RequirementAttribute 类
更新：2007 年 11 月
定义 RequirementValidator 类使用的属性。
命名空间： Microsoft.Windows.Design
程序集： Microsoft.Windows.Design.Extensibility（在 Microsoft.Windows.Design.Extensibility.dll 中）
语法
声明
Public MustInherit Class RequirementAttribute _
Inherits Attribute
用法
Dim instance As RequirementAttribute
public abstract class RequirementAttribute : Attribute
public ref class RequirementAttribute abstract : public Attribute
public abstract class RequirementAttribute extends Attribute
备注
可从 RequirementAttribute 抽象类派生以指定功能提供程序和功能连接器的要求。
RequirementValidator 检查类型中是否有 RequirementAttribute 属性。对于找到的每个 RequirementAttribute，它都调用 MeetsRequirement 抽象方法，传递 EditingContext 类的一个实例。RequiresServiceAttribute 等类派生自 RequirementAttribute 并检查上下文中是否存在指定的要求。
此系统允许设计器只激活可以在编辑上下文中成功运行的代码。
通过从 RequirementAttribute 派生并实现 MeetsRequirement 抽象方法来定义自定义要求。
示例
下面的代码示例演示如何通过使用派生自 RequirementAttribute 的 UsesItemPolicyAttribute 将自定义代理项策略附加到功能提供程序。有关完整的代码清单，请参见如何：创建代理项策略。
' The DockPanelAdornerProvider class implements an adorner
' that you can use to set the Margin property by using a
' drag operation. The DockPanelPolicy class enables a
' container policy for offering additional tasks and
' adorners on the panel's children.
<UsesItemPolicy(GetType(DockPanelPolicy))> _
Class DockPanelAdornerProvider
Inherits AdornerProvider
Public Sub New()
' The adorner is a Rectangle element.
Dim r As New Rectangle()
r.Width = 23.0
r.Height = 23.0
r.Fill = AdornerColors.GlyphFillBrush
' Set the rectangle's placement in the adorner panel.
Dim placement As New AdornerPlacementCollection()
placement.PositionRelativeToAdornerWidth(-1, 0)
placement.SizeRelativeToAdornerDesiredHeight(1.0, 0)
placement.SizeRelativeToAdornerDesiredWidth(1.0, 0)
placement.PositionRelativeToAdornerHeight(-1.0, 0)
AdornerPanel.SetPlacements(r, placement)
Dim p As New AdornerPanel()
p.Children.Add(r)
AdornerPanel.SetTask(r, New DockPanelMarginTask())
Adorners.Add(p)
End Sub
End Class
// The DockPanelAdornerProvider class implements an adorner
// that you can use to set the Margin property by using a
// drag operation. The DockPanelPolicy class enables a
// container policy for offering additional tasks and
// adorners on the panel's children.
[UsesItemPolicy(typeof(DockPanelPolicy))]
class DockPanelAdornerProvider : AdornerProvider
{
public DockPanelAdornerProvider()
{
// The adorner is a Rectangle element.
Rectangle r = new Rectangle();
r.Width = 23.0;
r.Height = 23.0;
r.Fill = AdornerColors.GlyphFillBrush;
// Set the rectangle's placement in the adorner panel.
AdornerPlacementCollection placement = new AdornerPlacementCollection();
placement.PositionRelativeToAdornerWidth(-1, 0);
placement.SizeRelativeToAdornerDesiredHeight(1.0, 0);
placement.SizeRelativeToAdornerDesiredWidth(1.0, 0);
placement.PositionRelativeToAdornerHeight(-1.0, 0);
AdornerPanel.SetPlacements(r, placement);
AdornerPanel p = new AdornerPanel();
p.Children.Add(r);
AdornerPanel.SetTask(r, new DockPanelMarginTask());
Adorners.Add(p);
}
}
继承层次结构
System.Object
System.Attribute
Microsoft.Windows.Design.RequirementAttribute
Microsoft.Windows.Design.Policies.UsesItemPolicyAttribute
Microsoft.Windows.Design.RequiresContextItemAttribute
Microsoft.Windows.Design.RequiresServiceAttribute
线程安全
此类型的任何公共 static（在 Visual Basic 中为 Shared） 成员都是线程安全的。但不保证所有实例成员都是线程安全的。