VirtualFile Class
Definition
Important
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Represents a file object in a virtual file or resource space.
public ref class VirtualFile abstract : System::Web::Hosting::VirtualFileBasepublic abstract class VirtualFile : System.Web.Hosting.VirtualFileBasetype VirtualFile = class
inherit VirtualFileBasePublic MustInherit Class VirtualFile
Inherits VirtualFileBase- Inheritance
Examples
The following code example is a VirtualFile class implementation that combines information stored in a DataSet object with a template file to return HTML data. This code example works with the code examples for the VirtualPathProvider and VirtualDirectory classes to provide virtual resources from a data store that is loaded into a DataSet object. For the complete instructions for compiling and running the example, see the Example section of the VirtualPathProvider class overview.
This example has three parts: the VirtualFile class implementation, an XML data file used to populate the DataSet object, and the page template file.
The first code example is an implementation of the VirtualFile class. Its constructor uses a method on a custom VirtualPathProvider object to return a DataSet object. It then searches the DataSet object to retrieve the information associated with the virtual file path provided. In the Open method, it combines the information from the DataSet object with a template file and returns the combination as a Stream object.
using System;
using System.Data;
using System.IO;
using System.Security.Permissions;
using System.Web;
using System.Web.Caching;
using System.Web.Hosting;
namespace Samples.AspNet.CS
{
[AspNetHostingPermission(SecurityAction.Demand, Level = AspNetHostingPermissionLevel.Minimal)]
[AspNetHostingPermission(SecurityAction.InheritanceDemand, Level = AspNetHostingPermissionLevel.Minimal)]
public class SampleVirtualFile : VirtualFile
{
private string content;
private SamplePathProvider spp;
public bool Exists
{
get { return (content != null); }
}
public SampleVirtualFile(string virtualPath, SamplePathProvider provider)
: base(virtualPath)
{
this.spp = provider;
GetData();
}
protected void GetData()
{
// Get the data from the SamplePathProvider
DataSet ds = spp.GetVirtualData();
// Get the virtual file from the resource table.
DataTable files = ds.Tables["resource"];
DataRow[] rows = files.Select(
String.Format("(name = '{0}') AND (type='file')", this.Name));
// If the select returned a row, store the file contents.
if (rows.Length > 0)
{
DataRow row = rows[0];
content = row["content"].ToString();
}
}
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;
}
}
}
Imports System.Data
Imports System.IO
Imports System.Security.Permissions
Imports System.Web
Imports System.Web.Caching
Imports System.Web.Hosting
Namespace Samples.AspNet.VB
<AspNetHostingPermission(SecurityAction.Demand, Level:=AspNetHostingPermissionLevel.Minimal), _
AspNetHostingPermission(SecurityAction.InheritanceDemand, level:=AspNetHostingPermissionLevel.Minimal)> _
Public Class SampleVirtualFile
Inherits VirtualFile
Private content As String
Private spp As SamplePathProvider
Public ReadOnly Property Exists() As Boolean
Get
Return (content <> String.Empty)
End Get
End Property
Public Sub New(ByVal virtualPath As String, ByVal provider As SamplePathProvider)
MyBase.New(virtualPath)
spp = provider
GetData()
End Sub
Protected Sub GetData()
' Get the data from the SamplePathProvider.
Dim spp As SamplePathProvider
spp = CType(HostingEnvironment.VirtualPathProvider, SamplePathProvider)
Dim ds As DataSet
ds = spp.GetVirtualData
' Get the virtual file data from the resource table.
Dim files As DataTable
files = ds.Tables("resource")
Dim rows As DataRow()
rows = files.Select( _
String.Format("(name='{0}') AND (type='file')", Me.Name))
' If the select returned a row, store the file contents.
If (rows.Length > 0) Then
Dim row As DataRow
row = rows(0)
content = row("content").ToString()
End If
End Sub
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
End Class
End Namespace
The second example is the XML data file used to populate the DataSet object returned by the custom VirtualPathProvider object. This XML data is used to demonstrate using the VirtualPathProvider, VirtualFile, and VirtualDirectory classes to retrieve data from external data, and is not intended to represent a production-quality data store.
<?xml version="1.0" encoding="utf-8" ?>
<resource type="dir"
path="/vrDir"
parentPath=""
content="">
<resource type="file"
path="/vrDir/Level1FileA.vrf"
parentPath="/vrDir"
content="This is the content of file Level1FileA.">
</resource>
<resource type="file"
path="/vrDir/Level1FileB.vrf"
parentPath="/vrDir"
content="This is the content of file Level1FileB.">
</resource>
<resource type="dir"
path="/vrDir/Level2DirA"
parentPath="/vrDir"
content="">
<resource type="file"
path="/vrDir/Level2DirA/Level2FileA.vrf"
parentPath="/vrDir/Level2DirA"
content="This is the content of file Level2FileA.">
</resource>
<resource type="file"
path="/vrDir/Level2DirA/Level2FileB.vrf"
parentPath="/vrDir/Level2DirA"
content="This is the content of file Level2FileB.">
</resource>
</resource>
<resource type="dir"
path="/vrDir/Level2DirB"
parentPath="/vrDir"
content="">
<resource type="file"
path="/vrDir/Level2DirB/Level2FileA.vrf"
parentPath="/vrDir/Level2DirB"
content="This is the content of file Level2FileA.">
</resource>
<resource type="file"
path="/vrDir/Level2DirB/Level2FileB.vrf"
parentPath="/vrDir/Level2DirB"
content="This is the content of file Level2FileB.">
</resource>
</resource>
</resource>
The third example is the text file used as a template for the virtual file. Placeholders in the file are represented by text between percent (%) marks, such as %file% and %content%. Timestamps are used to monitor changes to cached virtual file data.
<html>
<head>
<title>File name: %file%</title>
</head>
<body>
<h1>%file%</h1>
<p>%content%</p>
<p>Page timestamp: %pageTimestamp%<br>
Data timestamp: %dataTimestamp%<br>
Template timestamp: %templateTimestamp%</p>
</body>
</html>
Remarks
The VirtualFile class is the base class for objects that represent files in a virtual file system. Typically, you would implement a descendent of the VirtualFile class for each VirtualPathProvider object descendent in your Web application.
Notes to Implementers
When you inherit from the VirtualFile class, you must override the Open() method to return a read-only stream to the contents of the virtual resource.
Constructors
| VirtualFile(String) |
Initializes a new instance of the VirtualFile class. |
Properties
| IsDirectory |
Gets a value that indicates that this is a virtual resource that should be treated as a file. |
| Name |
Gets the display name of the virtual resource. (Inherited from VirtualFileBase) |
| VirtualPath |
Gets the virtual file path. (Inherited from VirtualFileBase) |
Methods
| CreateObjRef(Type) |
Creates an object that contains all the relevant information required to generate a proxy used to communicate with a remote object. (Inherited from MarshalByRefObject) |
| Equals(Object) |
Determines whether the specified object is equal to the current object. (Inherited from Object) |
| GetHashCode() |
Serves as the default hash function. (Inherited from Object) |
| GetLifetimeService() |
Obsolete.
Retrieves the current lifetime service object that controls the lifetime policy for this instance. (Inherited from MarshalByRefObject) |
| GetType() |
Gets the Type of the current instance. (Inherited from Object) |
| InitializeLifetimeService() |
Gives a VirtualFileBase instance an infinite lifetime by preventing a lease from being created. (Inherited from VirtualFileBase) |
| MemberwiseClone() |
Creates a shallow copy of the current Object. (Inherited from Object) |
| MemberwiseClone(Boolean) |
Creates a shallow copy of the current MarshalByRefObject object. (Inherited from MarshalByRefObject) |
| Open() |
When overridden in a derived class, returns a read-only stream to the virtual resource. |
| ToString() |
Returns a string that represents the current object. (Inherited from Object) |
