AggregateCacheDependency 類別

定義

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

繼承

Object

CacheDependency

AggregateCacheDependency

範例

以下程式碼範例利用該 AggregateCacheDependency 類別，將 DataSet一個名為 XMLDataSet、 的快取加入，該快取依賴於文字檔與 XML 檔案。

   ' 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

備註

該 AggregateCacheDependency 類別監控一組相依物件，當其中任何物件變更時，快取的項目會自動移除。 陣列中的物件可以是 CacheDependency 物件、 SqlCacheDependency 物件、衍生自 CacheDependency的自訂物件，或這些組合的任意組合。

這個 AggregateCacheDependency 類別與類別 CacheDependency 的不同之處在於，它允許你將多個不同類型的相依關係關聯到單一快取項目。 例如，如果你建立一個頁面，從SQL Server資料庫資料表和 XML 檔案匯入資料，你可以建立一個 SqlCacheDependency 物件來表示對資料庫資料表的依賴，並建立一個 CacheDependency 來表示對 XML 檔案的依賴。 你不必為每個依賴性呼叫 Cache.Insert 方法，而是建立一個包含每個依賴的類別實例 AggregateCacheDependency 。 接著你可以用單一 Insert 呼叫讓頁面依賴於實 AggregateCacheDependency 例。