Coupling and cohesion

I was reading ploeh's blog this morning and it made me think about coupling and cohesion in general. These are import concepts in software development, Wikipedia has great definitions for both here & here. These are often contrasted together but they are different concepts and just because you have low coupling doesn't mean you'll have high cohesion.

Using a car analogy the headlight unit for my Audi has tight (high) coupling because it's designed only to be fitted to a particular version. You could say it has high cohesion because it is part of a greater system to show light when a button is turned\clicked....

Taking another part of the car the tyre, the actual type of tyre will have low coupling to my Audi because it would suitable for several different models and makes, it would also have low coupling to the wheel, it has to fit a particular size but it could fit many wheels of this size. The tyre would still have high cohesion for the same reason, part of a greater system to make a car move...

The box in the boot (trunk) of the car has low cohesion because it contains all the stuff I drive round with, not just stuff such as oil, glass cleaner, foot pump etc. but stuff I have just left in the car overtime. There only relation is they are all in the same box.

What I find interesting about measures of coupling, is there related cost: the higher the coupling the more likely there will be few options available to replace\maintain which means higher costs, where as low coupling allows for multiple solutions and therefore more likely reduced costs.

Comments

Integrating jasmine into Visual Studio 2010/2011 beta

Following on from my previous post about testing javascript with jasmine. I was interested to explore integration into visual studio 2010 so I could run them along side test written in another language like C#. I found the VS 2010 extension Chutpah (pronounced 'hutz-pah'). This got me up and running with the ability to run test manually and to my surprised it worked by only have the SpecRunner.html file open. I didn't a csproj or sln file containing the javascript, it's clever enough to resolve all dependencies: Test results are render in the output window of VS 2010: This is good and I appreciate the work someone has done to get this far but I want more... I want integration into Resharper... A quick squizz on the inter'webs and I end posting a request on jetBrains forum , it looks like support is coming in R# 7. Then I thought lets check out the current beta and see, so off I go and boot Win8 and install R#7 beta and see if it's there yet... ...

Implementing a busy indicator using a visual overlay in MVVM

This is a technique we use at work to lock the UI whilst some long running process is happening - preventing the user clicking on stuff whilst it's retrieving or rendering data. Now we could have done this by launching a child dialog window but that feels rather out of date and clumsy, we wanted a more modern pattern similar to the way <div> overlays are done on the web. Imagine we have the following simple WPF app and when 'Click' is pressed a busy waiting overlay is shown for the duration entered into the text box. What I'm interested in here is not the actual UI element of the busy indicator but how I go about getting this to show & hide from when using MVVM. The actual UI elements are the standard Busy Indicator coming from the WPF Toolkit : The XAML behind this window is very simple, the important part is the ViewHost. As you can see the ViewHost uses a ContentPresenter element which is bound to the view model, IMainViewModel, it contains 3 child v...

Showing a message box from a ViewModel in MVVM

I was doing a code review with a client last week for a WPF app using MVVM and they asked ' How can I show a message from the ViewModel? '. What follows is how I would (and have) solved the problem in the past. When I hear the words ' show a message... ' I instantly think you mean show a transient modal message box that requires the user input before continuing ' with something else ' - once the user has interacted with the message box it will disappear. The following solution only applies to this scenario. The first solution is the easiest but is very wrong from a separation perspective. It violates the ideas behind the Model-View-Controller pattern because it places View concerns inside the ViewModel - the ViewModel now knows about the type of the View and specifically it knows how to show a message box window: The second approach addresses this concern by introducing the idea of messaging\events between the ViewModel and the View. In the example ...

Awkward Coder

Search This Blog