标签：知识点 09 value element static typeof new 全攻略 public
附加属性也是一种特殊的依赖属性。
Canvas中的Canvas.Left，Canvas.Top ，DockPanel中DockPanel.Dock等就是附加属性。
更加.NET类属性的写法经验。这个中可以直接点出来的，都是不用实例化的静态的。以Top属性为例：
public static readonly DependencyProperty TopProperty =
DependencyProperty.RegisterAttached("Top",
typeof(double), typeof(Canvas),
new FrameworkPropertyMetadata(0d,
FrameworkPropertyMetadataOptions.Inherits));
public static void SetTop(UIElement element, double value)
{
element.SetValue(TopProperty, value);
}
public static double GetTop(UIElement element)
{
return (double)element.GetValue(TopProperty);
}
看如下代码效果:
<Canvas Background="#AAAAAA" Height="150" Width="200">
<Rectangle Canvas.Left="50" Canvas.Top="50" Width="50" Height="50" Fill="Red" />
</Canvas>
代码中可以看到， Convas.Left附加属性实际作用在 Rectangle在Canvas中的Left属性上，Convas.Top附加属性实际作用在 Rectangle在Canvas中的Top属性上。
再来看一个例子：
<Grid>
<Grid.Clip>
<EllipseGeometry Center="400 200" RadiusX="160" RadiusY="200" />
</Grid.Clip>
<Image Source="ping.jpg" Stretch="Fill" />
</Grid>
通过Grid的附加属性Clip我们截取到了想要的图片效果。
那么什么时候去使用附加属性呢？下面是WPF经典Material Design主题开源项目Material Design In XAML Toolkit中对于阴影部分处理的源码。
public static class ShadowAssist
{
public static readonly DependencyProperty ShadowDepthProperty = DependencyProperty.RegisterAttached(
"ShadowDepth", typeof (ShadowDepth), typeof (ShadowAssist), new FrameworkPropertyMetadata(default(ShadowDepth), FrameworkPropertyMetadataOptions.AffectsRender));
public static void SetShadowDepth(DependencyObject element, ShadowDepth value)
{
element.SetValue(ShadowDepthProperty, value);
}
public static ShadowDepth GetShadowDepth(DependencyObject element)
{
return (ShadowDepth) element.GetValue(ShadowDepthProperty);
}
private static readonly DependencyPropertyKey LocalInfoPropertyKey = DependencyProperty.RegisterAttachedReadOnly(
"LocalInfo", typeof (ShadowLocalInfo), typeof (ShadowAssist), new PropertyMetadata(default(ShadowLocalInfo)));
private static void SetLocalInfo(DependencyObject element, ShadowLocalInfo value)
{
element.SetValue(LocalInfoPropertyKey, value);
}
private static ShadowLocalInfo GetLocalInfo(DependencyObject element)
{
return (ShadowLocalInfo) element.GetValue(LocalInfoPropertyKey.DependencyProperty);
}
public static readonly DependencyProperty DarkenProperty = DependencyProperty.RegisterAttached(
"Darken", typeof (bool), typeof (ShadowAssist), new FrameworkPropertyMetadata(default(bool), FrameworkPropertyMetadataOptions.AffectsRender, DarkenPropertyChangedCallback));
private static void DarkenPropertyChangedCallback(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs dependencyPropertyChangedEventArgs)
{
var uiElement = dependencyObject as UIElement;
var dropShadowEffect = uiElement?.Effect as DropShadowEffect;
if (dropShadowEffect == null) return;
if ((bool) dependencyPropertyChangedEventArgs.NewValue)
{
SetLocalInfo(dependencyObject, new ShadowLocalInfo(dropShadowEffect.Opacity));
var doubleAnimation = new DoubleAnimation(1, new Duration(TimeSpan.FromMilliseconds(350)))
{
FillBehavior = FillBehavior.HoldEnd
};
dropShadowEffect.BeginAnimation(DropShadowEffect.OpacityProperty, doubleAnimation);
}
else
{
var shadowLocalInfo = GetLocalInfo(dependencyObject);
if (shadowLocalInfo == null) return;
var doubleAnimation = new DoubleAnimation(shadowLocalInfo.StandardOpacity, new Duration(TimeSpan.FromMilliseconds(350)))
{
FillBehavior = FillBehavior.HoldEnd
};
dropShadowEffect.BeginAnimation(DropShadowEffect.OpacityProperty, doubleAnimation);
}
}
public static void SetDarken(DependencyObject element, bool value)
{
element.SetValue(DarkenProperty, value);
}
public static bool GetDarken(DependencyObject element)
{
return (bool) element.GetValue(DarkenProperty);
}
public static readonly DependencyProperty CacheModeProperty = DependencyProperty.RegisterAttached(
"CacheMode", typeof(CacheMode), typeof(ShadowAssist), new FrameworkPropertyMetadata(new BitmapCache { EnableClearType = true, SnapsToDevicePixels = true }, FrameworkPropertyMetadataOptions.Inherits));
public static void SetCacheMode(DependencyObject element, CacheMode value)
{
element.SetValue(CacheModeProperty, value);
}
public static CacheMode GetCacheMode(DependencyObject element)
{
return (CacheMode)element.GetValue(CacheModeProperty);
}
public static readonly DependencyProperty ShadowEdgesProperty = DependencyProperty.RegisterAttached(
"ShadowEdges", typeof(ShadowEdges), typeof(ShadowAssist), new PropertyMetadata(ShadowEdges.All));
public static void SetShadowEdges(DependencyObject element, ShadowEdges value)
{
element.SetValue(ShadowEdgesProperty, value);
}
public static ShadowEdges GetShadowEdges(DependencyObject element)
{
return (ShadowEdges) element.GetValue(ShadowEdgesProperty);
}
}
<Setter Property="wpf:ShadowAssist.ShadowDepth" Value="Depth1" />
谷歌提出的“材料设计” 理念中，阴影是比较重要的一部分，而该项目就是使用了附加属性来达到了效果。其中还有不少特性也是通过附加属性来完成的，给我如何使用附加属性，提供了比较好的模板。
可以参考学习：https://github.com/MaterialDesignInXAML/MaterialDesignInXamlToolkit
标签：知识点,09,value,element,static,typeof,new,全攻略,public 来源： https://www.cnblogs.com/kuangxiangnice/p/11071843.html
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