[RS3：1709] Fall Creator的更新：ColorPicker.Color不能以两种方式绑定到DependencyProperty

问题描述

如果你有一个ColorIicker，其Color使用{x：Bind}和模式TwoWay绑定到一个支持DependencyProperty，你会得到一个StackOverflowException。

If you have a ColorPicker whose Color is bound using {x:Bind} and mode TwoWay to a backing DependencyProperty, you get a StackOverflowException.

这将是一个相当常见的场景，有人想将ColorPicker的Color绑定到'支持'DependencyProperty，可能是在Page或ContentDialog中。

This is going to be a fairly common scenario, where someone wants to bind the ColorPicker's Color to a 'backing' DependencyProperty, perhaps in a Page or a ContentDialog.

问题是Color类型的DependencyProperty显然没有我不知道如何比较两种颜色，即使（至少在C＃中），如果两个Color实例具有相同的A，R，G和B值，则以下所有都返回true：

The problem is that a DependencyProperty of type Color apparently doesn't know how to compare two Colors, even though (in C#, at least), if two Color instances have the same A, R, G and B values, all of the following return true:

color1 == color2
color1.Equals(color2)
Object.Equals(color1, color2)

另一方面，如果在包含的类上实现INotifyPropertyChanged并使用简单的CLR属性作为"支持"颜色，如下所示：

If, on the other hand, you implement INotifyPropertyChanged on your containing class and use a simple CLR property for the 'backing' color, like this:

public Color SelectedColor
{
    get { return m_selectedColor; }

    set
    {
        if (m_selectedColor != value)
        {
            m_selectedColor = value;
            OnPropertyChanged(nameof(SelectedColor));
        }
    }
}

然后它运作正常。

then it works just fine.

推荐答案

using System;

using Windows.UI;
using Windows.UI.Xaml;

namespace ColorPickerBug
{
	public class BadColorDP : DependencyObject
	{
		public BadColorDP()
		{
			// This is NOT a change from the DP's default value, but it will display
			// 'OnMyColorPropertyChanged' in the Debug window.
			MyColor = Colors.Red;

			// So will these (the first one correctly, the second on incorrectly).
			MyColor = Colors.Yellow;
			MyColor = Colors.Yellow;
		}

		public Color MyColor
		{
			get { return (Color)GetValue(MyColorProperty); }
			set { SetValue(MyColorProperty, value); }
		}

		private static void OnMyColorPropertyChanged(DependencyObject dobj, DependencyPropertyChangedEventArgs args)
		{
			System.Diagnostics.Debug.WriteLine("OnMyColorPropertyChanged");
		}

		public static readonly DependencyProperty MyColorProperty =
			DependencyProperty.Register("MyColor",
										typeof(Color),
										typeof(BadColorDP),
										new PropertyMetadata(Colors.Red, OnMyColorPropertyChanged));
	}
}

这是导致TwoWay绑定在控件和DP之间来回"反弹"的原因 - DP认为每个 b 每次更改都值得通知，即使这不是"真正的"更改。

This is what causes the TwoWay binding to 'bounce' back and forth between the control and the DP -- the DP thinks thatevery change is worthy of notification, even if it's not a 'real' change.

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