SharpDevelop中Addin插件系统的详解(一)
相信会有很多的Programmer们对换“插件”这一术语都会抱有很大的兴趣，而#SharpDevelopr中的插件系统正以它较大的灵活性、可扩展性吸引了从多Programmer的目光。
（关于#SharpDevelop源码，可以去http://sourceforge.com下载。）
1. 服务概念与Addin插件系统的结合
在剖析Addin插件系统之前，我们还是要首先来了解一下#SharpDevelop中的Service（服务）概念，这也正是基于#SharpDevelop的Addin插件系统与Service服务紧密结合所作出一种考虑。
在剖析Addin插件系统之前，我们还是要首先来了解一下#SharpDevelop中的Service（服务）概念，这也正是基于#SharpDevelop的Addin插件系统与Service服务紧密结合所作出一种考虑。
#SharpDevelop中的服务，是指用于提供一些诸如“OpenFile”功能的类。在#SharpDevelop中，为了保证这些服务类的可替换性、可扩展性以及服务类的简单定位功能，引入了用于管理这些服务类的ServiceManager类。由于该ServiceManager类采用了Singleton设计模式，从而保证了在#SharpDevelop的任一部分均可方便地获取、使用这些服务类。
以下为与服务概念相关的一些源码，读者可从SharpDevelop\src\Main\Core\Services、SharpDevelop\src\Main\Base\Services中获取。
////////////////////////////////////////////////////////////////////////////////////////////////////////////////
public class ServiceManager
{
ArrayList serviceList = new ArrayList();
Hashtable servicesHashtable = new Hashtable();
// Singleton design pattern.
static ServiceManager defaultServiceManager = new ServiceManager();
/// <summary>
/// Gets the default ServiceManager
/// </summary>
public static ServiceManager Services
{
Get { return defaultServiceManager; }
}
/// <summary>
/// Don't create ServiceManager objects, only have ONE per application.
/// </summary>
private ServiceManager()
{
// add 'core' services
AddService(new PropertyService());
AddService(new StringParserService());
AddService(new FileUtilityService());
}
/// <remarks>
/// This method initializes the service system to a path inside the add-in tree.
/// This method must be called ONCE.
/// </remarks>
public void InitializeServicesSubsystem(string servicesPath)
{
// add add-in tree services
AddServices((IService[])AddInTreeSingleton.AddInTree.GetTreeNodeservicesPath).BuildChildItems(this).ToArray(typeof(IService)));
// initialize all services
foreach (IService service in serviceList)
{
DateTime now = DateTime.Now;
service.InitializeService();
}
}
/// <remarks>
/// Calls UnloadService on all services. This method must be called ONCE.
/// </remarks>
public void UnloadAllServices()
{
foreach (IService service in serviceList)
{
service.UnloadService();
}
}
public void AddService(IService service)
{
serviceList.Add(service);
}
public void AddServices(IService[] services)
{
foreach (IService service in services)
{
AddService(service);
}
}
// HACK: MONO BUGFIX
// this doesn't work on mono:serviceType.IsInstanceOfType(service)
bool IsInstanceOfType(Type type, IService service)
{
Type serviceType = service.GetType();
foreach (Type iface in serviceType.GetInterfaces())
{
if (iface == type)
{
return true;
}
}
while (serviceType != typeof(System.Object))
{
if (type == serviceType)
{
return true;
}
serviceType = serviceType.BaseType;
}
return false;
}
/// <remarks>
/// Requestes a specific service, may return null if this service is not found.
/// </remarks>
public IService GetService(Type serviceType)
{
IService s = (IService)servicesHashtable[serviceType];
if (s != null)
{
return s;
}
foreach (IService service in serviceList)
{
if (IsInstanceOfType(serviceType, service))
{
servicesHashtable[serviceType] = service;
return service;
}
}
return null;
}
}
///////////////////////////////////////////////////////////////////////////////////////////////////////////////
/// <summary>
/// This interface must be implemented by all services.
/// </summary>
public interface IService
{
/// <summary>
/// This method is called after the services are loaded.
/// </summary>
void InitializeService();
/// <summary>
/// This method is called before the service is unloaded.
/// </summary>
void UnloadService();
event EventHandler Initialize;
event EventHandler Unload;
}
////////////////////////////////////////////////////////////////////////////////////////////////////////////////
值得我们关注的代码行有：
值得我们关注的代码行有：
// add add-in tree services
AddServices((IService[])AddInTreeSingleton.AddInTree.GetTreeNode(servicesPath).BuildChildItems(this).ToArray(typeof(IService)));
该语句将从Addin插件树中获取所要加载的所有服务类，并将这些服务类初始化后加入到服务管理容器中。由于Addin插件树是根据一系列的*.Addin文件创建的，所以它具有很强的可替换性、可扩展性。
同时，通过ServiceManager类的Service GetService(Type serviceType)方法，可以很轻易地获取服务管理容器中的任意类型的服务类。
例如，要获取服务管理容器中的IMessageService类，可经以下语句获取：
IMessageService servicer = (IMessageService)ServiceManager.Services.GetService(typeof(IMessageService));
（未完待续）
（未完待续）
