WPF中依赖属性及附加属性的概念及用法

完全来源于十月的寒流，感谢大佬讲解

依赖属性

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由依赖属性提供的属性功能
与字段支持的属性不同，依赖属性扩展了属性的功能。通常，添加的功能表示或支持以下功能之一：

资源
数据绑定
样式
动画
元数据重写
属性值继承
WPF 设计器集成

    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            CustomTextBox customTextBox = new CustomTextBox();
            customTextBox.IsHightLighted = true;

            customTextBox.SetValue(CustomTextBox.IsHightLightedProperty, true);
        }
    }

    public class CustomTextBox : TextBox
    {
        public bool IsHightLighted
        {
            get { return (bool)GetValue(IsHightLightedProperty); }
            set { SetValue(IsHightLightedProperty, value); }
        }

        public static readonly DependencyProperty IsHightLightedProperty =
            DependencyProperty.Register("IsHightLighted", typeof(bool), typeof(CustomTextBox), new PropertyMetadata(false));
    }

#region HasText
public bool HasText => (bool)GetValue(HasTextProperty);

public static readonly DependencyProperty HasTextProperty;
public static readonly DependencyPropertyKey HasTextPropertyKey;

static CustomTextBox()
{
    HasTextPropertyKey = DependencyProperty.RegisterReadOnly(
        "HasText",
        typeof(bool),
        typeof(CustomTextBox),
        new PropertyMetadata(false)
        );
    HasTextProperty = HasTextPropertyKey.DependencyProperty;
}
#endregion

<Window x:Class="Test_05.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:Test_05"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">

    <Window.Resources>
        <Style TargetType="local:CustomTextBox">
            <Style.Triggers>
                <Trigger Property="IsHightLighted" Value="True">
                    <Setter Property="Background" Value="Yellow"></Setter>
                </Trigger>
                <Trigger Property="IsHightLighted" Value="False">
                    <Setter Property="Background" Value="Blue"></Setter>
                </Trigger>
            </Style.Triggers>
        </Style>
    </Window.Resources>
    <StackPanel>
        <local:CustomTextBox Text="Hello World!" FontSize="30" IsHightLighted="True"></local:CustomTextBox>
    </StackPanel>
</Window>

附加属性

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    <StackPanel>
        <!--<local:CustomTextBox Text="Hello World!" FontSize="30" IsHightLighted="True"></local:CustomTextBox>-->
        <local:CustomTextBox Text="Hello World!" FontSize="30">
            <local:CustomTextBox.IsHightLighted>
                true
            </local:CustomTextBox.IsHightLighted>
            <Grid.Row>1</Grid.Row>
        </local:CustomTextBox>
    </StackPanel>

<StackPanel>
    <local:CustomTextBox x:Name="aoteman" local:TextBoxHelper.Title="this is test" FontSize="30"
                         Text="{Binding RelativeSource={RelativeSource self}, Path=(local:TextBoxHelper.Title)}"></local:CustomTextBox>

    <!--<local:CustomTextBox x:Name="aoteman" FontSize="30"
                         Text="{Binding RelativeSource={RelativeSource self}, Path=(local:TextBoxHelper.Title)}"></local:CustomTextBox>-->
</StackPanel>

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
        //TextBoxHelper.SetTitle(aoteman, "this is aoteman");
    }
}

public class CustomTextBox : TextBox
{
    public bool IsHightLighted
    {
        get { return (bool)GetValue(IsHightLightedProperty); }
        set { SetValue(IsHightLightedProperty, value); }
    }

    public static readonly DependencyProperty IsHightLightedProperty =
        DependencyProperty.Register("IsHightLighted", typeof(bool), typeof(CustomTextBox), new PropertyMetadata(false));

    public bool HasText => (bool)GetValue(HasTextProperty);

    public static readonly DependencyProperty HasTextProperty;
    public static readonly DependencyPropertyKey HasTextPropertyKey;

    static CustomTextBox()
    {
        HasTextPropertyKey = DependencyProperty.RegisterReadOnly(
            "HasText",
            typeof(bool),
            typeof(CustomTextBox),
            new PropertyMetadata(false)
            );
        HasTextProperty = HasTextPropertyKey.DependencyProperty;
    }
}

public class TextBoxHelper
{
    public static string GetTitle(DependencyObject obj)
    {
        return (string)obj.GetValue(TitleProperty);
    }

    public static void SetTitle(DependencyObject obj, string value)
    {
        obj.SetValue(TitleProperty, value);
    }

    // Using a DependencyProperty as the backing store for Title.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty TitleProperty =
        DependencyProperty.RegisterAttached("Title", typeof(string), typeof(TextBoxHelper), new PropertyMetadata(""));
}

TextBox HasText实现一

<Window x:Class="Test_01.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:Test_01"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <Window.Resources>
    </Window.Resources>
    <StackPanel>
        <!--<local:CustomTextBox x:Name="aoteman" local:TextBoxHelper.Title="this is test" FontSize="30"
                             Text="{Binding RelativeSource={RelativeSource self}, Path=(local:TextBoxHelper.Title)}"></local:CustomTextBox>-->
        <TextBox x:Name="tBox" Text="1234" FontSize="30" local:TextBoxHelper.MonitorTextChange="True"></TextBox>
        <CheckBox IsChecked="{Binding ElementName=tBox, Path=(local:TextBoxHelper.HasText)}" FontSize="30"></CheckBox>
    </StackPanel>
</Window>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace Test_01
{
    /// <summary>
    /// MainWindow.xaml 的交互逻辑
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }
    }

    public class TextBoxHelper
    {
        public static bool GetHasText(DependencyObject obj)
        {
            return (bool)obj.GetValue(HasTextProperty);
        }

        public static void SetHasText(DependencyObject obj, bool value)
        {
            obj.SetValue(HasTextProperty, value);
        }

        public static readonly DependencyProperty HasTextProperty =
            DependencyProperty.RegisterAttached(
                "HasText",
                typeof(bool),
                typeof(TextBoxHelper),
                new PropertyMetadata(false)
            );

        public static bool GetMonitorTextChange(DependencyObject obj)
        {
            return (bool)obj.GetValue(MonitorTextChangeProperty);
        }

        public static void SetMonitorTextChange(DependencyObject obj, bool value)
        {
            obj.SetValue(MonitorTextChangeProperty, value);
        }

        // Using a DependencyProperty as the backing store for MonitorTextChange.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty MonitorTextChangeProperty =
            DependencyProperty.RegisterAttached(
                "MonitorTextChange",
                typeof(bool),
                typeof(TextBoxHelper),
                new PropertyMetadata(false, MonitorTextChangedPropertyChanged)
            );

        private static void MonitorTextChangedPropertyChanged(
            DependencyObject d,
            DependencyPropertyChangedEventArgs e
        )
        {
            if (d is TextBox box == false)
            {
                throw new NotSupportedException();
            }
            if ((bool)e.NewValue)
            {
                box.TextChanged += TextChanged;
                SetHasText(box, !string.IsNullOrEmpty(box.Text));
            }
            else
            {
                box.TextChanged -= TextChanged;
            }
        }

        private static void TextChanged(object sender, TextChangedEventArgs e)
        {
            var box = sender as TextBox;
            SetHasText(box, !string.IsNullOrEmpty(box.Text));
        }
    }
}

TextBox HasText只读实现二

<Window x:Class="Test_01.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:Test_01"
        mc:Ignorable="d" 
        Title="MainWindow" Height="450" Width="800">
    <Window.Resources>
    </Window.Resources>
    <StackPanel>
        <!--<local:CustomTextBox x:Name="aoteman" local:TextBoxHelper.Title="this is test" FontSize="30"
                             Text="{Binding RelativeSource={RelativeSource self}, Path=(local:TextBoxHelper.Title)}"></local:CustomTextBox>-->
        <TextBox x:Name="tBox" Text="1234" FontSize="30" local:TextBoxHelper.MonitorTextChange="True"></TextBox>
        <CheckBox IsChecked="{Binding ElementName=tBox, Path=(local:TextBoxHelper.HasText), Mode=OneWay}" FontSize="30"></CheckBox>
    </StackPanel>
</Window>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Security.Policy;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace Test_01
{
    /// <summary>
    /// MainWindow.xaml 的交互逻辑
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }
    }

    public class TextBoxHelper
    {
        static TextBoxHelper()
        {
            HasTextProperty = HasTextPropertyKey.DependencyProperty;
        }

        public static bool GetHasText(DependencyObject obj)
        {
            return (bool)obj.GetValue(HasTextProperty);
        }

        public static void SetHasText(DependencyObject obj, bool value)
        {
            obj.SetValue(HasTextPropertyKey, value);
        }

        public static readonly DependencyProperty HasTextProperty;

        public static readonly DependencyPropertyKey HasTextPropertyKey =
            DependencyProperty.RegisterAttachedReadOnly(
                "HasText",
                typeof(bool),
                typeof(TextBoxHelper),
                new PropertyMetadata(false)
            );

        public static bool GetMonitorTextChange(DependencyObject obj)
        {
            return (bool)obj.GetValue(MonitorTextChangeProperty);
        }

        public static void SetMonitorTextChange(DependencyObject obj, bool value)
        {
            obj.SetValue(MonitorTextChangeProperty, value);
        }

        public static readonly DependencyProperty MonitorTextChangeProperty =
            DependencyProperty.RegisterAttached(
                "MonitorTextChange",
                typeof(bool),
                typeof(TextBoxHelper),
                new PropertyMetadata(false, MonitorTextChangedPropertyChanged)
            );

        private static void MonitorTextChangedPropertyChanged(
            DependencyObject d,
            DependencyPropertyChangedEventArgs e
        )
        {
            if (d is TextBox box == false)
            {
                throw new NotSupportedException();
            }
            if ((bool)e.NewValue)
            {
                box.TextChanged += TextChanged;
                SetHasText(box, !string.IsNullOrEmpty(box.Text));
            }
            else
            {
                box.TextChanged -= TextChanged;
            }
        }

        private static void TextChanged(object sender, TextChangedEventArgs e)
        {
            var box = sender as TextBox;
            SetHasText(box, !string.IsNullOrEmpty(box.Text));
        }
    }
}

{Binding}解释

local:TextBoxHelper.MonitorTextChange="True"：这是自定义属性local:TextBoxHelper.MonitorTextChange的设置，是自定义控件或附加属性的一部分。这个属性被用来监测文本的变化。
<CheckBox IsChecked="{Binding ElementName=tBox, Path=(local:TextBoxHelper.HasText)}" FontSize="30">：这是一个复选框控件，其中包含了数据绑定。
- IsChecked="{Binding ...}"：这部分指示IsChecked属性将被绑定到某个数据源。
- ElementName=tBox：这是一个Binding的设置，指定了数据源是哪个控件，即名为"tBox"的TextBox控件。
- Path=(local:TextBoxHelper.HasText)：这是Binding的路径设置。告诉WPF应用程序查找名为"tBox"的控件，并在该控件上查找名为"HasText"的属性。这个属性用于确定TextBox中是否有文本。

关于这些概念的详细解释：

ElementName：这是一个Binding设置，用于指定绑定的数据源控件的名称。在示例中，数据源是名为"tBox"的TextBox。
Path：这是用于指定数据源控件上的属性或属性路径的设置。在这里，你正在查找名为"HasText"的属性，该属性被用于确定CheckBox的IsChecked属性。
(local:TextBoxHelper.HasText)：这种写法通常用于引用附加属性，其中local表示当前命名空间，TextBoxHelper是一个附加属性的名称，而HasText是这个附加属性的属性名。
这种绑定方式可以用于将一个控件的属性绑定到另一个控件的属性，使它们保持同步，例如，在文本框中输入文本时，相关的复选框的选中状态也会相应地改变。这种绑定通常用于实现界面元素之间的交互和数据同步。

e.NewValue解释
e.NewValue 是一个 DependencyPropertyChangedEventArgs 对象的属性，它用于存储关于依赖属性更改的信息。

含义：e.NewValue 表示在依赖属性更改时，属性的新值。当一个依赖属性的值发生变化时，e.NewValue 将包含新值，以便可以在事件处理程序中访问并使用它。
作用：e.NewValue 主要用于在属性更改事件处理程序中获取属性的新值。它允许在属性值发生变化时采取相应的操作。例如，可以根据新值来更新界面元素、执行计算或触发其他操作。
类型：e.NewValue 的类型取决于被监测属性的类型。它是一个 object 类型，因为它需要能够表示任何类型的值。通常，需要将其转换为适当的类型，以便在代码中使用。这个类型转换通常是基于知道将要更改的属性的类型。例如，在上述代码示例中，似乎假定属性的新值是一个布尔值。

在提供的代码示例中，if ((bool)e.NewValue) 的作用是检查某个依赖属性的新值是否为 true，以决定是否执行特定的操作。这是一个典型的用例，其中 e.NewValue 用于确定如何响应属性的更改。