Appendix: Isolated Storage

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Isolated storage is a Microsoft® .NET feature that is used for lightweight data persistence. This appendix provides the explanation of isolated storage and then describes the limitations of isolated storage. Also covered is using isolated storage to persist user preferences and application state.

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Nội dung Text: Appendix: Isolated Storage

Appendix: Isolated Storage What Is Isolated Storage? Introduction Isolated storage is a Microsoft® .NET feature that is used for lightweight data persistence. This appendix provides the explanation of isolated storage and then describes the limitations of isolated storage. Also covered is using isolated storage to persist user preferences and application state. Isolated storage is an alternative to persistently storing data in a file or in a database. When a Web application stores data in a file, the file name and storage location must be chosen carefully. If the file name and storage location are not chosen carefully, there is a possibility that the storage location will be known to another Web application, which can then make the original Web application vulnerable to attack. Isolated storage manages this problem by providing a separate database storage mechanism that provides isolation by defining standardized ways of associating code with saved data. In isolated storage, data is stored in a logical storage compartment. Each storage compartment is isolated by some aspects of the code's identity. These identifying aspects of the code can include the application domain, assembly, and user. For the developer, the actual location of the storage compartment is transparent. Only the identity aspects are required to access the compartment. Uses in a Web Microsoft ASP.NET Web applications, by default, cannot use file input/output application (I/O). Isolated storage is useful in ASP.NET Web applications for storing user preferences and application state. Limitations Isolated storage is not a secure storage medium. Isolated storage is not protected from highly trusted code, from unmanaged code, or from trusted users. Isolated storage should not be used to store configuration settings that an administrator might want to control. Configuration files are a better location for configuration settings because they are more easily edited and installed by administrators. Isolated storage is a lightweight alternative to database storage when the number of users is small, when the overhead of a database is too high, or when a database is not available.
2 Appendix: Isolated Storage Using Isolated Storage Introduction Administrators can limit how much isolated storage should be available to a Web application or a user for use, based on the appropriate trust level. To create and access isolated storage, code must be granted the appropriate IsolatedStorageFilePermission attribute. Supporting types The System.IO.IsolatedStorage.IsolatedStorageFile class is used to create and access isolated storage compartments. This class contains methods that can be used for creating, opening, and deleting compartments, in addition to containing methods that can be used for adding folders to storage compartments. The System.IO.IsolatedStorage.IsolatedStorageFileStream class is used to open streams on files within isolated storage. These streams can then be used to read and write data to isolated storage. The following code segment uses the IsolatedStorageFile class to create a new store by using the User, Domain, and Assembly identities. The code segment then creates a new directory, named Files, within that store. The code then uses the IsolatedStorageFileStream class to create a new file in the Files directory. Finally, both the stream and the storage are closed, as shown in the following code example: [Visual Basic] Dim store As IsolatedStorageFile store = IsolatedStorageFile.GetStore( _ IsolatedStorageScope.User Or _ IsolatedStorageScope.Domain Or _ IsolatedStorageScope.Assembly, Nothing, Nothing) store.CreateDirectory("Files") Dim stream As IsolatedStorageFileStream stream = New IsolatedStorageFileStream("settings.txt", _ FileMode.Create, store) ' Use the Write method to set the file's contents. stream.Close() store.Close() [C#] IsolatedStorageFile store = IsolatedStorageFile.GetStore(IsolatedStorageScope.User | IsolatedStorageScope.Domain | IsolatedStorageScope.Assembly, null, null); store.CreateDirectory("Files"); IsolatedStorageFileStream stream = new IsolatedStorageFileStream("settings.txt", FileMode.Create, store); // // Use the Write method to set the file's contents stream.Close(); store.Close();
Appendix: Isolated Storage 3 StoreAdm.exe The isolated storage tool (StoreAdm.exe) is a command-line utility that can be used to list and delete isolated storage compartments on a computer. StoreAdm.exe supports the switches that are specified in the following table. Switch Description /list Lists the isolated storage for the current user. /remove Removes all of the existing isolated storage for the current user. /roaming Selects roaming storage. Assumes that roaming is supported by the underlying operating system. /quiet Changes the output to display only error messages and no informational messages. After running the preceding code in a console application named IsoStore.exe, the /list switch will provide the stores that are shown in the following code example: Microsoft (R) .NET Framework Store Admin 1.0.3705.0 Copyright (C) Microsoft Corporation 1998-2001. All rights reserved. Record #1 [Domain] file://C:/Demos/IsoStore.exe [Assembly] file://C:/Demos/IsoStore.exe Size : 2048
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