Aop即是面向切面编程,众多Aop框架里Castle是最为人所知的,另外还有Autofac、还有死去的Spring.NET,当然,.NET Core社区新秀AspectCore在性能与功能上都非常优秀,已经逐渐被社区推崇和有越来越多的人使用。感谢柠檬同学的礼物!
如果大家出于自身需求或者学习,想实现一个Aop,是不是觉得一来就要使用Emit去做?最近我了解到了System.Reflection.DispatchProxy这个corefx类库,已经实现了动态代理功能。
下面演示一下它的使用方法:
class Program
{
static void Main(string[] args)
{
//创建代理类,并把SamepleProxy作为拦截器注入
var samepleProxy = (targetInterface)SamepleProxy.Create<targetInterface, SamepleProxy>();
//执行接口方法
samepleProxy.Write("here is invoke by proxy");
}
}
//需要被生成代理实例的接口
public interface targetInterface
{
//这个方法会被代理类实现
void Write(string writesomeshing);
}
public class SamepleProxy : DispatchProxy
{
/// <summary>
/// 拦截调用
/// </summary>
/// <param name="method">所拦截的方法信息</param>
/// <param name="parameters">所拦截方法被传入的参数指</param>
/// <returns></returns>
protected override object Invoke(MethodInfo targetMethod, object[] args)
{
Console.WriteLine(args[0]);
return null;
}
}
System.Reflection.DispatchProxy
只有一个Api,就是objecct Create<T,TProxy>() where TProxy:DispatchProxy
,约束了只能传入泛型参数,并不能从方法传入类型,这就会带来很多问题。而更可气的是,给官方提了issue之后,还是不给增加这个api……
幸好,在那个issue下,issue作者提供了一个解决方案,就是用反射来构造这个泛型方法。我还在这基础上,封装了一下,加入了传入拦截器实例和传入拦截器构造方法参数的功能。
/// <summary>
/// 拦截器接口
/// </summary>
public interface IInterceptor
{
/// <summary>
/// 拦截器调用
/// </summary>
/// <param name="target">代理实例</param>
/// <param name="method">所拦截的方法</param>
/// <param name="parameters">所拦截方法传入的参数值</param>
/// <returns>返回值会传递给方法返回值</returns>
object Intercept(object target, MethodInfo method, object[] parameters);
}
拦截器要实现这个接口,下面是对DispatchProxy的封装,实现更多创建代理实例的方法
public class ProxyGenerator : DispatchProxy
{
private IInterceptor interceptor { get; set; }
private static object proxy { get; set; }
/// <summary>
/// 创建代理实例
/// </summary>
/// <param name="targetType">所要代理的接口类型</param>
/// <param name="interceptor">拦截器</param>
/// <returns>代理实例</returns>
public static object Create(Type targetType, IInterceptor interceptor)
{
object proxy = GetProxy(targetType);
MethodInfo method = typeof(ProxyGenerator).GetMethod(nameof(CreateInstance), BindingFlags.NonPublic | BindingFlags.Instance, Type.DefaultBinder, new[] { typeof(IInterceptor) }, null);
method.Invoke(proxy, new object[] { interceptor });
return proxy;
}
/// <summary>
/// 创建代理实例
/// </summary>
/// <param name="targetType">所要代理的接口类型</param>
/// <param name="interceptorType">拦截器类型</param>
/// <param name="parameters">拦截器构造函数参数值</param>
/// <returns>代理实例</returns>
public static object Create(Type targetType, Type interceptorType, params object[] parameters)
{
object proxy = GetProxy(targetType);
MethodInfo method = typeof(ProxyGenerator).GetMethod(nameof(CreateInstance), BindingFlags.NonPublic | BindingFlags.Instance, Type.DefaultBinder, new[] { typeof(Type), typeof(object[]) }, null);
method.Invoke(proxy, new object[] { interceptorType, parameters });
return proxy;
}
/// <summary>
/// 创建代理实例 TTarget:所要代理的接口类型 TInterceptor:拦截器类型
/// </summary>
/// <param name="parameters">拦截器构造函数参数值</param>
/// <returns>代理实例</returns>
public static TTarget Create<TTarget, TInterceptor>(params object[] parameters) where TInterceptor : IInterceptor
{
object proxy = GetProxy(typeof(TTarget));
MethodInfo method = typeof(ProxyGenerator).GetMethod(nameof(CreateInstance), BindingFlags.NonPublic | BindingFlags.Instance, Type.DefaultBinder, new[] { typeof(Type), typeof(object[]) }, null);
method.Invoke(proxy, new object[] { typeof(TInterceptor), parameters });
return (TTarget)proxy;
}
private static object GetProxy(Type targetType)
{
MethodInfo method = typeof(DispatchProxy).GetMethod(nameof(DispatchProxy.Create), new Type[] { });
method = method.MakeGenericMethod(targetType, typeof(ProxyGenerator));
proxy = method.Invoke(null, null);
return proxy;
}
private void CreateInstance(Type interceptorType, object[] parameters)
{
this.interceptor = (IInterceptor)Activator.CreateInstance(interceptorType, parameters);
}
private void CreateInstance(IInterceptor interceptor)
{
this.interceptor = interceptor;
}
protected override object Invoke(MethodInfo method, object[] parameters)
{
return this.interceptor.Intercept(proxy, method, parameters);
}
}
使用方法:
class Program
{
static void Main(string[] args)
{
// var poxy = (targetInterface)ProxyGenerator.Create(typeof(targetInterface), new SamepleProxy());
// 或
//var poxy = (targetInterface)ProxyGenerator.Create(typeof(targetInterface), typeof(SamepleProxy));
// 或
var poxy = ProxyGenerator.Create<targetInterface, SamepleProxy>();
poxy.Write("here is invoked by coreproxy");
}
}
public class SamepleProxy : IInterceptor
{
public object Intercept(object target, MethodInfo method, object[] parameters)
{
Console.WriteLine(parameters[0]);
return null;
}
}
public interface targetInterface
{
void Write(string writesome);
}
总结一下就是,微软爸爸给我们的这个轮子还是即轻便又很好用的。
本文的实例代码可以在我的github上找到:https://github.com/ElderJames/CoreProxy