現(xiàn)和上例基本一樣，請參考

主程序代碼

?

?

主程序代碼
static?void?Main(string[]?args)
????????{
????????????Host.Host?host?=?new?Host.Host();
????????????host.LoadPlugins(".");
????????????InterfaceLayer.ILog?log?=?host.GetLog(ConfigurationManager.AppSettings["LogType"].ToString());
????????????log.Write(new?Exception("異常測試"));
????????}

?

?

插件編程源碼下載

源碼下載

3、分析對象，得到對象中的屬性值
大家使用應(yīng)都用過asp.net中的DropdownList，在綁定其值的時候絕大多數(shù)情況下我們做的都是同樣的事情，獲得數(shù)據(jù)源，根據(jù)數(shù)據(jù)源中的某些列綁定控件，下邊我們來說說通用情況的處理方式。我們只需要提供數(shù)據(jù)集合，以及需要綁定到控件的兩個屬性（text，value）名即可。

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Code

轉(zhuǎn)載于:https://www.cnblogs.com/strivers/archive/2010/11/27/1889744.html

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