Light Up the Web with Silverlight by Jacek Ciereszko

Sunday, June 15, 2008 #

Isolated Storage Memory in Silverlight 2.0 RTW

In this article, I would like to describe Isolated Storage Memory in Silverlight 2.0 RTW. Isolated storage is a place on local disk, where applications have all access privileges to store their data. Default settings, give applications 1 MB space but this can be changed by administrator.

This memory space let application read files and create new, without special permissions. I used this feature, for example to store user settings (user name, application skins, etc.), local high scores for Silverlight game or as a flag in survey, to remember if user already voted today. It’s very useful and sooner or later you will use it ;)

Let’s dance

As an example, we will create simple demo, which will remember our name and will show it every time when we turn on application on our computer.

First, let's add two controls to "enter name":
<TextBox Height="32" x:Name="EnterName" Width="192" Text="Enter your name here" TextWrapping="Wrap"/>
<Button Height="28" x:Name="SubmitButton" Width="106" Foreground="#FF313131" Content="Submit" Click="SubmitButton_Click">

and one control to "show entered name"
<TextBlock Height="91" x:Name="NameTextBlock" Width="284" TextWrapping="Wrap" >
<Run x:Name="UserName" FontFamily="Comic Sans MS" FontSize="36" FontWeight="Bold" Text="" />
</TextBlock>

Then, add methods to write and read name from file in Isolated Storage. These methods are invoked from SubmitButton_Click event and from Page.Loaded event. To do this, we need IsolatedStorageFile object

IsolatedStorageFile isf = IsolatedStorageFile.GetUserStoreForApplication();

which we will use to check if file with user name exist

if (!isf.FileExists(“our_file.txt”))

and to create FileStream object

IsolatedStorageFileStream isfs = new IsolatedStorageFileStream(“our_file.txt”, FileMode.Open, isf);

Now, all we have to do is use for example StreamReader and make all operation like with simple text file on desktop application.

StreamReader sr = new StreamReader(isfs);
userName = sr.ReadToEnd();
sr.Close();

To save user's name in Isolated Storage, open file with different FileMode, for example

IsolatedStorageFileStream isfs = new IsolatedStorageFileStream(“our_file.txt”, FileMode.Create, isf);

and instead of StreamReader, use StreamWriter

StreamWriter sw = new StreamWriter(isfs);

All other parts of code for save method are similar to read parts.

Completed code for save method:
private void SaveUserName(string name)
{
     IsolatedStorageFile isf = IsolatedStorageFile.GetUserStoreForApplication();
     IsolatedStorageFileStream isfs = new IsolatedStorageFileStream(FILE_NAME, FileMode.Create, isf);
     StreamWriter sw = new StreamWriter(isfs);
     try
     {
            sw.WriteLine(String.Format("{0}", name));
     }
     catch (Exception ee) { }
     finally
     {
            sw.Close();
            isfs.Close();
            isfs.Dispose();
            isf.Dispose();
            sw.Dispose();
      }
}

Completed code for read method:
private string ReadNameIfExist()
{
      string userName = String.Empty;
      IsolatedStorageFile isf = IsolatedStorageFile.GetUserStoreForApplication();
      if (!isf.FileExists(FILE_NAME))
            return userName;

      IsolatedStorageFileStream isfs = new IsolatedStorageFileStream(FILE_NAME, FileMode.Open, isf);
      try
      {
            StreamReader sr = new StreamReader(isfs);
            userName = sr.ReadToEnd();
            sr.Close();
      }
      catch (Exception e) { }
      finally
      {
            isf.Dispose();
      }
      return userName;
}

Working example play demo - (remember to refresh web page F5)

Source code is below in “source code” section.

Where is that place

To find a place where exactly is our file with user's name, we have to use debugger in Visual Studio. Place breakpoint on isf variable and run application in debug mode.

Variable "m_AppFilePath" contain real path to Isolated Storage directory and file with user's name. This path is not easy to remember and it could looks like this

"C:\\Users\\ToJaUser\\AppData\\LocalLow\\Microsoft\\Silverlight\\is\\3tumcpvn.hf1\\wrelfaen.uut\\1\\s\\rtqyd4tgtuurqnzlqaf3otinrvcefdf4aeqlkxhw0dltde2t2uaaaeaa\\f"

Deleting isolated storage

If we don't want to keep any more data for Silverlight application in Isolated Storage, we can write program to clear this space or just click right button on any Silverlight application and choose "Silverlight Configuration"

Then go to "Application Storage" tab.

In this window we can see all information about every Silverlight application which saved data on our disk. We have also opportunity to delete these files with only one click.