WebPartTransformerAttribute 类

定义

public ref class WebPartTransformerAttribute sealed : Attribute

[System.AttributeUsage(System.AttributeTargets.Class)]
public sealed class WebPartTransformerAttribute : Attribute

[<System.AttributeUsage(System.AttributeTargets.Class)>]
type WebPartTransformerAttribute = class
    inherit Attribute

Public NotInheritable Class WebPartTransformerAttribute
Inherits Attribute

继承

Object

Attribute

WebPartTransformerAttribute

属性

AttributeUsageAttribute

示例

下面的代码示例演示如何对自定义WebPartTransformerAttribute类使用WebPartTransformer属性。 该特性指示该 RowToStringTransformer 类可以将类型的 IWebPartRow 提供程序连接点转换为类型的 IString使用者连接点。

此代码示例是类概述中找到的较大示例的 WebPartTransformer 一部分。

// A transformer that transforms a row to a string.
[AspNetHostingPermission(SecurityAction.Demand,
  Level = AspNetHostingPermissionLevel.Minimal)]
[AspNetHostingPermission(SecurityAction.InheritanceDemand,
  Level = AspNetHostingPermissionLevel.Minimal)]
[WebPartTransformer(typeof(IWebPartRow), typeof(IString))]
public class RowToStringTransformer : WebPartTransformer, IString
{

    private IWebPartRow _provider;
    private StringCallback _callback;

    private void GetRowData(object rowData)
    {
        PropertyDescriptorCollection props = _provider.Schema;
        if (props != null && props.Count > 0 && rowData != null)
        {
            string returnValue = String.Empty;
            foreach (PropertyDescriptor prop in props)
            {
                if (prop != props[0])
                {
                    returnValue += ", ";
                }
                returnValue += prop.DisplayName + ": " + prop.GetValue(rowData);
            }
            _callback(returnValue);
        }
        else
        {
            _callback(null);
        }
    }
    
    public override object Transform(object providerData)
    {
        _provider = (IWebPartRow)providerData;
        return this;
    }

    void IString.GetStringValue(StringCallback callback)
    {
        if (callback == null)
        {
            throw new ArgumentNullException("callback");
        }

        if (_provider != null)
        {
            _callback = callback;
            _provider.GetRowData(new RowCallback(GetRowData));
        }
        else
        {
            callback(null);
        }
    }
}

' A transformer that transforms a row to a string.
<AspNetHostingPermission(SecurityAction.Demand, _
   Level:=AspNetHostingPermissionLevel.Minimal)> _
<AspNetHostingPermission(SecurityAction.InheritanceDemand, _
   Level:=AspNetHostingPermissionLevel.Minimal)> _
<WebPartTransformer(GetType(IWebPartRow), GetType(IString))> _
Public Class RowToStringTransformer
    Inherits WebPartTransformer
    Implements IString

    Private _provider As IWebPartRow
    Private _callback As StringCallback

    Private Sub GetRowData(ByVal rowData As Object)
        Dim props As PropertyDescriptorCollection = _provider.Schema

        If ((Not (props Is Nothing)) AndAlso (props.Count > 0) _
          AndAlso (Not (rowData Is Nothing))) Then
            Dim returnValue As String = String.Empty
            For Each prop As PropertyDescriptor In props
                If Not (prop Is props(0)) Then
                    returnValue += ", "
                End If
                returnValue += prop.DisplayName.ToString() + ": " + _
                    prop.GetValue(rowData).ToString()
            Next
            _callback(returnValue)
        Else
            _callback(Nothing)
        End If
    End Sub

    Public Overrides Function Transform(ByVal providerData As Object) As Object
        _provider = CType(providerData, IWebPartRow)
        Return Me
    End Function


    Sub GetStringValue(ByVal callback As StringCallback) _
       Implements IString.GetStringValue
        If (callback Is Nothing) Then
            Throw New ArgumentNullException("callback")
        End If

        If (Not (_provider Is Nothing)) Then
            _callback = callback
            _provider.GetRowData(New RowCallback(AddressOf GetRowData))
        Else
            callback(Nothing)
        End If
    End Sub
End Class

注解

转换器用于转换两个 Web 部件控件与不兼容的连接点之间的数据。 连接点通过不同的接口提供或使用数据时不兼容。 例如，实现类型提供程序连接点的 IWebPartRow 提供程序无法直接连接到需要类型 IWebPartTable提供程序连接点的使用者。 相反，必须使用转换器来连接两个连接点。 可以通过从 WebPartTransformer 类派生类来创建自定义转换器。

该 WebPartTransformerAttribute 特性应用于类 WebPartTransformer 。 它定义提供程序连接点的类型和转换器支持的使用者连接点的类型。 转换器支持的使用者和提供程序连接点的类型必须与使用者和提供程序 Web 部件控件的连接点匹配，才能在控件之间建立连接。 在运行时，可以通过和GetConsumerType方法检索GetProviderType特定转换器支持的连接点的类型。