Friday, September 11, 2009

Is code coverage usefull for measuring software quality?

There is a lot of debate going on how much percentage should be attained. But first however is code coverage a good measurement or quality? In my personal opinion it is very usefull if an historical trend is kept. if coverage drops over time this migt be an indicator of issues tha are arising somewhere else... not enough time, quick and dirty hacks,...

But how much is enough? this like almost everything in software development is offcourse it depends. I think it largely depends on the type of application you are building, if it is ver largely dependant on workflows and long running processes the significance is going to be less then when you are doing a lot of calculations. And offcourse code coverage does not cover 1 thing which is quite important and usually the root of all evil: missing requirements :)

Monday, September 07, 2009

Implementing INotifyPropertyChanged by using Unity Interception

This example uses Unity interception to be able to bind objects to a UI by just applying a [Notify] attribute to a property, this done by intercepting the call and propagating it to a INotifyPropertyChanged implementation.
From MSDN:
The INotifyPropertyChanged interface is used to notify clients, typically binding clients, that a property value has changed.

Step 1 create an abstract class that encapsulates all the functionality we need.
See below for a class diagram:

Step 2 create the handler:
NotifyPropertyChangedHandler which inherits from ICallHandler
public IMethodReturn Invoke(IMethodInvocation input, GetNextHandlerDelegate getNext) {

IMethodReturn result = getNext()(input, getNext);

if (!input.MethodBase.Name.StartsWith("set_")) return result;
//Remov the set_ to get the property's name
var propertyName = input.MethodBase.Name.Remove(0, 4);
//invoke the modified property
//maybe we should check if the target is indeed o BindableOjectBase ;)
BindableObjectBase target = (BindableObjectBase)input.Target;
return result;

Step 3: Create the attribute
Create a NotifyPropertyChangedAttribute class which inherits from HandlerAttribute
create a default constructor:
public NotifyPropertyChangedAttribute() {
_CallHandler = new NotifyPropertyChangedHandler();

override the folowing method
public override ICallHandler CreateHandler(IUnityContainer container) {
return _CallHandler;
Step 4: Setting up the UnityContainer:
UnityContainer_Container = new UnityContainer();
//Registring interception extension
_Container.Configure().SetDefaultInterceptorFor(new TransparentProxyInterceptor());
var object container.Resolve();

the last step took a little time to get it working the way I wanted since DI usually works by injecting interface implementations but this was not what I wanted to do. Since interfaces define behaviour and properties have nothing to do with behaviour but with state.

I will post the full source code later