c# - WPF 中的基类 DependencyProperty 值更改

Question

我在 ClassA 中有一个 DependencyProperty。我从 ClassA 派生了另一个 ClassB。在 ClassA 中更新或更改此属性的值时，如何在派生的 ClassB 中通知或反映它而不在 ClassA 中添加任何其他代码？

Answer 1

通过派生类中的DependencyProperty.OverrideMetadata为 ClassB 注册 PropertyChangedCallback：

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

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

Answer 2

如果您希望在两个类中引发属性更改，您可以添加另一个所有者。

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

只是评论：如果您使用 B 类的 2 个实例，则会出现错误

• _innerException {“PropertyMetadata 已经为类型 'ClassB' 注册。”} System.Exception {System.ArgumentException}

Answer 4

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";
    }
}