AOP in Dotnet core : Dynamic Proxy with Real Proxy in Dotnet core

Question

I am migrating my application from .Net Framework 4.5.1 to Dot Net Core. I was using RealProxy Class for logging user information and parameters on BeforeExecute and AfterExecute ( like this link)

Now it seems there is no such a thing in Dot core.Plus I don't want to use third parties.I found this link that is using Actionfilter but it won't do the job.

my question is How can I implement Dynamic Proxy in Dot net Core? Is there any alternate for RealProxy Class?

Answer 1

As I already answered in RealProxy in dotnet core?, RealProxy doesn't exist in .NET Core.

An alternative is the DispatchProxy, which has a wonderful example here: http://www.c-sharpcorner.com/article/aspect-oriented-programming-in-c-sharp-using-dispatchproxy/.

If we simplify the code, this is what we get:

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");
    }
}

So if we have an example class Calculator with a corresponding interface (not shown here):

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

we can simply use it like this

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

And you will get the desired logging.