RequirementAttribute 類別

更新：2007 年 11 月

會定義 RequirementValidator 類別所使用的屬性。

命名空間： Microsoft.Windows.Design
組件： Microsoft.Windows.Design.Extensibility (在 Microsoft.Windows.Design.Extensibility.dll 中)

語法

Public MustInherit Class RequirementAttribute _
    Inherits Attribute

Dim instance As RequirementAttribute

public abstract class RequirementAttribute : Attribute

public ref class RequirementAttribute abstract : public Attribute

public abstract class RequirementAttribute extends Attribute

備註

您可以衍生自抽象 RequirementAttribute 類別，以指定功能提供者和功能連接器的需求。

RequirementValidator 會檢查型別中是否有 RequirementAttribute 屬性。針對它找到的每個 RequirementAttribute，它都會藉由傳遞 EditingContext 類別的執行個體來呼叫抽象 MeetsRequirement 方法。如 RequiresServiceAttribute 的類別會衍生自 RequirementAttribute 並檢查內容中是否有指定的需求。

這個系統允許設計工具只能啟動可以在編輯內容中順利執行的程式碼。

您可以衍生自 RequirementAttribute 並實作抽象 MeetsRequirement 方法，以定義自己的自訂需求。

範例

在下列程式碼範例中，會說明如何使用 UsesItemPolicyAttribute (衍生自 RequirementAttribute)，將自訂 Surrogate 原則附加至功能提供者。如需完整的程式碼清單，請參閱 HOW TO：建立 Surrogate 原則。

' 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);
    }
}