How To Raise Property Changed events on a Dependency Property?

Question

OK, so I have this control with two properties. One of these is a DependencyProperty, the other is an "alias" to the first one. What I need to be able to do is raise the PropertyChanged event for the second one (the alias) when the first one is changed.

NOTE: I am using DependencyObjects, not INotifyPropertyChanged (tried that, didn't work because my control is a sub-classed ListView)

something like this.....

protected override void OnPropertyChanged(DependencyPropertyChangedEventArgs e)
{
    base.OnPropertyChanged(e);
    if (e.Property == MyFirstProperty)
    {
        RaiseAnEvent( MySecondProperty ); /// what is the code that would go here?
    }    
}

If I were using an INotify I could do like this...

public string SecondProperty
{
    get
    {
        return this.m_IconPath;
    }
}

public string IconPath
{
    get
    {
        return this.m_IconPath;
    }
    set
    {
        if (this.m_IconPath != value)
        {
            this.m_IconPath = value;
        this.SendPropertyChanged("IconPath");
        this.SendPropertyChanged("SecondProperty");
        }
    }
}

where I can raise PropertyChanged events on multiple properties from one setter. I need to be able to do the same thing, only using DependencyProperties.

Answer 1

I question the logic of raising a PropertyChanged event on the second property when it's the first property that's changing. If the second properties value changes then the PropertyChanged event could be raised there.

At any rate, the answer to your question is you should implement INotifyPropertyChange. This interface contains the PropertyChanged event. Implementing INotifyPropertyChanged lets other code know that the class has the PropertyChanged event, so that code can hook up a handler. After implementing INotifyPropertyChange, the code that goes in the if statement of your OnPropertyChanged is:

if (PropertyChanged != null)
    PropertyChanged(new PropertyChangedEventArgs("MySecondProperty"));

Answer 2

1. Implement INotifyPropertyChanged in your class.

2. Specify a callback in the property metadata when you register the dependency property.

3. In the callback, raise the PropertyChanged event.

Adding the callback:

public static DependencyProperty FirstProperty = DependencyProperty.Register(
  "First", 
  typeof(string), 
  typeof(MyType),
  new FrameworkPropertyMetadata(
     false, 
     new PropertyChangedCallback(OnFirstPropertyChanged)));

Raising PropertyChanged in the callback:

private static void OnFirstPropertyChanged(
   DependencyObject sender, DependencyPropertyChangedEventArgs e)
{
   PropertyChangedEventHandler h = PropertyChanged;
   if (h != null)
   {
      h(sender, new PropertyChangedEventArgs("Second"));
   }
}