C# 有关Assembly.Unload详解

using System;
using System.Reflection;
using System.Collections;

namespace Loader{

/* contains assembly loader objects, stored in a hash
* and keyed on the .dll file they represent. Each assembly loader
* object can be referenced by the original name/path and is used to
* load objects, returned as type Object. It is up to the calling class
* to cast the object to the necessary type for consumption.
* External interfaces are highly recommended!!
* */
public class ObjectLoader : IDisposable {

// essentially creates a parallel-hash pair setup
// one appDomain per loader
protected Hashtable domains = new Hashtable();
// one loader per assembly DLL
protected Hashtable loaders = new Hashtable();

public ObjectLoader() {/*...*/}

public object GetObject( string dllName, string typeName, object[] constructorParms ){
Loader.AssemblyLoader al = null;
object o = null;
try{
al = (Loader.AssemblyLoader)loaders[ dllName ];
} catch (Exception){}
if( al == null ){
AppDomainSetup setup = new AppDomainSetup();
setup.ShadowCopyFiles = "true";
AppDomain domain = AppDomain.CreateDomain( dllName, null, setup );
domains.Add( dllName, domain );
object[] parms = { dllName };
// object[] parms = null;
BindingFlags bindings = BindingFlags.CreateInstance | BindingFlags.Instance | BindingFlags.Public;
try{
al = (Loader.AssemblyLoader)domain.CreateInstanceFromAndUnwrap(
"Loader.dll", "Loader.AssemblyLoader", true, bindings, null, parms, null, null, null
);
} catch (Exception){
throw new AssemblyLoadFailureException();
}
if( al != null ){
if( !loaders.ContainsKey( dllName ) ){
loaders.Add( dllName, al );
} else {
throw new AssemblyAlreadyLoadedException();
}
} else {
throw new AssemblyNotLoadedException();
}
}
if( al != null ){
o = al.GetObject( typeName, constructorParms );
if( o != null && o is AssemblyNotLoadedException ){
throw new AssemblyNotLoadedException();
}
if( o == null || o is ObjectLoadFailureException ){
string msg = "Object could not be loaded. Check that type name " + typeName +
" and constructor parameters are correct. Ensure that type name " + typeName +
" exists in the assembly " + dllName + ".";
throw new ObjectLoadFailureException( msg );
}
}
return o;
}

public void Unload( string dllName ){
if( domains.ContainsKey( dllName ) ){
AppDomain domain = (AppDomain)domains[ dllName ];
AppDomain.Unload( domain );
domains.Remove( dllName );
}
}

~ObjectLoader(){
dispose( false );
}

public void Dispose(){
dispose( true );
}

private void dispose( bool disposing ){
if( disposing ){
loaders.Clear();
foreach( object o in domains.Keys ){
string dllName = o.ToString();
Unload( dllName );
}
domains.Clear();
}
}
}

}

using System;
using System.Reflection;

namespace Loader {
// container for assembly and exposes a GetObject function
// to create a late-bound object for casting by the consumer
// this class is meant to be contained in a separate appDomain
// controlled by ObjectLoader class to allow for proper encapsulation
// which enables proper shadow-copying functionality.
internal class AssemblyLoader : MarshalByRefObject, IDisposable {

#region class-level declarations
private Assembly a = null;
#endregion

#region constructors and destructors
public AssemblyLoader( string fullPath ){
if( a == null ){
a = Assembly.LoadFrom( fullPath );
}
}
~AssemblyLoader(){
dispose( false );
}

public void Dispose(){
dispose( true );
}

private void dispose( bool disposing ){
if( disposing ){
a = null;
System.GC.Collect();
System.GC.WaitForPendingFinalizers();
System.GC.Collect( 0 );
}
}
#endregion

#region public functionality
public object GetObject( string typename, object[] ctorParms ){
BindingFlags flags = BindingFlags.CreateInstance | BindingFlags.Instance | BindingFlags.Public;
object o = null;
if( a != null ){
try{
o = a.CreateInstance( typename, true, flags, null, ctorParms, null, null );
} catch (Exception){
o = new ObjectLoadFailureException();
}
} else {
o = new AssemblyNotLoadedException();
}
return o;
}
public object GetObject( string typename ){
return GetObject( typename, null );
}
#endregion

}
}