PostSharp Fundamentals

Some example code and notes created while taking the PostSharp Fundamentals course on PluralSight.

Aspect Oriented Programming

Overview of Aspect Oriented Progamming (AOP).

What is it?

• Managing code in "cross cutting" concerns
• Increasing the modularity of our codebase
• Composition of code infrastructure concerns
• Examples: Autiting, Logging, Security (Authentication Authorization), Perf. Monitoring, etc.

Why would you use it?

• Reduce code duplication
• Keep code singly responsible (SRP - S in SOLID)
• DRY code
• Modularity

How can you apply it?

• Two main ways: Interceptors and IL Weaving

  • Interceptors:
    • Basic Decorator Pattern
    • Commonly implemented through IoC containers
  • IL Weaving:
    • Much more complex possibilities
    • Requires a post compile step
    • PostSharp is an example of an IL Weaving AOP framework

Post Sharp

Installation & Setup

• Can either install via MSI/EXE or NuGet (most popular)
• Licenses - for larger organizations consider setting up license server (ala Resharper)

Out of the box Aspects

Starting point for aspect development.

• Existing Aspects built into PostSharp
• Majority use overrides to provide advices to the target ```
• Decorator pattern is everywhere

OnMethodBoundaryAspect

This is a method level apsect. There are a number of "point cuts" that can be implemented for a method level aspect.

• Point Cuts:
  • OnEntry
  • OnExit
  • OnException
  • OnSuccess
• Maps to a full decorator pattern implementation when all four (4) overrides are used

Structure of the OnMethodBoundaryAspect:

...

{
    OnEntry();

    try
    {
        TargetCode();
        OnSuccess();
    }
    catch (Exception ex)
    {
        OnException();
    }
    finally
    {
        OnExit();
    }
}

...

MethodExecuteArgs Class

Three (3) items that you will commonly interact with that come from the MethodExecuteArgs class.

• Arguments
  • List of value being passed to the target method
  • List of object values; not names or properties of the parameters (distinct from Parameters)
• Method
  • Meta-data information about the target
    • ex. GetParameters() - returns meta-data about the parameters
  • Reflection-based
• ReturnValue
  • Null if method is Void