为什么要再次设置此Animatable属性？

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问题描述

关注问题。

显然，出于某种原因，在显式设置了 Parent.Child 属性（在构造函数内部或在构造函数外部）后，），当我设置 Parent.Child 对象的 Child.Trigger 属性时， Parent.Child 对象再次被设置。这可以通过中断静态构造函数中定义的 _OnChildChanged 方法来观察。在第二次调用它时，您可以看到 e.OldValue 不为null，并且与 e.NewValue 。

Apparently, for some reason after having explicitly set the Parent.Child property ( either inside the constructor or explicitly outside of the constructor ), when I set the Child.Trigger property of the Parent.Child object, the Parent.Child object is being set yet again. This can be observed by breaking on the _OnChildChanged method defined within the static constructor. On the second instance of it being called, you can see that e.OldValue is not null, and that it is the same as e.NewValue.

为什么是父级的 Child 属性 Trigger 属性时是否再次设置code>？

WHY is the Child property of Parent being set yet again when setting the Trigger property?

要符合必要的最低要求，：

In compliance with the requisite Minimal, Complete and Verifiable Example:

using System;
using System.Collections.Generic;
using System.Windows;
using System.Windows.Media.Animation;

namespace MCVE {
    /// <summary>
    /// Interaction logic for App.xaml
    /// </summary>
    public partial class Program {
        [STAThread]
        public static int Main( ) {
            Parent p = new Parent( );
            p.Child.Trigger = new object( );
            return 0;
        }
    }

    public abstract class Base : Animatable {
        public static readonly DependencyProperty TriggerProperty;
        static Base( ) =>
            TriggerProperty = DependencyProperty.Register(
                "Trigger", typeof( object ), typeof( Base) );
        public object Trigger {
            get => this.GetValue( TriggerProperty );
            set => this.SetValue( TriggerProperty, value );
        }
    }
    public class Parent : Base {
        public static readonly DependencyProperty ChildProperty;

        static Parent( ) {
            ChildProperty = DependencyProperty.Register(
                "Child", typeof( Child ), typeof( Parent ),
                new PropertyMetadata( null as Child, _OnChildChanged ) );

            void _OnChildChanged(
                DependencyObject sender,
                DependencyPropertyChangedEventArgs e ) =>
                Console.WriteLine( "Child Changed!" );
        }

        public Parent( ) : base( ) =>
            this.Child = new Child( );


        public Child Child {
            get => this.GetValue( ChildProperty ) as Child;
            set => this.SetValue( ChildProperty, value );
        }

        protected override Freezable CreateInstanceCore( ) => new Parent( );
    }
    public class Child : Base {
        public Child( ) : base( ) { }
        protected override Freezable CreateInstanceCore( ) => new Child( );
    }
}

要重现：

创建WPF项目。目标.Net 4.7.2。

选择 App.xaml

<$ c以下$ c>属性，将构建操作更改为页面

将代码粘贴到 App.xaml.cs 中。覆盖所有内容。

Create WPF Project. Target .Net 4.7.2.
Select App.xaml
Under Properties, change Build Action to Page
Paste code into App.xaml.cs. Overwrite EVERYTHING.

freezable

为什么要再次设置此Animatable属性？

问题描述

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