AggregateCacheDependency 类

定义

public ref class AggregateCacheDependency sealed : System::Web::Caching::CacheDependency

public sealed class AggregateCacheDependency : System.Web.Caching.CacheDependency

type AggregateCacheDependency = class
    inherit CacheDependency

Public NotInheritable Class AggregateCacheDependency
Inherits CacheDependency

继承

Object

CacheDependency

AggregateCacheDependency

示例

下面的代码示例使用AggregateCacheDependency类向依赖于文本文件和 XML 文件的缓存添加命名DataSetXMLDataSet名称。

   ' When the page is loaded, use the 
   ' AggregateCacheDependency class to make 
   ' a cached item dependent on two files.
   
   Sub Page_Load(sender As Object, e As EventArgs)
      Dim Source As DataView
   
      Source = Cache("XMLDataSet")
   
      If Source Is Nothing
             Dim DS As New DataSet
             Dim FS As FileStream
             Dim Reader As StreamReader
             Dim txtDep As CacheDependency
             Dim xmlDep As CacheDependency
             Dim aggDep As AggregateCacheDependency
   
   
             FS = New FileStream(Server.MapPath("authors.xml"),FileMode.Open,FileAccess.Read)
             Reader = New StreamReader(FS)
             DS.ReadXml(Reader)
             FS.Close()
   
             Source = new DataView(ds.Tables(0))
            ' Create two CacheDependency objects, one to a
            ' text file and the other to an XML file. 
            ' Create a CacheDependency array with these 
            ' two objects as items in the array.
             txtDep = New CacheDependency(Server.MapPath("Storage.txt"))
             xmlDep = New CacheDependency(Server.MapPath("authors.xml"))
             Dim DepArray() As CacheDependency = {txtDep, xmlDep}

             ' Create an AggregateCacheDependency object and 
             ' use the Add method to add the array to it.   
             aggDep = New AggregateCacheDependency()
             aggDep.Add(DepArray)
   
             ' Call the GetUniqueId method to generate
             ' an ID for each dependency in the array.
             msg1.Text = aggDep.GetUniqueId()
             
             ' Add the new data set to the cache with 
             ' dependencies on both files in the array.
             Cache.Insert("XMLDataSet", Source, aggDep)
             If aggDep.HasChanged = True Then
                chngMsg.Text = "The dependency changed at: " & DateTime.Now
   
             Else
                chngMsg.Text = "The dependency changed last at: " & aggDep.UtcLastModified.ToString()
             End If

   
             cacheMsg1.Text = "Dataset created explicitly"
           Else
             cacheMsg1.Text = "Dataset retrieved from cache"
           End If
   
   
             MyLiteral.Text = Source.Table.TableName
             MyDataGrid.DataSource = Source
             MyDataGrid.DataBind()
         End Sub
 

         Public Sub btn_Click(sender As Object, e As EventArgs )
   
          If (MyTextBox.Text = String.Empty) Then
             msg2.Text ="You have not changed the text file."
          Else
             msg2.Text="You added " & MyTextBox.Text & "."
   
             ' Create an instance of the StreamWriter class
             ' to write text to a file.
             Dim sw As StreamWriter
             sw = File.CreateText(Server.MapPath("Storage.txt"))
   
             ' Add some text to the file.
             sw.Write("You entered:")
             sw.WriteLine(MyTextBox.Text)
   
             ' Write arbitrary objects to the file as needed.
             sw.Write("Text added at:")
             sw.WriteLine(DateTime.Now)
             sw.WriteLine("-------------------")
             sw.Close()
          End If
        End Sub

注解

该 AggregateCacheDependency 类监视依赖项对象的集合，以便在其中任何一个对象发生更改时自动删除缓存的项。 数组中的对象可以是 CacheDependency 对象、 SqlCacheDependency 对象、派生自 CacheDependency的自定义对象或这些对象的任何组合。

该 AggregateCacheDependency 类与 CacheDependency 类不同，因为它允许将不同类型的多个依赖项与单个缓存项相关联。 例如，如果创建一个从SQL Server数据库表和 XML 文件导入数据的页，则可以创建一个 SqlCacheDependency 对象来表示数据库表的依赖项，CacheDependency 表示对 XML 文件的依赖。 可以为每个依赖项创建一个 Cache.Insert 类的 AggregateCacheDependency 实例，而不是对每个依赖项进行方法调用。 然后，可以使用单个 Insert 调用使页面依赖于 AggregateCacheDependency 实例。