Changing DependencyProperty Base Class in WPF

Question

I have a DependencyProperty in ClassA. I got another ClassB from ClassA. When the value of this property is updated or changed in ClassA, how can it be notified or reflected in a derived ClassB without adding additional code to ClassA?

Answer 1

By registering PropertyChangedCallback for ClassB through DependencyProperty.OverrideMetadata in a 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
    {
        public 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";
    }
}