Using isolated storage for application-specific data in C# .NET Part 4: various

In the previous post we looked at how to find the location of a file when stored in isolated storage. We saw that isolated storage files have also a “normal” file path that you can navigate to in file explorer. The file paths are difficult to guess as they have complicated names but they are not secured in any way.

In this post we’ll briefly look at some various other things about isolated storage mainly related to size and quota.

Every application that uses isolated storage has a defined quota in bytes that it can use. Normally the default quota for partially trusted applications, e.g. those that you download from the internet, is 1MB. The IsolatedStorageFile object exposes a couple of properties that describe the quota, the available space and the size used:

IsolatedStorageFile applicationStorageFileForUser = IsolatedStorageFile.GetUserStoreForAssembly();
			
Debug.WriteLine(applicationStorageFileForUser.AvailableFreeSpace);
Debug.WriteLine(applicationStorageFileForUser.Quota);
Debug.WriteLine(applicationStorageFileForUser.UsedSize);

If the quota is not enough you can request a new upper limit using the IncreaseQuotaTo method of the IsolatedStorageFile class:

bool quotaIncreaseSuccess = applicationStorageFileForUser.IncreaseQuotaTo(some number);

The method will throw an exception if you’re trying to reduce the quota, i.e. set a lower number than the current quota.

Read all posts dedicated to file I/O here.

Using isolated storage for application-specific data in C# .NET Part 3: storage location

In this post we looked briefly at how to work with directories in isolated storage. In this post we’ll look at where isolated storage files are saved on disk depending on the isolation type: by user or by machine.

Recall our code to save the program settings specifically for the user:

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Using isolated storage for application-specific data in C# .NET Part 1: the basics

There’s a special storage location for a .NET application on Windows that is allocated to that application. It’s called isolated storage and it’s an optimal place to store files by an application that doesn’t have full access to the file system. Writing to and reading from isolated storage doesn’t require any extra security check. An application without full access to the file system will be able to use its allocated slot in isolated storage and nothing else. It’s an ideal mechanism for storing e.g. application state.

However, don’t confuse isolated storage with file security. It is still a “normal” location on disk with a file path. A typical location is under users/[username]/appdata/local. Therefore you or full-trust applications can still find and modify the files saved in isolated storage. However, limited-trust applications won’t be able to access any other part of the file system.

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