Monday, August 11, 2014

What about Catel.Fody and computed read-only properties change notifications?


On my last post I covered an implementation of INotifyPropertyChanged interface when using SheepAspect as AOP library. At the end, I also implemented an approach to notify changes of computed read-only properties. This approach has a down side, the dependent properties discovering process must be done in run-time.

Such journey recall us that Catel.Fody didn’t have support for notify property changes of computed read-only properties. How could such thing ever be possible? Obvious, “the shoemaker's son always goes barefoot” ;). But don’t worry: the feature is here, moving the dependent properties discovering process to build-time, thanks to Fody.

As you probably know by now, Catel.Fody will rewrite all properties on the DataObjectBase and ViewModelBase. So, if a property is written as this:

public string FirstName { get; set; }

will be weaved into

public string FirstName
{
    get { return GetValue<string>(FirstNameProperty); }
    set { SetValue(FirstNameProperty, value); }
}

public static readonly PropertyData FirstNameProperty = RegisterProperty("FirstName", typeof(string));


But now we added a new feature to Catel.Fody. If a read-only computed property like this one exists:

public string FullName
{
    get { return string.Format("{0} {1}", FirstName, LastName).Trim(); }
}

the OnPropertyChanged method will be also weaved into

protected override void OnPropertyChanged(AdvancedPropertyChangedEventArgs e)
{
    base.OnPropertyChanged(e);
    if (e.PropertyName.Equals("FirstName"))
    {
        base.RaisePropertyChanged("FullName");
    }
    if (e.PropertyName.Equals("LastName"))
    {
        base.RaisePropertyChanged("FullName");
    }
}


This feature is already available in the latest beta package of Catel.Fody.

Try yourself and let us know.

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