VirtualPathProvider Class
Assembly: System.Web (in system.web.dll)
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:
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ASP.NET pages, master pages, user controls, and other objects.
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Standard Web pages with extensions such as .htm and .jpg.
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Any custom extension mapped to a BuildProvider instance.
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Any named theme in the
App_Themefolder.
You cannot store ASP.NET application folders or files that generate application-level assemblies in a virtual file system. This includes:
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The Global.asax file.
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Web.config files.
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Site map data files used by the XmlSiteMapProvider.
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Directories that contain application assemblies or that generate application assemblies:
Bin,App_Code,App_GlobalResources, anyApp_LocalResources. -
The application data folder,
App_Data.
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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.
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If your virtual file system will contain themes for the Web site (by creating a virtual |
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.
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Create a sample application on your Web server.
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Copy the source code for the custom VirtualPathProvider object (see below) into a file in the application's
App_Codedirectory. -
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_Codedirectory. -
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_Codedirectory. -
Copy the source code for the
AppStartobject (see below) into a file in the application'sApp_Codedirectory. -
Copy the XML data (see below) into a file named
XMLData.xmlinto a file in the application'sApp_Datadirectory. -
Copy the
default.aspxfile (see below) into the root directory of the sample application. Use a Web browser to open thedefault.aspxfile, 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.
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.
The last example is an ASP.NET page that contains links to the virtual files contained in the virtual file system.
- AspNetHostingPermission for operating in a hosted environment. Demand value: LinkDemand. Permission value: Medium.
- AspNetHostingPermission for operating in a hosted environment. Demand value: InheritanceDemand. Permission value: High.
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