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VirtualPathProvider Class

Provides a set of methods that enable a Web application to retrieve resources from a virtual file system.

System.Object
  System.MarshalByRefObject
    System.Web.Hosting.VirtualPathProvider

Namespace:  System.Web.Hosting
Assembly:  System.Web (in System.Web.dll)

public abstract class VirtualPathProvider : MarshalByRefObject

The VirtualPathProvider type exposes the following members.

  NameDescription
Protected methodVirtualPathProviderInitializes the class for use by an inherited class instance. This constructor can be called only by an inherited class.
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  NameDescription
Protected propertyPreviousGets a reference to a previously registered VirtualPathProvider object in the compilation system.
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  NameDescription
Public methodCombineVirtualPathsCombines a base path with a relative path to return a complete path to a virtual resource.
Public methodCreateObjRefCreates an object that contains all the relevant information required to generate a proxy used to communicate with a remote object. (Inherited from MarshalByRefObject.)
Public methodDirectoryExistsGets a value that indicates whether a directory exists in the virtual file system.
Public methodEquals(Object)Determines whether the specified object is equal to the current object. (Inherited from Object.)
Public methodFileExistsGets a value that indicates whether a file exists in the virtual file system.
Protected methodFinalizeAllows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Public methodGetCacheDependencyCreates a cache dependency based on the specified virtual paths.
Public methodGetCacheKeyReturns a cache key to use for the specified virtual path.
Public methodGetDirectoryGets a virtual directory from the virtual file system.
Public methodGetFileGets a virtual file from the virtual file system.
Public methodGetFileHashReturns a hash of the specified virtual paths.
Public methodGetHashCodeServes as the default hash function. (Inherited from Object.)
Public methodGetLifetimeServiceRetrieves the current lifetime service object that controls the lifetime policy for this instance. (Inherited from MarshalByRefObject.)
Public methodGetTypeGets the Type of the current instance. (Inherited from Object.)
Protected methodInitializeInitializes the VirtualPathProvider instance.
Public methodInitializeLifetimeServiceGives the VirtualPathProvider object an infinite lifetime by preventing a lease from being created. (Overrides MarshalByRefObject.InitializeLifetimeService().)
Protected methodMemberwiseClone()Creates a shallow copy of the current Object. (Inherited from Object.)
Protected methodMemberwiseClone(Boolean)Creates a shallow copy of the current MarshalByRefObject object. (Inherited from MarshalByRefObject.)
Public methodStatic memberOpenFileReturns a stream from a virtual file.
Public methodToStringReturns a string that represents the current object. (Inherited from Object.)
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The VirtualPathProvider class provides a set of methods for implementing a virtual file system for a Web application. In a virtual file system, the files and directories are managed by a data store other than the file system provided by the server's operating system. For example, you can use a virtual file system to store content in a SQL Server database.

You can store any file that is processed on request in a virtual file system. This includes:

  • ASP.NET pages, master pages, user controls, and other objects.

  • Standard Web pages with extensions such as .htm and .jpg.

  • Any custom extension mapped to a BuildProvider instance.

  • Any named theme in the App_Theme folder.

You cannot store ASP.NET application folders or files that generate application-level assemblies in a virtual file system. This includes:

  • The Global.asax file.

  • Web.config files.

  • Site map data files used by the XmlSiteMapProvider.

  • Directories that contain application assemblies or that generate application assemblies: Bin, App_Code, App_GlobalResources, any App_LocalResources.

  • The application data folder, App_Data.

NoteNote

If a Web site is precompiled for deployment, content provided by a VirtualPathProvider instance is not compiled, and no VirtualPathProvider instances are used by the precompiled site.

Registering a VirtualPathProvider

A custom VirtualPathProvider instance should be registered with the ASP.NET compilation system by using the HostingEnvironment.RegisterVirtualPathProvider method before any page parsing or compilation is performed by the Web application.

Typically, a VirtualPathProvider instance is registered in an AppInitialize method defined in the App_Code directory, or during the Application_Start event in the Global.asax file. For an example of registering a VirtualPathProvider instance in an AppInitialize method, see the Example section.

You can register a VirtualPathProvider instance during other events, but pages compiled and cached before the VirtualPathProvider instance is registered will not be invalidated, even if the new VirtualPathProvider instance would now provide the source for the previously compiled page.

Notes to Inheritors

When you inherit from VirtualPathProvider, you must override the following members:

If your custom VirtualPathProvider class supports directories in the virtual file system, you must override the following members.

NoteNote

If your virtual file system will contain themes for the Web site (by creating a virtual App_Themes directory), your custom VirtualPathProvider class must support directories.

A custom VirtualPathProvider class works with classes derived from the VirtualFile and VirtualDirectory classes. You should implement derived classes from these types to provide file and directory information from your virtual file system. For an example of a custom VirtualFile implementation, see the Example section of the VirtualFile class overview topic. For an example of a custom VirtualDirectory implementation, see the Example section of the VirtualDirectory class overview topic.

The following code example is a VirtualPathProvider class implementation that creates a virtual file system using information stored in a DataSet object. The code example works with the code examples for the VirtualFile and VirtualDirectory classes to provide virtual resources from a data store that is loaded into a DataSet object.

This example has four parts: the VirtualPathProvider class implementation, an XML data file used to populate the DataSet object, an AppStart object that contains an AppInitialize method used to register the VirtualPathProvider class with the compilation system, and an ASP.NET page that provides links to the virtual files.

To use this sample code in an application, follow these steps.

  1. Create a sample application on your Web server.

  2. Copy the source code for the custom VirtualPathProvider object (see below) into a file in the application's App_Code directory.

  3. Copy the source code for the custom VirtualDirectory object (see the Example section in the VirtualDirectory class overview topic) into a file in the application's App_Code directory.

  4. Copy the source code for the custom VirtualFile object (see the Example section in the VirtualFile class overview topic) into a file in the application's App_Code directory.

  5. Copy the source code for the AppStart object (see below) into a file in the application's App_Code directory.

  6. Copy the XML data (see below) into a file named XMLData.xml into a file in the application's App_Data directory.

  7. Copy the default.aspx file (see below) into the root directory of the sample application. Use a Web browser to open the default.aspx file, and then click the links on the page to see the contents of the virtual files.

The first example is a custom VirtualPathProvider class. The DirectoryExists and FileExists methods are overridden to indicate whether a requested directory is present in the virtual file system. The GetDirectory and GetFile methods are overridden to return custom VirtualDirectory and VirtualFile instances containing information from the virtual file system.

The class also provides a GetVirtualData method used by the VirtualDirectory and VirtualFile classes to access the DataSet object containing the virtual file system data. In a production implementation, this method would typically be implemented in a business object responsible for interacting with the data store.

using System;
using System.Data;
using System.Security.Permissions;
using System.Web;
using System.Web.Caching;
using System.Web.Hosting;

namespace Samples.AspNet.CS
{
  [AspNetHostingPermission(SecurityAction.Demand, Level = AspNetHostingPermissionLevel.Medium)]
  [AspNetHostingPermission(SecurityAction.InheritanceDemand, Level = AspNetHostingPermissionLevel.High)]
  public class SamplePathProvider : VirtualPathProvider
  {
    private string dataFile;

    public SamplePathProvider()
      : base()
    {
    }

    protected override void Initialize()
    {
      // Set the datafile path relative to the application's path.
      dataFile = HostingEnvironment.ApplicationPhysicalPath + "App_Data\\XMLData.xml";
    }

    /// <summary> 
    ///   Data set provider for the SampleVirtualDirectory and 
    ///   SampleVirtualFile classes. In a production application 
    ///   this method would be on a provider class that accesses 
    ///   the virtual resource data source. 
    /// </summary> 
    /// <returns> 
    ///   The System.Data.DataSet containing the virtual resources  
    ///   provided by the SamplePathProvider. 
    /// </returns> 
    public DataSet GetVirtualData()
    {
      // Get the data from the cache.
      DataSet ds = (DataSet)HostingEnvironment.Cache.Get("VPPData");
      if (ds == null)
      {
        // Data not in cache. Read XML file.
        ds = new DataSet();
        ds.ReadXml(dataFile);

        // Make DataSet dependent on XML file.
        CacheDependency cd = new CacheDependency(dataFile);

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

        // Set data timestamp.
        DateTime dataTimeStamp = DateTime.Now;
        // Cache it so we can get the timestamp in later calls.
        HostingEnvironment.Cache.Insert("dataTimeStamp", dataTimeStamp, null,
          Cache.NoAbsoluteExpiration,
          new TimeSpan(0, 20, 0),
          CacheItemPriority.Default, null);
      }
      return ds;
    }

    /// <summary> 
    ///   Determines whether a specified virtual path is within 
    ///   the virtual file system. 
    /// </summary> 
    /// <param name="virtualPath">An absolute virtual path.</param>
    /// <returns> 
    ///   true if the virtual path is within the  
    ///   virtual file sytem; otherwise, false. 
    /// </returns> 
    private bool IsPathVirtual(string virtualPath)
    {
      String checkPath = VirtualPathUtility.ToAppRelative(virtualPath);
      return checkPath.StartsWith("~/vrdir", StringComparison.InvariantCultureIgnoreCase);
    }

    public override bool FileExists(string virtualPath)
    {
      if (IsPathVirtual(virtualPath))
      {
        SampleVirtualFile file = (SampleVirtualFile)GetFile(virtualPath);
        return file.Exists;
      }
      else 
        return Previous.FileExists(virtualPath);
    }

    public override bool DirectoryExists(string virtualDir)
    {
      if (IsPathVirtual(virtualDir))
      {
        SampleVirtualDirectory dir = (SampleVirtualDirectory)GetDirectory(virtualDir);
        return dir.Exists;
      }
      else 
        return Previous.DirectoryExists(virtualDir);
    }

    public override VirtualFile GetFile(string virtualPath)
    {
      if (IsPathVirtual(virtualPath))
        return new SampleVirtualFile(virtualPath, this);
      else 
        return Previous.GetFile(virtualPath);
    }

    public override VirtualDirectory GetDirectory(string virtualDir)
    {
      if (IsPathVirtual(virtualDir))
        return new SampleVirtualDirectory(virtualDir, this);
      else 
        return Previous.GetDirectory(virtualDir);
    }

    public override CacheDependency GetCacheDependency(
      string virtualPath, 
      System.Collections.IEnumerable virtualPathDependencies, 
      DateTime utcStart)
    {
      if (IsPathVirtual(virtualPath))
      {
        System.Collections.Specialized.StringCollection fullPathDependencies = null;

        // Get the full path to all dependencies. 
        foreach (string virtualDependency in virtualPathDependencies)
        {
          if (fullPathDependencies == null)
            fullPathDependencies = new System.Collections.Specialized.StringCollection();

          fullPathDependencies.Add(virtualDependency);
        }
        if (fullPathDependencies == null)
          return null;

        // Copy the list of full-path dependencies into an array. 
        string[] fullPathDependenciesArray = new string[fullPathDependencies.Count];
        fullPathDependencies.CopyTo(fullPathDependenciesArray, 0);
        // Copy the virtual path into an array. 
        string[] virtualPathArray = new string[1];
        virtualPathArray[0] = virtualPath;

        return new CacheDependency(virtualPathArray, fullPathDependenciesArray, utcStart);
      }
      else 
        return Previous.GetCacheDependency(virtualPath, virtualPathDependencies, utcStart);
    }
  }
  

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, VirtualDirectory, and VirtualFile objects 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 provides an AppStart object that contains an AppInitialize method. This method is called during the initialization of an ASP.NET application to perform any custom initialization required. In this case, it registers the custom VirtualPathProvider object with the ASP.NET build system.

using System.Web.Hosting;

namespace Samples.AspNet.CS
{
  /// <summary> 
  ///   Contains the application initialization method 
  ///   for the sample application. 
  /// </summary> 
  public static class AppStart
  {
    public static void AppInitialize()
    {
      SamplePathProvider sampleProvider = new SamplePathProvider();
      HostingEnvironment.RegisterVirtualPathProvider(sampleProvider);
    } 
  }
}

The last example is an ASP.NET page that contains links to the virtual files contained in the virtual file system.


<%@ Page Language="C#" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<script runat="server">

</script>

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
  <meta http-equiv="Content-Type" content="text/html" />
  <title>Virtual Path Provider Example</title>
</head>
<body>
  <form id="form1" runat="server">
    <asp:HyperLink ID="hyperLink1" runat="server" NavigateUrl="vrDir/Level1FileA.vrf" Text="Level 1, File A" /><br />
    <asp:HyperLink ID="hyperLink2" runat="server" NavigateUrl="vrDir/Level1FileB.vrf" Text="Level 1, File B" /><br />
    <asp:HyperLink ID="hyperLink3" runat="server" NavigateUrl="vrDir/Level2DirA/Level2FileA.vrf" Text="Level 2a, File A" /><br />
    <asp:HyperLink ID="hyperLink4" runat="server" NavigateUrl="vrDir/Level2DirA/Level2FileB.vrf" Text="Level 2a, File B" /><br />
    <asp:HyperLink ID="hyperLink5" runat="server" NavigateUrl="vrDir/Level2DirB/Level2FileA.vrf" Text="Level 2b, File A" /><br />
    <asp:HyperLink ID="hyperLink6" runat="server" NavigateUrl="vrDir/Level2DirB/Level2FileB.vrf" Text="Level 2b, File B" /><br />
  </form>
</body>
</html>

.NET Framework

Supported in: 4.5.2, 4.5.1, 4.5, 4, 3.5, 3.0, 2.0

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.
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