How to Implement Dynamic Proxies in C#

Dynamic proxies in C# are a powerful tool that allow developers to create proxy instances of interfaces or classes at runtime. These proxies enable developers to intercept method calls and add custom behavior before or after the method execution. Implementing dynamic proxies in C# involves using libraries like Castle DynamicProxy or LinFu, which provide APIs for creating proxies and defining interceptors. By utilizing dynamic proxies, developers can easily apply cross-cutting concerns such as logging, caching, and security without modifying the original codebase.

In this tutorial, you will learn how to implement dynamic proxies in C#. Dynamic proxies allow you to create objects that intercept method calls, allowing you to add additional functionality before or after the method is executed. This can be useful in scenarios such as logging, caching, or implementing AOP (Aspect-Oriented Programming) in your applications.

Table of Contents

Implementing Dynamic Proxies in C# – Examples

Let’s start by looking at some examples of how to implement dynamic proxies in C#.

Example 1: Creating a Simple Dynamic Proxy

To create a dynamic proxy in C#, you can use the RealProxy class from the System.Runtime.Remoting.Proxies namespace. Here’s an example:


using System;
using System.Runtime.Remoting.Proxies;
using System.Runtime.Remoting.Messaging;

public class LoggingProxy<T> : RealProxy
{
    private readonly T _target;

    public LoggingProxy(T target) : base(typeof(T))
    {
        _target = target;
    }

    public override IMessage Invoke(IMessage msg)
    {
        // Add logging logic here before the method is called

        var methodCall = (IMethodCallMessage)msg;
        var result = methodCall.MethodBase.Invoke(_target, methodCall.Args);

        // Add logging logic here after the method is called

        return new ReturnMessage(result, null, 0, methodCall.LogicalCallContext, methodCall);
    }
}

public interface ICalculator
{
    int Add(int a, int b);
}

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

public static void Main()
{
    ICalculator calculator = new LoggingProxy<ICalculator>(new Calculator()).GetTransparentProxy() as ICalculator;
    int result = calculator.Add(5, 10);
    Console.WriteLine(result);
}

In this example, we create a LoggingProxy class that inherits from RealProxy and implements the Invoke method. The Invoke method is called for every method call made through the dynamic proxy. Inside this method, you can add your custom logic before and after the method is called.

Example 2: Adding Validation to a Dynamic Proxy

Another use case for dynamic proxies is to add validation to method calls. Here’s an example:


using System;
using System.Runtime.Remoting.Proxies;
using System.Runtime.Remoting.Messaging;

public class ValidationProxy<T> : RealProxy
{
    private readonly T _target;

    public ValidationProxy(T target) : base(typeof(T))
    {
        _target = target;
    }

    public override IMessage Invoke(IMessage msg)
    {
        var methodCall = (IMethodCallMessage)msg;

        // Add validation logic here before the method is called

        // Assuming the first argument is the integer to validate
        var argument = (int)methodCall.Args[0];
        if (argument < 0)
        {
            throw new ArgumentException("Argument must be a positive integer.");
        }

        var result = methodCall.MethodBase.Invoke(_target, methodCall.Args);

        // Add validation logic here after the method is called

        return new ReturnMessage(result, null, 0, methodCall.LogicalCallContext, methodCall);
    }
}

public interface ICalculator
{
    int Add(int a, int b);
}

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

public static void Main()
{
    ICalculator calculator = new ValidationProxy<ICalculator>(new Calculator()).GetTransparentProxy() as ICalculator;
    int result = calculator.Add(-5, 10);
    Console.WriteLine(result);
}

In this example, we create a ValidationProxy class that intercepts the Add method call and performs validation on the first argument. If the argument is less than 0, we throw an ArgumentException. Otherwise, the method is executed as usual. This way, we can ensure that the method is always called with valid arguments.

Best Practices for Implementing Dynamic Proxies in C#

When implementing dynamic proxies in C#, here are some best practices to keep in mind:

Keep the proxy logic separate from your business logic: It’s important to separate the proxy logic from your business logic to maintain a clear separation of concerns. This allows you to modify or remove the proxy without affecting the underlying functionality.
Use interfaces for proxy classes: To make your dynamic proxies more flexible, it’s recommended to use interfaces for the proxy classes. This allows you to easily switch between different implementations or apply the proxy to different types without changing the calling code.
Consider using existing libraries: While it’s possible to create dynamic proxies from scratch, there are existing libraries available that provide ready-to-use solutions, such as Castle DynamicProxy or Unity Interception. These libraries offer additional features and optimizations that can simplify your implementation.
Test your proxies thoroughly: As with any code, it’s important to thoroughly test your dynamic proxies to ensure they work as expected. Make sure to test different scenarios and edge cases to cover all possible use cases.

Implementing Dynamic Proxies in C# – Tips

Here are some helpful tips for implementing dynamic proxies in C#:

Understand the interception pipeline: When implementing dynamic proxies, it’s important to understand how the interception pipeline works. The interception pipeline determines the order in which interceptors are called and allows you to modify the behavior of the proxy.
Consider performance implications: Dynamic proxies can introduce overhead due to the additional method calls and logic. Before using dynamic proxies extensively, make sure to consider the performance implications and evaluate whether the benefits outweigh the costs.
Keep the proxy logic simple: It’s generally recommended to keep the proxy logic simple and focused on a specific concern. This makes the proxy easier to understand, maintain, and debug.

Implementing Dynamic Proxies in C# – Conclusion

In this tutorial, you have learned how to implement dynamic proxies in C#. You have seen examples of how to create simple proxies, add validation to method calls, and some best practices and tips for implementing dynamic proxies effectively.

Dynamic proxies can be a powerful tool in your software development toolbox, allowing you to add additional functionality to your applications without modifying the original code. By using dynamic proxies, you can achieve a higher level of flexibility, maintainability, and reusability in your codebase.

Implementing dynamic proxies in C# provides a powerful tool for creating flexible and customizable behavior in applications. By dynamically intercepting and handling method calls, developers can enhance the functionality of their code with ease. This technique offers a versatile way to add features such as logging, authentication, and validation, making it a valuable addition to any C# developer’s toolkit.