在dotnet核心中使用RealProxy？

Question

我正在使用C#中面向方面程序设计的名称空间System.Runtime.Remoting.Proxies和System.Runtime.Remoting.Messaging。我正在尝试将我的应用程序从.Net Framework4.6移植到dnxcore/dotnet。

智能感知说，这两个名称空间在我的框架-vesion (netcoreapp1.0 / dnxcore50)中是不可用的。知道这两个名称空间是否会出现吗？或者知道如何像RealProxy-class一样实现面向方面编程？

我不想使用第三方库-我只想使用.Net提供给我的库。

Answer 1

It looks like RealProxy won't come to .NET Core/Standard。在这一期中，微软的一位开发人员建议DispatchProxy作为替代方案。

此外，一些现有的面向方面程序设计框架可能已经或将来支持.NET核心(如对该问题的评论中所示)。

另一种选择是DispatchProxy，它在这里有一个很好的例子：http://www.c-sharpcorner.com/article/aspect-oriented-programming-in-c-sharp-using-dispatchproxy/。

如果我们简化代码，我们会得到如下结果：

public class LoggingDecorator<T> : DispatchProxy
{
    private T _decorated;

    protected override object Invoke(MethodInfo targetMethod, object[] args)
    {
        try
        {
            LogBefore(targetMethod, args);

            var result = targetMethod.Invoke(_decorated, args);

            LogAfter(targetMethod, args, result);
            return result;
        }
        catch (Exception ex) when (ex is TargetInvocationException)
        {
            LogException(ex.InnerException ?? ex, targetMethod);
            throw ex.InnerException ?? ex;
        }
    }

    public static T Create(T decorated)
    {
        object proxy = Create<T, LoggingDecorator<T>>();
        ((LoggingDecorator<T>)proxy).SetParameters(decorated);

        return (T)proxy;
    }

    private void SetParameters(T decorated)
    {
        if (decorated == null)
        {
            throw new ArgumentNullException(nameof(decorated));
        }
        _decorated = decorated;
    }

    private void LogException(Exception exception, MethodInfo methodInfo = null)
    {
        Console.WriteLine($"Class {_decorated.GetType().FullName}, Method {methodInfo.Name} threw exception:\n{exception}");
    }

    private void LogAfter(MethodInfo methodInfo, object[] args, object result)
    {
        Console.WriteLine($"Class {_decorated.GetType().FullName}, Method {methodInfo.Name} executed, Output: {result}");
    }

    private void LogBefore(MethodInfo methodInfo, object[] args)
    {
        Console.WriteLine($"Class {_decorated.GetType().FullName}, Method {methodInfo.Name} is executing");
    }
}

因此，如果我们有一个具有相应接口的示例类Calculator (此处未显示)：

public class Calculator : ICalculator
{
    public int Add(int a, int b)
    {
        return a + b;
    }
}

我们可以像这样简单地使用它

static void Main(string[] args)
{
    var decoratedCalculator = LoggingDecorator<ICalculator>.Create(new Calculator());
    decoratedCalculator.Add(3, 5);
    Console.ReadKey();
}

Answer 2

您可以使用System.Reflection.DispatchProxy或您自己的简单装饰器实现。请查看维基百科上的Decorator pattern页面以获取实现示例。

目前在.NET核心中，你不能在DispatchProxy中使用构造函数注入。您必须使用DispatchProxy.Create()工厂方法和属性注入，并显式转换为要使用的代理类型。有关更多信息，请查看.NET核心GitHub存储库中的DispachProxyTest.cs。

这是一个继承DispatchProxy的简单泛型装饰器的示例

class GenericDecorator : DispatchProxy
{
    public object Wrapped { get; set; }
    public Action<MethodInfo, object[]> Start { get; set; }
    public Action<MethodInfo, object[], object> End { get; set; }
    protected override object Invoke(MethodInfo targetMethod, object[] args)
    {
        Start?.Invoke(targetMethod, args);
        object result = targetMethod.Invoke(Wrapped, args);
        End?.Invoke(targetMethod, args, result);
        return result;
    }
}

以及它的用法：

class Program
{
    static void Main(string[] args)
    {
        IEcho toWrap = new EchoImpl();
        IEcho decorator = DispatchProxy.Create<IEcho, GenericDecorator>();
        ((GenericDecorator)decorator).Wrapped = toWrap;
        ((GenericDecorator)decorator).Start = (tm, a) => Console.WriteLine($"{tm.Name}({string.Join(',', a)}) is started");
        ((GenericDecorator)decorator).End = (tm, a, r) => Console.WriteLine($"{tm.Name}({string.Join(',', a)}) is ended with result {r}");
        string result = decorator.Echo("Hello");
    }

    class EchoImpl : IEcho
    {
        public string Echo(string message) => message;
    }

    interface IEcho
    {
        string Echo(string message);
    }
}

Answer 3

您可以使用支持.Net内核的Castle.Core：

using Castle.DynamicProxy;
using System;
using System.Reflection;

namespace ObservableProxyTest
{
    class Program
    {
        private static readonly ProxyGenerator Generator = new ProxyGenerator();

        static void Main(string[] args)
        {
            var obj = new MyEntity()
            {
                Name = "My name",
                Description = "My description"
            };

            var proxy = Generator.CreateClassProxyWithTarget(obj, new ObservableInterceptor());

            Console.WriteLine("Object changed: " + proxy.IsChanged);

            proxy.Name = "My name 2";
            proxy.Description = "My description 2";

            Console.WriteLine("Object changed: " + proxy.IsChanged);

            Console.ReadLine();
        }
    }

    internal interface IObservable
    {
        bool IsChanged { get; }
        void SetChanged();
    }

    public abstract class BaseEntity : IObservable
    {
        public virtual bool IsChanged { get; protected set; }

        public void SetChanged()
        {
            IsChanged = true;
        }
    }

    public class MyEntity : BaseEntity
    {
        // Virtual keyword is very important
        public virtual string Name { get; set; }
        public virtual string Description { get; set; }
    }

    internal class ObservableInterceptor : IInterceptor
    {
        public void Intercept(IInvocation invocation)
        {
            var observable = invocation.InvocationTarget as IObservable;
            if (observable != null && !observable.IsChanged && IsSetter(invocation.Method))
            {
                observable.SetChanged();
            }
            invocation.Proceed();
        }

        private bool IsSetter(MethodInfo method)
        {
            return method.IsSpecialName && method.Name.StartsWith("set_", StringComparison.OrdinalIgnoreCase);
        }
    }

}

也请阅读非常好的文章：https://fullboarllc.com/change-tracking-structuremap-dynamicproxy/