Base class DependencyProperty value change in WPF

Question

I have a DependencyProperty in the ClassA. I derived another ClassB from ClassA. When the value of this property is updated or changed in ClassA, How it can be notified or reflected in the derived ClassB with out adding any additional code in ClassA ?

Answer 1

By registering a PropertyChangedCallback for ClassB through DependencyProperty.OverrideMetadata in the derived class:

class ClassB
{
    static ClassB()
    {
        ClassA.SomeValueProperty.OverrideMetadata(
            typeof(ClassB), new PropertyMetadata(SomeValuePropertyChanged);
    }

    private static SomeValuePropertyChanged(
        DependencyObject o, DependencyPropertyChangedArgs e)
    {
        ...
    }
}

Answer 2

If you want the property change to be raised in both classes you can add another owner.

using System.Windows;

namespace dp
{
    public class ClassA : DependencyObject
    {
        public string TestProperty
        {
            get { return (string)GetValue(TestPropertyProperty); }
            set { SetValue(TestPropertyProperty, value); }
        }
        public static readonly DependencyProperty TestPropertyProperty =
            DependencyProperty.Register("TestProperty", typeof(string), typeof(ClassA), new PropertyMetadata(null, new PropertyChangedCallback( (s, e)=>
                {
                })));
    }

    public class ClassB : ClassA
    {
        static ClassB()
        {
            TestPropertyProperty.AddOwner(typeof(ClassB), new PropertyMetadata((s, e) =>
                {
                }));
        }    
    }

    public partial class MainWindow : Window
    {
        public ClassB TestClassB
        {
            get { return (ClassB)GetValue(TestClassBProperty); }
            set { SetValue(TestClassBProperty, value); }
        }        
        public static readonly DependencyProperty TestClassBProperty =
            DependencyProperty.Register("TestClassB", typeof(ClassB), typeof(MainWindow), new PropertyMetadata(null));


        public MainWindow()
        {
            InitializeComponent();
            TestClassB = new ClassB();
            TestClassB.TestProperty = "test";
        }
    }
}

Answer 3

public class ClassA : DependencyObject
{
    /// <summary>
    /// 
    /// </summary>
    public string PropertyA
    {
        get { return (string)GetValue(PropertyAProperty); }
        set { SetValue(PropertyAProperty, value); }
    }

    /// <summary>
    /// Identifies the <see cref="PropertyA"/> dependency property.
    /// </summary>
    public static readonly DependencyProperty PropertyAProperty =
    DependencyProperty.Register("PropertyA", typeof(string), typeof(ClassA), new PropertyMetadata("A"));
}


public class ClassB : ClassA
{
    /// <summary>
    /// 
    /// </summary>
    public string PropertyB
    {
        get { return (string)GetValue(PropertyBProperty); }
        set { SetValue(PropertyBProperty, value); }
    }

    /// <summary>
    /// Identifies the <see cref="PropertyB"/> dependency property.
    /// </summary>
    public static readonly DependencyProperty PropertyBProperty =
    DependencyProperty.Register("PropertyB", typeof(string), typeof(ClassA), new PropertyMetadata("B"));

    public ClassB()
    {
        ClassA.PropertyAProperty.OverrideMetadata(typeof(ClassB), new PropertyMetadata(AValuePropertyChanged));
    }

    private static void AValuePropertyChanged(DependencyObject o, DependencyPropertyChangedEventArgs e)
    {
        MessageBox.Show(e.NewValue.ToString());
    }
}

public partial class MainWindow4 : Window
{
    /// <summary>
    /// 
    /// </summary>
    public MainWindow4()
    {
        InitializeComponent();

        this.Reference = new ClassB();
    }

    private ClassB Reference { get; set; }

    /// <summary>
    /// 
    /// </summary>
    /// <param name="sender"></param>
    /// <param name="e"></param>
    private void Button_Click(object sender, RoutedEventArgs e)
    {



        this.Reference.PropertyA = "hello";
    }
}