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在.net中有了一个AppDomain——应用程序域的新概念，.NET程序通过AppDomain这个媒介来运行在进程中。
我们运行一个.NET应用程序或者一个运行库宿主时，OS会首先建立一个进程，然后会在进程中加载CLR(这个加载一般是通过调用_CorExeMain或者_CorBindToRuntimeEx方法来实现)，在加载CLR时会创建一个默认的AppDomain，它是CLR的运行单元，程序的Main方法就是在这里执行，这个默认的AppDomain是唯一且不能被卸载的，当该进程消灭时，默认AppDomain才会随之消失。
一个进程中可以有多个AppDomain，且它们直接是相互隔离的，我们的Assembly是不能单独执行的，它必须被加载到某个AppDomain中，要想卸载一个Assembly就只能卸载其AppDomain。
一旦Assembly被调用，在调用之前会将程序集加载到默认AppDomain，然后执行，我们就会遇到这个问题：如果我需要做替换或者删除Assembly等这些操作的时候，由于Assembly已经被默认AppDomain加载，那么对它的更改肯定是不允许的，它会弹出这样的错误：
无法删除WindowsApplication1: 访问被拒绝
请确定磁盘末被写保护 而且文件末被使用除非你关掉作业管理服务器，然后再操作，显然这样做是很不合理的。
并且默认AppDomain是不能被卸载的，那么我们该怎么办呢，我想到的方法是动态的加载Assembly，新建一个AppDomain，让Assembly加载到这个新AppDomain中然后执行，当执行完后卸载这个新的AppDomain即可。核心思想就是：如果程序集被加载到默认应用程序域中，则当进程运行时将无法从内存中卸载该程序集。但是，如果打开另一个应用程序域来加载和执行程序集，则卸载该应用程序域时也会同时卸载程序集。使用此技术最小化长时间运行的进程的工作集。，方法如下：
1、创建程序集加载类AssemblyDynamicLoader，该类用来创建新的AppDomain，并生成用来执行.net程序的RemoteLoader类:
Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/--> using System; using System.Collections.Generic; using System.Globalization; using System.IO; using System.Reflection; using System.Text; using Ark.Log; /// /// The local loader. /// public class AssemblyDynamicLoader{ /// /// The log util. /// private static ILog log = LogManager.GetLogger( typeof (AssemblyDynamicLoader)); /// /// The new appdomain. /// private AppDomain appDomain; /// /// The remote loader. /// private RemoteLoader remoteLoader; /// /// Initializes a new instance of the class. /// public AssemblyDynamicLoader() { AppDomainSetup setup = new AppDomainSetup(); setup.ApplicationName = " ApplicationLoader " ; setup.ApplicationBase = AppDomain.CurrentDomain.BaseDirectory; setup.PrivateBinPath = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, " private " ); setup.CachePath = setup.ApplicationBase; setup.ShadowCopyFiles = " true " ; setup.ShadowCopyDirectories = setup.ApplicationBase; this .appDomain = AppDomain.CreateDomain( " ApplicationLoaderDomain " , null , setup); String name = Assembly.GetExecutingAssembly().GetName().FullName; this .remoteLoader = (RemoteLoader) this .appDomain.CreateInstanceAndUnwrap(name, typeof (RemoteLoader).FullName); } /// /// Invokes the method. /// /// The full name. /// Name of the class. /// The args input. /// Name of the program. /// The output of excuting. public String InvokeMethod(String fullName, String className, String argsInput, String programName) { this .remoteLoader.InvokeMethod(fullName, className, argsInput, programName); return this .remoteLoader.Output; } /// /// Unloads this instance. /// public void Unload() { try { AppDomain.Unload( this .appDomain); this .appDomain = null ; } catch (CannotUnloadAppDomainException ex) { log.Error( " To unload assembly error! " , ex); } }} 2、创建RemoteLoader类，它可以在AppDomain中自由穿越，这就需要继承System.MarshalByRefObject这个抽象类，这里RemoteLoader如果不继承MarshalByRefObject类则一定会报错(在不同AppDomain间传递对象，该对象必须是可序列化的)。以RemoteLoader类做为代理来调用待执行的.net程序。
Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/--> using System; using System.Collections.Generic; using System.Globalization; using System.IO; using System.Reflection; using System.Text; /// /// The Remote loader. /// public class RemoteLoader : MarshalByRefObject{ /// /// The assembly we need. /// private Assembly assembly = null ; /// /// The output. /// private String output = String.Empty; /// /// Gets the output. /// /// The output. public String Output { get { return this .output; } } /// /// Invokes the method. /// /// The full name. /// Name of the class. /// The args input. /// Name of the program. public void InvokeMethod(String fullName, String className, String argsInput, String programName) { this .assembly = null ; this .output = String.Empty; try { this .assembly = Assembly.LoadFrom(fullName); Type pgmType = null ; if ( this .assembly != null ) { pgmType = this .assembly.GetType(className, true , true ); } else { pgmType = Type.GetType(className, true , true ); } Object[] args = RunJob.GetArgs(argsInput); BindingFlags defaultBinding = BindingFlags.DeclaredOnly | BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.IgnoreCase | BindingFlags.InvokeMethod | BindingFlags.Static; CultureInfo cultureInfo = new CultureInfo( " es-ES " , false ); try { MethodInfo methisInfo = RunJob.GetItsMethodInfo(pgmType, defaultBinding, programName); if (methisInfo == null ) { this .output = " EMethod does not exist! " ; } if (methisInfo.IsStatic) { if (methisInfo.GetParameters().Length == 0 ) { if (methisInfo.ReturnType == typeof ( void )) { pgmType.InvokeMember(programName, defaultBinding, null , null , null , cultureInfo); this .output = " STo call a method without return value successful. " ; } else { this .output = (String)pgmType.InvokeMember(programName, defaultBinding, null , null , null , cultureInfo); } } else { if (methisInfo.ReturnType == typeof ( void )) { pgmType.InvokeMember(programName, defaultBinding, null , null , args, cultureInfo); this .output = " STo call a method without return value successful. " ; } else { this .output = (String)pgmType.InvokeMember(programName, defaultBinding, null , null , args, cultureInfo); } } } else { if (methisInfo.GetParameters().Length == 0 ) { object pgmClass = Activator.CreateInstance(pgmType); if (methisInfo.ReturnType == typeof ( void )) { pgmType.InvokeMember(programName, defaultBinding, null , pgmClass, null , cultureInfo); this .output = " STo call a method without return value successful. " ; } else { this .output = (String)pgmType.InvokeMember(programName, defaultBinding, null , pgmClass, null , cultureInfo); // 'ymtpgm' is program's name and the return value of it must be started with 'O'. } } else { object pgmClass = Activator.CreateInstance(pgmType); if (methisInfo.ReturnType == typeof ( void )) { pgmType.InvokeMember(programName, defaultBinding, null , pgmClass, args, cultureInfo); this .output = " STo call a method without return value successful. " ; } else { this .output = (String)pgmType.InvokeMember(programName, defaultBinding, null , pgmClass, args, cultureInfo); // 'ymtpgm' is program's name and the return value of it must be started with 'O'. } } } } catch { this .output = (String)pgmType.InvokeMember(programName, defaultBinding, null , null , null , cultureInfo); } } catch (Exception e) { this .output = " E " + e.Message; } }} 其中的InvokeMethod方法只要提供Assembly的全名、类的全名、待执行方法的输入参数和其全名就可以执行该方法，该方法可以是带参数或不带参数，静态的或者不是静态的。
最后这样使用这两个类：
Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/--> AssemblyDynamicLoader loader = new AssemblyDynamicLoader(); String output = loader.InvokeMethod( " fileName " , " ymtcla " , " yjoinp " , " ymtpgm " ); loader.Unload();
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