WPF custom DependencyProperty notify changes

wpf dependency-properties notify dependencyobject
morsanu picture morsanu · May 18, 2010 · Viewed 9.1k times · Source

I have a class called MyComponent and it has a DependencyProperty caled BackgroundProperty.

public class MyComponent
{
    public MyBackground Background
    {
        get { return (MyBackground)GetValue(BackgroundProperty); }
        set { SetValue(BackgroundProperty, value); }
    }
    public static readonly DependencyProperty BackgroundProperty =
        DependencyProperty.Register("Background", typeof(MyBackground),
            typeof(MyComponent), new FrameworkPropertyMetadata(default(MyBackground), new PropertyChangedCallback(OnPropertyChanged)));
}

MyBackground is a class that derives from DependencyObject and it has some DependencyProperties. 

public class MyBackground : DependencyObject
{
    public Color BaseColor
    {
        set { SetValue(BaseColorProperty, value); }
        get { return (Color)GetValue(BaseColorProperty); }
    }
    public static readonly DependencyProperty BaseColorProperty =
        DependencyProperty.Register("BaseColor", typeof(Color),
            typeof(MyBackground ), new UIPropertyMetadata(Colors.White));

    [...]
}

Now, what I want is when a property from MyBackground is changed, MyComponent to be notified that MyBackground has changed and the PropertyChangedCallback named OnPropertyChanged to be called.

Answer

kcnygaard picture kcnygaard · Oct 14, 2013

Bear with me for a second because it appears that you are trying to go against the grain of WPF. Since it seems you are writing code related to display logic, the typical method for getting related DependencyObjects to interact with one another is through bindings.

If, for example, MyComponent is a control of some sort and it uses the Background property in its ControlTemplate, you would use a TemplateBinding that references the Background property and any important sub-properties.

Since 1) you probably already know that and 2) you either aren't using templates or don't have them available, you can set up a binding in code in order to react to changes in to the Background property. If you provide more detail about what your OnPropertyChanged method does I can provide some sample code.

Related questions

INotifyPropertyChanged vs. DependencyProperty in ViewModel

When implementing the ViewModel in a Model-View-ViewModel architecture WPF application there seem to be two major choices how to make it databindable. I have seen implementations that use DependencyProperty for properties the View is going to bind against and I …

Read More
A 'Binding' can only be set on a DependencyProperty of a DependencyObject

From a custom control based on TextBox, I created a property named Items, in this way: public class NewTextBox : TextBox { public ItemCollection Items { get; set; } } When using the custom control in XAML, I cannot bind the property because it raises …

Read More
Listen to changes of dependency property

Is there any way to listen to changes of a DependencyProperty? I want to be notified and perform some actions when the value changes but I cannot use binding. It is a DependencyProperty of another class.

Read More