VirtualPathProvider Class
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Provides a set of methods that enable a Web application to retrieve resources from a virtual file system.
public ref class VirtualPathProvider abstract : MarshalByRefObject
public abstract class VirtualPathProvider : MarshalByRefObject
type VirtualPathProvider = class
inherit MarshalByRefObject
Public MustInherit Class VirtualPathProvider
Inherits MarshalByRefObject
- Inheritance
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.
Create a sample application on your Web server.
Copy the source code for the custom VirtualPathProvider object (see below) into a file in the application's
App_Code
directory.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.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.Copy the source code for the
AppStart
object (see below) into a file in the application'sApp_Code
directory.Copy the XML data (see below) into a file named
XMLData.xml
into a file in the application'sApp_Data
directory.Copy the
default.aspx
file (see below) into the root directory of the sample application. Use a Web browser to open thedefault.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);
}
}
}
}
Imports System.Data
Imports System.Security.Permissions
Imports System.Web
Imports System.Web.Caching
Imports System.Web.Hosting
Namespace Samples.AspNet.VB
<AspNetHostingPermission(SecurityAction.Demand, Level:=AspNetHostingPermissionLevel.Medium), _
AspNetHostingPermission(SecurityAction.InheritanceDemand, level:=AspNetHostingPermissionLevel.High)> _
Public Class SamplePathProvider
Inherits VirtualPathProvider
Private dataFile As String
Public Sub New()
MyBase.New()
End Sub
Protected Overrides Sub Initialize()
' Set the datafile path relative to the application's path.
dataFile = HostingEnvironment.ApplicationPhysicalPath & _
"App_Data\XMLData.xml"
End Sub
' Data set provider for the SampleVirtualFile and
' SampleVirtualDirectory classes. In a production application
' this method would be on a provider class that accesses
' the virtual resource data source.
' The System.Data.DataSet containing the virtual resources
' provided by the SamplePathProvider.
Public Function GetVirtualData() As DataSet
' Get the data from the cache.
Dim ds As DataSet
ds = CType(HostingEnvironment.Cache.Get("VPPData"), DataSet)
If ds Is Nothing Then
' Data set not in cache. Read XML file.
ds = New DataSet
ds.ReadXml(dataFile)
' Make DataSet dependent on XML file.
Dim cd As 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, Nothing)
' Set data timestamp.
Dim dataTimeStamp As DateTime
dataTimeStamp = DateTime.Now
' Cache it so we can get the timestamp in later calls.
HostingEnvironment.Cache.Add("dataTimeStamp", dataTimeStamp, Nothing, _
Cache.NoAbsoluteExpiration, _
New TimeSpan(0, 20, 0), _
CacheItemPriority.Default, Nothing)
End If
Return ds
End Function
Private Function IsPathVirtual(ByVal virtualPath As String) As Boolean
Dim checkPath As String
checkPath = VirtualPathUtility.ToAppRelative(virtualPath)
Return checkPath.StartsWith("~/vrdir", StringComparison.InvariantCultureIgnoreCase)
End Function
Public Overrides Function FileExists(ByVal virtualPath As String) As Boolean
If (IsPathVirtual(virtualPath)) Then
Dim file As SampleVirtualFile
file = CType(GetFile(virtualPath), SampleVirtualFile)
Return file.Exists
Else
Return Previous.FileExists(virtualPath)
End If
End Function
Public Overrides Function DirectoryExists(ByVal virtualDir As String) As Boolean
If (IsPathVirtual(virtualDir)) Then
Dim dir As SampleVirtualDirectory
dir = CType(GetDirectory(virtualDir), SampleVirtualDirectory)
Return dir.exists
Else
Return Previous.DirectoryExists(virtualDir)
End If
End Function
Public Overrides Function GetFile(ByVal virtualPath As String) As VirtualFile
If (IsPathVirtual(virtualPath)) Then
Return New SampleVirtualFile(virtualPath, Me)
Else
Return Previous.GetFile(virtualPath)
End If
End Function
Public Overrides Function GetDirectory(ByVal virtualDir As String) As VirtualDirectory
If (IsPathVirtual(virtualDir)) Then
Return New SampleVirtualDirectory(virtualDir, Me)
Else
Return Previous.GetDirectory(virtualDir)
End If
End Function
Public Overrides Function GetCacheDependency(ByVal virtualPath As String, ByVal virtualPathDependencies As IEnumerable, ByVal utcStart As Date) As CacheDependency
If (IsPathVirtual(virtualPath)) Then
Dim fullPathDependencies As System.Collections.Specialized.StringCollection
fullPathDependencies = Nothing
' Get the full path to all dependencies.
For Each virtualDependency As String In virtualPathDependencies
If fullPathDependencies Is Nothing Then
fullPathDependencies = New System.Collections.Specialized.StringCollection
End If
fullPathDependencies.Add(virtualDependency)
Next
If fullPathDependencies Is Nothing Then
Return Nothing
End If
Dim fullPathDependenciesArray As String()
fullPathDependencies.CopyTo(fullPathDependenciesArray, 0)
Return New CacheDependency(fullPathDependenciesArray, utcStart)
Else
Return Previous.GetCacheDependency(virtualPath, virtualPathDependencies, utcStart)
End If
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, 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);
}
}
}
Imports System.Web.Hosting
Namespace Samples.AspNet.VB
Public Class AppStart
Public Shared Sub AppInitialize()
Dim sampleProvider As SamplePathProvider = New SamplePathProvider()
HostingEnvironment.RegisterVirtualPathProvider(sampleProvider)
End Sub
End Class
End Namespace
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>
<%@ Page Language="VB" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<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>
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
, anyApp_LocalResources
.The application data folder,
App_Data
.
Nota
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.
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.
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.
-
Note: 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.
Virtual |
Initializes the class for use by an inherited class instance. This constructor can be called only by an inherited class. |
Previous |
Gets a reference to a previously registered VirtualPathProvider object in the compilation system. |
Combine |
Combines a base path with a relative path to return a complete path to a virtual resource. |
Create |
Creates an object that contains all the relevant information required to generate a proxy used to communicate with a remote object. (Inherited from MarshalByRefObject) |
Directory |
Gets a value that indicates whether a directory exists in the virtual file system. |
Equals(Object) |
Determines whether the specified object is equal to the current object. (Inherited from Object) |
File |
Gets a value that indicates whether a file exists in the virtual file system. |
Get |
Creates a cache dependency based on the specified virtual paths. |
Get |
Returns a cache key to use for the specified virtual path. |
Get |
Gets a virtual directory from the virtual file system. |
Get |
Gets a virtual file from the virtual file system. |
Get |
Returns a hash of the specified virtual paths. |
Get |
Serves as the default hash function. (Inherited from Object) |
Get |
Obsolete.
Retrieves the current lifetime service object that controls the lifetime policy for this instance. (Inherited from MarshalByRefObject) |
Get |
Gets the Type of the current instance. (Inherited from Object) |
Initialize() |
Initializes the VirtualPathProvider instance. |
Initialize |
Gives the VirtualPathProvider object an infinite lifetime by preventing a lease from being created. |
Memberwise |
Creates a shallow copy of the current Object. (Inherited from Object) |
Memberwise |
Creates a shallow copy of the current MarshalByRefObject object. (Inherited from MarshalByRefObject) |
Open |
Returns a stream from a virtual file. |
To |
Returns a string that represents the current object. (Inherited from Object) |
Produto | Versões |
---|---|
.NET Framework | 2.0, 3.0, 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1 |
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