依赖附加属性的定义
基本过程：声明、注册、包装
依赖附加属性必须在依赖对象，附加属性不一定，关注的是被附加的对象是否是依赖对象
快捷方式：propa + tab
关键字：RegisterAttached
// 方法封装
public static int GetIndex(DependencyObject obj)
{return (int)obj.GetValue(IndexProperty);
}public static void SetIndex(DependencyObject obj, int value)
{obj.SetValue(IndexProperty, value);
}// 声明与注册
public static readonly DependencyProperty IndexProperty =DependencyProperty.RegisterAttached("Index", typeof(int), typeof(XHPanel), new PropertyMetadata(-1));依赖附加属性的意义和作用
1. 用来辅助布局（布局控件与子控件的关系）
一般容器控件提供给子控件使用的，如果Grid.Row
使用方式：在容器控件中检查每个子项，从子项中获取附加属性的值 容器对象调用对应的GetValue方法，传入给被附加对象
a. 自定义控件的附加属性
父亲的属性：
// 方法封装
public static int GetIndex(DependencyObject obj)
{return (int)obj.GetValue(IndexProperty);
}public static void SetIndex(DependencyObject obj, int value)
{obj.SetValue(IndexProperty, value);
}// 声明与注册
public static readonly DependencyProperty IndexProperty =DependencyProperty.RegisterAttached("Index", typeof(int), typeof(XHPanel), new PropertyMetadata(-1));使用方法：
可以在子控件中都使用Index属性
<local:XHPanel Test="12" ColumnSpace="20" RowSpace="20" Visibility="Collapsed"><Border Height="100" Background="Red" local:XHPanel.Index="1" /><Border Height="100" Background="Orange" local:XHPanel.Index="2" /><Border Height="100" Background="Yellow" local:XHPanel.Index="3"/><Border Height="100" Background="Green" local:XHPanel.Index="4"/><Border Height="100" Background="LightGreen" local:XHPanel.Index="5"/><Border Height="100" Background="Blue" local:XHPanel.Index="6"/><local:DependencyPropertyStudy local:XHPanel.Index="7" x:Name="dps" Background="Purple" Height="100"/>
</local:XHPanel>在执行布局的时候，可以获取每个子控件的Index，进行不一样的布局：
获取部分的核心代码：
protected override Size ArrangeOverride(Size finalSize)
{for (int i = 1; i < newElements.Count+1; i++){var index = GetIndex(item); // 获取对应对象的Index 附加属性值}// 根据index的不一样，进行不一样的布局.....return base.ArrangeOverride(finalSize);
}2. 用来扩展绑定属性（单独应对对象功能）
一般对接特定对象，比如PasswordBox
使用方法：定义一个类，在类定义相关附加属性，利用这些附加属性进行数据与控件属性的转接
需求：PasswordBox中的password属性不可以绑定，不是依赖属性，但是我这边又需要动态赋值，所以，此时需要写个扩展属性:
核心代码如下：
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;namespace XH.PropertyLesson
{public class PWHelper{public static string GetPassword(DependencyObject obj){return (string)obj.GetValue(PasswordProperty);}/// <summary>/// 设置Password/// </summary>/// <param name="obj">所附加的对象</param>/// <param name="value"></param>public static void SetPassword(DependencyObject obj, string value){obj.SetValue(PasswordProperty, value);}// Using a DependencyProperty as the backing store for Password. This enables animation, styling, binding, etc...public static readonly DependencyProperty PasswordProperty =DependencyProperty.RegisterAttached("Password", typeof(string), typeof(PWHelper), new PropertyMetadata("",new PropertyChangedCallback(OnPasswordChanged)));// 1、可以获取到对应的控件 PasswordBox// 2、关联两个方向// - 从绑定到控件// - 从控件到绑定（针对拿到的控件进行PasswordChanged事件的绑定）/// <summary>/// Password修改回调函数/// </summary>/// <param name="DependencyObject">实际附加的对象</param>/// <param name="e"></param>/// <exception cref="NotImplementedException"></exception>private static void OnPasswordChanged(DependencyObject d, DependencyPropertyChangedEventArgs e){var control = (d as PasswordBox);if (control == null) return;control.Password = e.NewValue as string;}private static void Control_PasswordChanged(object sender, RoutedEventArgs e){SetPassword((DependencyObject)sender, (sender as PasswordBox).Password);}public static object GetAttached(DependencyObject obj){return (object)obj.GetValue(AttachedProperty);}public static void SetAttached(DependencyObject obj, object value){obj.SetValue(AttachedProperty, value);}// 挂载事件public static readonly DependencyProperty AttachedProperty =DependencyProperty.RegisterAttached("Attached", typeof(object), typeof(PWHelper), new PropertyMetadata(null,new PropertyChangedCallback(OnAttachedChanged)));private static void OnAttachedChanged(DependencyObject d, DependencyPropertyChangedEventArgs e){var control = (d as PasswordBox);if (control == null) return;// 防止多次附加事件 可以先减 后加control.PasswordChanged -= Control_PasswordChanged; control.PasswordChanged += Control_PasswordChanged; }}
}
xaml使用代码：
<PasswordBox PasswordChar="*" Height="30" Width="100" local:PWHelper.Password="{Binding }"local:PWHelper.Attached="1"/>使用：
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