装饰器是wpf中可以浮在控件上面的一种组件，我们通常可以用来实现一些诸如控件拖动点、提示框、自定义鼠标等界面功能。装饰器的用法其实还是比较复杂的，几乎需要完全再cs中编写所有代码，对于样式要求较高的情况下，完全在cs中些控件的样式是比较困难的。为了改变这种状况，我们可以使用附加属性将装饰器的逻辑封装，提供一个可以在界面上定义的属性。
由于Adorner是一个抽象类不能直接实现，所有我们需要定义一个子类实现并它。
class NormalAdorner : Adorner
{
/// <summary>
/// 构造方法
/// </summary>
/// <param name="adornedElement">被添加装饰器的元素</param>
/// <param name="child">放到装饰器中的元素</param>
public NormalAdorner(UIElement adornedElement, UIElement child) : base(adornedElement);
protected override Visual GetVisualChild(int index);
protected override int VisualChildrenCount;
protected override Size ArrangeOverride(Size finalSize);
}
通过propa快捷定义一个名称为AdornerContent的附加属性其类型UIElement。
public static UIElementGetAdornerContent(DependencyObject obj)
{
return (UIElement)obj.GetValue(AdornerContent);
}
public static void SetAdornerContent(DependencyObject obj, Control value)
{
obj.SetValue(AdornerContent, value);
}
// Using a DependencyProperty as the backing store for MyProperty. This enables animation, styling, binding, etc...
public static readonly DependencyProperty AdornerContent =
DependencyProperty.RegisterAttached("AdornerContent", typeof(UIElement), typeof(AdornerHelper), new PropertyMetadata(null));
在附加属性改变事件中，进行装饰层的添加。
public void PropertyChangedCallback(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
var c = d as UIElement;
//获取装饰层
var layer = AdornerLayer.GetAdornerLayer(c);
//添加装饰器
layer.Add(new NormalAdorner(c, (UIElement)e.NewValue));
}
AdornerHelper.cs
using System;
using System.Windows;
using System.Windows.Documents;
using System.Windows.Media;
namespace AC
{
internal class AdornerHelper
{
public static UIElement GetAdornerContent(DependencyObject obj)
{
return (UIElement)obj.GetValue(AdornerContent);
}
public static void SetAdornerContent(DependencyObject obj, UIElement value)
{
obj.SetValue(AdornerContent, value);
}
// Using a DependencyProperty as the backing store for MyProperty. This enables animation, styling, binding, etc...
public static readonly DependencyProperty AdornerContent =
DependencyProperty.RegisterAttached("AdornerContent", typeof(UIElement), typeof(AdornerHelper), new PropertyMetadata(null, (d, e) =>
{
var c = d as FrameworkElement;
if (c == null)
return;
var adronerContent = e.NewValue as UIElement;
if (!c.IsLoaded)
{
if (adronerContent != null)
{
RoutedEventHandler l = null;
l = (s, E) =>
{
var content = GetAdornerContent(c);
if (content != null)
{
var layer = AdornerLayer.GetAdornerLayer(c);
if (layer == null)
throw new Exception("获取控件装饰层失败，控件可能没有装饰层！");
layer.Add(new NormalAdorner((UIElement)c, (UIElement)e.NewValue));
}
c.Loaded -= l;
};
c.Loaded += l;
}
}
else
{
var layer = AdornerLayer.GetAdornerLayer(d as Visual);
if (layer == null)
throw new Exception("获取控件装饰层失败，控件可能没有装饰层！");
if (e.OldValue != null)
{
var adorners = layer.GetAdorners(c);
foreach (var i in adorners)
{
if (i is NormalAdorner)
{
var na = i as NormalAdorner;
if (na.Child == e.OldValue)
{
layer.Remove(i);
break;
}
}
}
}
if (adronerContent != null)
{
layer.Add(new NormalAdorner((UIElement)c, (UIElement)e.NewValue));
}
}
}));
class NormalAdorner : Adorner
{
UIElement _child;
/// <summary>
/// 构造方法
/// </summary>
/// <param name="adornedElement">被添加装饰器的元素</param>
/// <param name="child">放到装饰器中的元素</param>
public NormalAdorner(UIElement adornedElement, UIElement child) : base(adornedElement)
{
_child = child;
AddVisualChild(child);
}
public UIElement Child { get { return _child; } }
protected override Visual GetVisualChild(int index)
{
return _child;
}
protected override int VisualChildrenCount
{
get
{
return 1;
}
}
protected override Size ArrangeOverride(Size finalSize)
{
_child.Arrange(new Rect(new Point(0, 0), finalSize));
return finalSize;
}
}
}
}
<Window x:Class="WpfApp2.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:WpfApp2"
xmlns:ac="clr-namespace:AC"
mc:Ignorable="d"
Title="MainWindow" Height="450" Width="800"
>
<Grid>
<Border Background="RoyalBlue" Width="320" Height="180" CornerRadius="10">
<!--添加装饰器-->
<ac:AdornerHelper.AdornerContent>
<Grid >
<Grid.Resources>
<Style TargetType="Thumb">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="Thumb">
<Border BorderBrush="Gray" BorderThickness="2" CornerRadius="8" Background="White"></Border>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</Grid.Resources>
<!--左-->
<Thumb Margin="-8,0,0,0" Width="16" Height="16" HorizontalAlignment="Left" VerticalAlignment="Center" Cursor="SizeWE"/>
<!--上-->
<Thumb Margin="0,-8,0,0" Width="16" Height="16" HorizontalAlignment="Center" VerticalAlignment="Top" Cursor="SizeNS"/>
<!--右-->
<Thumb Margin="0,0,-8,0" Width="16" Height="16" HorizontalAlignment="Right" VerticalAlignment="Center" Cursor="SizeWE"/>
<!--下-->
<Thumb Margin="0,0,0,-8" Width="16" Height="16" HorizontalAlignment="Center" VerticalAlignment="Bottom" Cursor="SizeNS"/>
<!--左上-->
<Thumb Margin="-8,-8,0,0" Width="16" Height="16" HorizontalAlignment="Left" VerticalAlignment="Top" Cursor="SizeNWSE"/>
<!--右上-->
<Thumb Margin="0,-8,-8,0" Width="16" Height="16" HorizontalAlignment="Right" VerticalAlignment="Top" Cursor="SizeNESW"/>
<!--右下-->
<Thumb Margin="0,0,-8,-8" Width="16" Height="16" HorizontalAlignment="Right" VerticalAlignment="Bottom" Cursor="SizeNWSE"/>
<!--左下-->
<Thumb Margin="-8,0,0,-8" Width="16" Height="16" HorizontalAlignment="Left" VerticalAlignment="Bottom" Cursor="SizeNESW"/>
</Grid>
</ac:AdornerHelper.AdornerContent>
</Border>
</Grid>
</Window>
效果预览
以上就是今天要讲的内容，在界面上定义装饰器主要目的是为了方编写复杂样式，使用方式有了较大的变化。想要灵活使用则需要对wpf有一定的深入了解。但从另外一个角度来说在界面上定义装饰器和使用Grid布局调整层叠达到相同效果，可能本质上区别不太大，至少在控件树上两者是一模一样的。总的来说个人觉得这是一种比较有意思的装饰器使用方法。
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