MVVM: When EventAggregator (aka MessageBus) is an Anti-Pattern

Very often we can see that developers tend to use static message buses for all kind of interactions between objects. For those, who unaware of this pattern I want to recall that this pattern allows organizing loosely coupled communication channel between objects which don’t want (or can’t) to know each other.
Let’s have a brief look at how a regular example of using this pattern may look like:

public class Sender {
    private readonly IEventAggregator eventAggregator;

    public Sender(IEventAggregator eventAggregator) {
        this.eventAggregator = eventAggregator;
    }

    public void Action() {
        eventAggregator.Publish(new Message());
    }
}

public class Receiver : IHandle<Message> {
    public Receiver(IEventAggregator eventAggregator) {
        eventAggregator.Subscribe(this);
    }
    public void Handle(Message message) {            
    }
}

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C# Static Code Analysis with NDepend

NDepend Icon
Have you heard about the “goto fail” fail? This is a security bug which was introduced by Apple in one of the iOS updates. Long story short, there was a piece of unreachable code which had to perform an important security check of a certificate. But it was unreachable. This is a huge defect in the software of this kind. Any meaningful static analysis tool would find that defect and any meaningful developer would fix such a bug after that. What am I talking about is that the cost of lately caught bugs is much greater than the cost of a bug caught at compile time. I don’t know how the hell Apple slipped up like that, but we are not going to discuss that. We are going to talk about static analysis.

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Learn Enterprise WPF with XAML from Scratch

My first course “Learn Enterprise WPF with XAML from Scratch” went live on Udemy.com and it you can buy it just for 10$! It is a great WPF tutorial for beginners!

In this course, you can learn deeply the concepts and tools that you will need to build fully functional UI-applications with the modern UI-building framework, Windows Presentation Foundation (WPF).

Teaching Approach

No fluff, no ranting, no beating the air. I esteem your time. The course material is succinct, yet comprehensive. All important concepts are covered. Particularly important topics are covered in-depth. For absolute beginners, I offer my help on Skype absolutely free, if requested.

Take this course and you will be satisfied.

Build a strong foundation in WPF with this course

Today, almost all applications have rich UI, console applications are very specific. Learning the essentials of WPF puts a powerful and very useful tool at your fingertips. Being familiar with WPF will make it absolutely easy to move to Universal Windows Platform (UWP) if needed because these technologies rely basically on the same principles and they are both XAML-based.

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Objects Equality in C#. Important Facts That You Should Know

Don’t forget that if you want to get my upcoming video courses with 50% discount, then fill the following  form.

C# provides many ways to compare objects, not only to compare class instances, but also structures. Actually, there are so many ways, that it requires to put them in order. All those possible options of comparing confuse people in case of misunderstanding them and their possible implementations.

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Cryptography in .NET for Beginners

This is a brief introduction into .NET cryptography.

Hashes

Hashing is a transformation process of some input data of an arbitrary length into an array of bytes of fixed size.
Hash is a one-side transformation function, the result of which cannot be reversed for receiving original input data. Very often it is used to store passwords. Even if an attacker gets a hash, he can’t retrieve the password from it. The length of a hash is determined by a hashing algorithm. In .NET you can find the following hashing algorithms (all of which derive from the HashAlgorithm base class):

  • MD5 — 128 bits in length
  • SHA (Secure Hash Algorithm) — there is no such a class, but there are SHA1 (160 bits), SHA256, SHA384, SHA512
  • KeydHashAlgorithm (also known as Message Authentication Code). Represented by the following classes of  algorithms: HMAC and MACTripleDES

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Money Type as Value Object, or Don’t Rely on Primitive Types!

Primitive Types Obsession Problem

Today I’m going to discuss the problem of using primitive types instead of abstractions. This problem was discussed in the blog of Mark Seemann. Read it, if you haven’t read it yet.
In this post I’m going to talk about Money type as an abstraction instead of using decimal type for representing money-values.
In the last project I’ve been participating in, we relied on a decimal and integer types for a long time. From the beginning, we knew that using primitive types for values of that kind is an anti-pattern, but we stubbornly have been using them. In the US there are cents and dollars. In the Russian Federation – rubles and kopeks. 1 ruble = 100 kopeks. Our system inter-operated with an external system which performed all its calculations in kopeks. So it required kopeks as the input and returned kopeks as the output. If we wanted to pass in 2rubles and 50kopeks, then we passed in Int32 amount = 250;

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What Every WPF-Developer Must Know? Learn Basic Concepts

These days I’m working on a video course about Microsoft WPF foundations. And today I want to address some basic notions that every UI-developer should be aware of and be able to explain them. That will become an entry point for my WPF tutorial. The notions I’m talking about are the following:

  • DPI (dots per inch), PPI (pixels per inch). What’s the difference?
  • Pixel
  • Raster Graphics and Vector Graphics
  • Independent Pixel
  • Aspect Ratio
  • ClearType rendering

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When Method Is Better Than Property?

That’s a well known question. Actually, I knew the difference between methods and properties long ago. Despite of that, recently I stumbled upon my own incorrect choice between those semantic constructions. That’s why I decided to write this post – in order to solidify the understanding of the difference between property and method.

Method vs Property fail in BCL

The most notorious fail of creating a property inside the BCL (FCL) in .NET instead of a method is the DateTime.Now property. In my opinion, this particular case is not the worst in history, though it’s an embarrassing one. So, what’s wrong with that the DateTime.Now is implemented as a property rather than a method? This isn’t wrong from the point of the actual implementation, it is implemented correctly, the point is that this is semantically wrong from the API design perspective. If every time the getter of a property returns different values, then this is a method, not a property. Why? Because a property is an attribute of an entity. For example, Year is an attribute of a Date, so it would be correct to get the year as it follows: DateTime.Now().Year. Yes, that’s it, that’s how it should look like, not like a chain wreck – DateTime.Now.Year. By the way, similar by the case Guid.NewGuid() member is implemented as a method. In this case, the word “New” dictates that this should be a method, but for example they could have named it Guid.Next and even in this case it should be a method, as well as the DateTime.Now!

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