How to: Persist and Restore Application-Scope Properties Across Application Sessions

This example shows how to persist application-scope properties when an application shuts down, and how to restore application-scope properties when an application is next launched.

Example

The application persists application-scope properties to, and restores them from, isolated storage. Isolated storage is a protected storage area that can safely be used by applications without file access permission. The App.xaml file defines the App_Startup method as the handler for the Application.Startup event, and the App_Exit method as the handler for the Application.Exit event, as shown in the highlighted lines of the first example. The second example shows a portion of the App.xaml.cs and App.xaml.vb files that highlights the code for the App_Startup method, which restores application-scope properties, and the App_Exit method, which saves application-scope properties.

<Application
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    x:Class="SDKSample.App"
    StartupUri="MainWindow.xaml" 
    Startup="App_Startup" 
    Exit="App_Exit">
    <Application.Resources>
        <SolidColorBrush x:Key="ApplicationScopeResource" Color="White"></SolidColorBrush>
    </Application.Resources>
</Application>

using System.Windows;
using System.IO;
using System.IO.IsolatedStorage;

namespace SDKSample
{
    public partial class App : Application
    {
        string filename = "App.txt";

        public App()
        {
            // Initialize application-scope property
            this.Properties["NumberOfAppSessions"] = 0;
        }

        private void App_Startup(object sender, StartupEventArgs e)
        {
            // Restore application-scope property from isolated storage
            IsolatedStorageFile storage = IsolatedStorageFile.GetUserStoreForDomain();
            try
            {
                using (IsolatedStorageFileStream stream = new IsolatedStorageFileStream(filename, FileMode.Open, storage))
                using (StreamReader reader = new StreamReader(stream))
                {
                    // Restore each application-scope property individually
                    while (!reader.EndOfStream)
                    {
                        string[] keyValue = reader.ReadLine().Split(new char[] {','});
                        this.Properties[keyValue[0]] = keyValue[1];
                    }
                }
            }
            catch (FileNotFoundException ex)
            {
                // Handle when file is not found in isolated storage:
                // * When the first application session
                // * When file has been deleted
            }
        }

        private void App_Exit(object sender, ExitEventArgs e)
        {
            // Persist application-scope property to isolated storage
            IsolatedStorageFile storage = IsolatedStorageFile.GetUserStoreForDomain();
            using (IsolatedStorageFileStream stream = new IsolatedStorageFileStream(filename, FileMode.Create, storage))
            using (StreamWriter writer = new StreamWriter(stream))
            {
                // Persist each application-scope property individually
                foreach (string key in this.Properties.Keys)
                {
                    writer.WriteLine("{0},{1}", key, this.Properties[key]);
                }
            }
        }
    }
}

Imports System.IO
Imports System.IO.IsolatedStorage

Namespace SDKSample
    Partial Public Class App
        Inherits Application
        Private filename As String = "App.txt"

        Public Sub New()
            ' Initialize application-scope property
            Me.Properties("NumberOfAppSessions") = 0
        End Sub

        Private Sub App_Startup(ByVal sender As Object, ByVal e As StartupEventArgs)
            ' Restore application-scope property from isolated storage
            Dim storage As IsolatedStorageFile = IsolatedStorageFile.GetUserStoreForDomain()
            Try
                Using stream As New IsolatedStorageFileStream(filename, FileMode.Open, storage)
                Using reader As New StreamReader(stream)
                    ' Restore each application-scope property individually
                    Do While Not reader.EndOfStream
                        Dim keyValue() As String = reader.ReadLine().Split(New Char() {","c})
                        Me.Properties(keyValue(0)) = keyValue(1)
                    Loop
                End Using
                End Using
            Catch ex As FileNotFoundException
                ' Handle when file is not found in isolated storage:
                ' * When the first application session
                ' * When file has been deleted
            End Try
        End Sub

        Private Sub App_Exit(ByVal sender As Object, ByVal e As ExitEventArgs)
            ' Persist application-scope property to isolated storage
            Dim storage As IsolatedStorageFile = IsolatedStorageFile.GetUserStoreForDomain()
            Using stream As New IsolatedStorageFileStream(filename, FileMode.Create, storage)
            Using writer As New StreamWriter(stream)
                ' Persist each application-scope property individually
                For Each key As String In Me.Properties.Keys
                    writer.WriteLine("{0},{1}", key, Me.Properties(key))
                Next key
            End Using
            End Using
        End Sub
    End Class
End Namespace