VirtualFile.Open 方法

定義

命名空間:

System.Web.Hosting

組件:

System.Web.dll

當在衍生類別中覆寫時，會將唯讀串流回傳給虛擬資源。

public:
 abstract System::IO::Stream ^ Open();

public abstract System.IO.Stream Open();

abstract member Open : unit -> System.IO.Stream

Public MustOverride Function Open () As Stream

傳回

Stream

一個只讀串流到虛擬檔案。

範例

以下程式碼範例是將虛擬檔案特定資訊與範本檔案結合，然後回傳組合的方法實作 Open 。 範本檔案會被快取，以減少多次讀取檔案系統以取得範本檔案的負擔。 關於執行範例所需的完整程式碼，請參閱類別總覽的 VirtualFile 範例部分。

private string FormatTimeStamp(DateTime time)
{
  return String.Format("{0} at {1}",
    time.ToLongDateString(), time.ToLongTimeString());
}

public override Stream Open()
{
  string templateFile = HostingEnvironment.ApplicationPhysicalPath + "App_Data\\template.txt";
  string pageTemplate;
  DateTime now = DateTime.Now;

  // Try to get the page template out of the cache.
  pageTemplate = (string)HostingEnvironment.Cache.Get("pageTemplate");

  if (pageTemplate == null)
  {
    // Get the page template.
    using (StreamReader reader = new StreamReader(templateFile))
    {
      pageTemplate = reader.ReadToEnd();
    }

    // Set template timestamp
    pageTemplate = pageTemplate.Replace("%templateTimestamp%", 
      FormatTimeStamp(now));

    // Make pageTemplate dependent on the template file.
    CacheDependency cd = new CacheDependency(templateFile);

    // Put pageTemplate into cache for maximum of 20 minutes.
    HostingEnvironment.Cache.Add("pageTemplate", pageTemplate, cd,
      Cache.NoAbsoluteExpiration,
      new TimeSpan(0, 20, 0),
      CacheItemPriority.Default, null);
  }

  // Put the page data into the template.
  pageTemplate = pageTemplate.Replace("%file%", this.Name);
  pageTemplate = pageTemplate.Replace("%content%", content);

  // Get the data time stamp from the cache.
  DateTime dataTimeStamp = (DateTime)HostingEnvironment.Cache.Get("dataTimeStamp");
  pageTemplate = pageTemplate.Replace("%dataTimestamp%", 
    FormatTimeStamp(dataTimeStamp));
  pageTemplate = pageTemplate.Replace("%pageTimestamp%", 
    FormatTimeStamp(now));

  // Put the page content on the stream.
  Stream stream = new MemoryStream();
  StreamWriter writer = new StreamWriter(stream);

  writer.Write(pageTemplate);
  writer.Flush();
  stream.Seek(0, SeekOrigin.Begin);

  return stream;
}

Private Function FormatTimeStamp(ByVal time As DateTime) As String
  Return String.Format("{0} at {1}", _
    time.ToLongDateString(), time.ToLongTimeString)
End Function

Public Overrides Function Open() As System.IO.Stream
  Dim templateFile As String
  templateFile = HostingEnvironment.ApplicationPhysicalPath & "App_Data\template.txt"

  Dim pageTemplate As String
  Dim now As DateTime
  now = DateTime.Now

  ' Try to get the page template out of the cache.
  pageTemplate = CType(HostingEnvironment.Cache.Get("pageTemplate"), String)

  If pageTemplate Is Nothing Then
    ' Get the page template.
    Try
      pageTemplate = My.Computer.FileSystem.ReadAllText(templateFile)
    Catch fileException As Exception
      Throw fileException
    End Try

    ' Set template timestamp.
    pageTemplate = pageTemplate.Replace("%templateTimestamp%", _
      FormatTimeStamp(Now))

    ' Make pageTemplate dependent on the template file.
    Dim cd As CacheDependency
    cd = New CacheDependency(templateFile)

    ' Put pageTemplate into cache for maximum of 20 minutes.
    HostingEnvironment.Cache.Add("pageTemplate", pageTemplate, cd, _
      Cache.NoAbsoluteExpiration, _
      New TimeSpan(0, 20, 0), _
      CacheItemPriority.Default, Nothing)
  End If

  ' Put the page data into the template.
  pageTemplate = pageTemplate.Replace("%file%", Me.Name)
  pageTemplate = pageTemplate.Replace("%content%", content)

  ' Get the data timestamp from the cache.
  Dim dataTimeStamp As DateTime
  dataTimeStamp = CType(HostingEnvironment.Cache.Get("dataTimeStamp"), DateTime)
  pageTemplate = pageTemplate.Replace("%dataTimestamp%", _
    FormatTimeStamp(dataTimeStamp))

  ' Set a timestamp for the page.
  Dim pageTimeStamp As String
  pageTimeStamp = FormatTimeStamp(now)
  pageTemplate = pageTemplate.Replace("%pageTimestamp%", pageTimeStamp)

  ' Put the page content on the stream.
  Dim stream As MemoryStream
  stream = New MemoryStream()

  Dim writer As StreamWriter
  writer = New StreamWriter(stream)

  writer.Write(pageTemplate)
  writer.Flush()
  stream.Seek(0, SeekOrigin.Begin)

  Return stream
End Function

備註

該方法回 Open 傳一個包含類別 VirtualPathProvider 視為檔案的資料的串流。 該串流是唯讀且可尋址的（該 CanSeek 性質為真）。

給實施者的注意事項

在導出類別中，方法 Open() 必須回傳可尋道的串流。 若方法回傳的串流不支援尋道，當串流傳遞給NotSupportedException物件以寫入資料時，會拋出 aHttpResponse。 例外發生是因為回應嘗試讀取該 Length 屬性，而在無法尋求的串流中，嘗試存取該屬性會導致異常。 如需詳細資訊，請參閱 CanSeek 屬性 (Property)。