State Management is Silverlight using Isolated Storage


State management is the process to maintain state and page information over multiple requests for the same or different pages. Web applications are based on stateless HTTP protocol so web form pages do not automatically indicate whether the requests in a sequence are all from the same client or even whether a single browser instance is still actively viewing a page or site. A new instance of the Web page class is created each time the page is requested and with each round trip to the server pages are destroyed and re-created.

ASP.NET includes several options that help to preserve data on both a per-page basis and an application-wide basis.

Client-Side Method State Management

1. View state 2.Control state 3.Hidden fields 4.Cookies 5. Query string

Server-Side Method State Management

1. Application state 2.Session state 3.Profile properties 4. Database support

State management in Silverlight 2 can be done using the concept of Isolated storage. In Silverlight application everything is compiled in one XAP file and when a user requests this is copied to the client machine. So there are no server round trips and page request every time, this reduces the need of maintaining the use or application state. But in typical business application state management may be required.

Silverlight Isolated Storage

Isolated storage is a data storage mechanism that helps in storing data on the client machine in a hidden folder outside the browser’s cache. Silverlight Applications runs as partial trust but isolated storage API is allowed to create and access files that are stored in an Isolated Storage area which act as non volatile cache and is shared across the browsers. Every application has its own portion of the isolated storage with a default size of 1MB and can be used to store user specific information as name, preferences and skins etc. It can be used as Client-Side state management.

Demo

Location of Isolated Storage in Vista
%:\Users\%\AppData\LocalLow\Microsoft\Silverlight\is

Location of Isolated Storage in Windows XP
%:\Documents and Settings\%\Local Settings\Application Data\Microsoft\Silverlight\is

Retrieve Isolated Storage Information (Quota, Available Space)
private void ButtonShowInfo_Click(object sender, RoutedEventArgs e)

        {

            try

            {

                using (var store = IsolatedStorageFile.GetUserStoreForApplication())

                {

                    string spaceUsed = (store.Quota - store.AvailableFreeSpace).ToString();

                    string spaceAvailable = store.AvailableFreeSpace.ToString();

                    string currentQuota = store.Quota.ToString();

                    string message = String.Format("Quota: {0} bytes, Used: {1} bytes, Available: {2} bytes", currentQuota, spaceUsed, spaceAvailable);

                    TextBoxResults.Text = message;

                    SaveLogToIsolatedStorage(message);

                }

            }

            catch (IsolatedStorageException)

            {

                TextBoxResults.Text = "Unable to access Isolated Storage.";

                SaveLogToIsolatedStorage("Unable to access Isolated Storage.");

            }

        }

Create a variable for IsolatedStorageSettings
//Create a variable for IsolatedStorageSettings

//IsolatedStorageSettings contains the contents of the application IsolatedStorageFile scoped at the application level

        private IsolatedStorageSettings isoStorSettings = IsolatedStorageSettings.ApplicationSettings;

Save information in Isolated Storage
private void ButtonSave_Click(object sender, RoutedEventArgs e)

        {

            try

            {

                User user = new User();

                user.Name = TextBoxName.Text;

                user.Designation = TextBoxDesignation.Text;

                user.Address = TextBoxAddress.Text;

                user.City = TextBoxCity.Text;

                isoStorSettings.Add("UserDetail", user);

                TextBoxResults.Text = "User Detaild stored.";

                SaveLogToIsolatedStorage("User Detaild stored.");

            }

            catch (ArgumentException ex)

            {

                TextBoxResults.Text = ex.Message;

                SaveLogToIsolatedStorage(ex.Message);

            }

        }

Retrieve information from Isolated Storage
private void ButtonRetrieve_Click(object sender, RoutedEventArgs e)

        {

            try

            {

                User user = (User)isoStorSettings["UserDetail"];

                TextBoxName.Text = user.Name;

                TextBoxDesignation.Text = user.Designation;

                TextBoxAddress.Text = user.Address;

                TextBoxCity.Text = user.City;

                TextBoxResults.Text = "User Details retrieved.";

                SaveLogToIsolatedStorage("User Details retrieved.");

            }

            catch (System.Collections.Generic.KeyNotFoundException ex)

            {

                TextBoxResults.Text = ex.Message;

                SaveLogToIsolatedStorage(ex.Message);

                ClearTextBoxes();

            }

        }

Delete from Isolated Storage
private void ButtonDelete_Click(object sender, RoutedEventArgs e)

        {

            isoStorSettings.Remove("UserDetail");

            TextBoxResults.Text = "User Detaild deleted.";

            SaveLogToIsolatedStorage("User Detaild deleted.");

            ClearTextBoxes();

        }

Increase the Isolated Storage space
private void ButtonIncreaseAllocation_Click(object sender, RoutedEventArgs e)

        {

            try

            {

                using (var store = IsolatedStorageFile.GetUserStoreForApplication())

                {

                    // Request more space in bytes.

                    Int64 spaceToAdd = 1 * 1024 * 1024;

                    Int64 currentAvailable = store.AvailableFreeSpace;

 

                    // If available space is less than requested, then increase.

                    if (currentAvailable < spaceToAdd)

                    {

                        // Request more quota space.

                        if (!store.IncreaseQuotaTo(store.Quota + spaceToAdd))

                        {

                            // The user clicked NO to the host's prompt to approve the quota increase.

                            TextBoxResults.Text = "User declined to approve Quota inrease";

                            SaveLogToIsolatedStorage("User declined to approve Quota inrease");

                        }

                        else

                        {

                            // The user clicked YES to the host's prompt to approve the quota increase.

                            TextBoxResults.Text = "Quota inreased";

                            SaveLogToIsolatedStorage("Quota inreased");

                        }

                    }

                    else

                    {

                        string messge = String.Format("{0:0.00} MB is still available.", (decimal)currentAvailable / 1024 / 1024);

                        TextBoxResults.Text = messge;

                        SaveLogToIsolatedStorage(messge);

                    }

                }

            }

            catch (IsolatedStorageException ex)

            {

                TextBoxResults.Text = ex.Message;

                SaveLogToIsolatedStorage(ex.Message);

            }

        }

Isolated Storage space also let applications to read/write files without special permissions. The IsolatedStorageFileStream class provides methods to access files in the Isolated Storage and performs operations on them.

Save data in the Isolated Storage File
private void SaveLogToIsolatedStorage(string message)

        {

            using (IsolatedStorageFile isoStore = IsolatedStorageFile.GetUserStoreForApplication())

            {

                using (IsolatedStorageFileStream isoStream =

                    isoStore.OpenFile("Log.txt", FileMode.Append, FileAccess.Write))

                {

                    using (StreamWriter writer = new StreamWriter(isoStream))

                    {

                        writer.WriteLine(message);

                    }

                }

            }

        }

Read data from isolated Storage File
private void ButtonReadLog_Click(object sender, RoutedEventArgs e)

        {

            TextBoxResults.Text = ReadLogFromIsolatedStorage();           

        }
private string ReadLogFromIsolatedStorage()

        {

            string content = string.Empty;

            try

            {

                using (IsolatedStorageFile isoFile = IsolatedStorageFile.GetUserStoreForApplication())

                {

                    using (IsolatedStorageFileStream isoStream =

                        new IsolatedStorageFileStream("Log.txt", FileMode.Open, isoFile))

                    {

                        using (StreamReader sr = new StreamReader(isoStream))

                        {

                            content = sr.ReadToEnd();

                        }

                    }

                }

            }

            catch (IsolatedStorageException ex)

            {

                TextBoxResults.Text = ex.Message;

                return "";

            }

            return content;

        }

 

Further if you want any information to be globally available to all the users (Server-Side State Management) then one of the options is Application Resource. Anything added to the Application resource acts similar to Application State in ASP.NET (information will same throughout the application for all users).

Add object to the App Resource (in App.xaml.cs)
private void Application_Startup(object sender, StartupEventArgs e)

        {

            this.RootVisual = new Page();

            User user = new User();

            user.Name = "Nipun Tomar";

            user.Designation = "Project Lead";

            user.Address = "";

            user.City = "Philadelphia";

            App.Current.Resources.Add("UserInfo", user);

        }

Retrieve Information from App Resource (in Page.xaml.cs)
private void ButtonAppState_Click(object sender, RoutedEventArgs e)

        {

            try

            {

                User user = (User)App.Current.Resources["UserInfo"];

                TextBoxName.Text = user.Name;

                TextBoxDesignation.Text = user.Designation;

                TextBoxAddress.Text = user.Address;

                TextBoxCity.Text = user.City;

                TextBoxResults.Text = "User Details retrieved from Application Resources.";

                SaveLogToIsolatedStorage("User Details retrieved from Application Resources.");

            }

            catch (Exception ex)

            {

                TextBoxResults.Text = ex.Message;

                SaveLogToIsolatedStorage(ex.Message);

                ClearTextBoxes();

            }           

        }