/// <summary>
/// Save the current <see cref="SessionState" />. Any <see cref="Frame" /> instances
/// registered with <see cref="RegisterFrame" /> will also preserve their current
/// navigation stack, which in turn gives their active <see cref="Page" /> an opportunity
/// to save its state.
/// </summary>
/// <returns>An asynchronous task that reflects when session state has been saved.</returns>
public static async Task SaveAsync()
{
try
{
// Notify Root Navigator and AuthenticationService that we are suspending
if (RootNavigatorLocator.IsAvailable)
{
EventFns.Forward(RootNavigatorLocator.GetPart(), new Suspending(SessionState));
}
if (AuthenticationServiceLocator.IsAvailable)
{
EventFns.Forward(AuthenticationServiceLocator.GetPart(), new Suspending(SessionState));
}
// Save the navigation state for all registered frames
foreach (var weakFrameReference in RegisteredFrames)
{
Frame frame;
if (weakFrameReference.TryGetTarget(out frame))
{
SaveFrameNavigationState(frame);
}
}
// Serialize the session state synchronously to avoid asynchronous access to shared
// state
var sessionData = new MemoryStream();
var serializer = new DataContractSerializer(typeof(Dictionary <string, object>), KnownTypes);
serializer.WriteObject(sessionData, _sessionState);
// Get an output stream for the SessionState file and write the state asynchronously
var file =
await
ApplicationData.Current.LocalFolder.CreateFileAsync(SessionStateFilename,
CreationCollisionOption.ReplaceExisting);
using (var fileStream = await file.OpenStreamForWriteAsync())
{
sessionData.Seek(0, SeekOrigin.Begin);
await sessionData.CopyToAsync(fileStream);
await fileStream.FlushAsync();
}
}
catch (Exception e)
{
throw new SuspensionManagerException(e);
}
}
/// <summary>
/// Restores previously saved <see cref="SessionState" />. Any <see cref="Frame" /> instances
/// registered with <see cref="RegisterFrame" /> will also restore their prior navigation
/// state, which in turn gives their active <see cref="Page" /> an opportunity restore its
/// state.
/// </summary>
/// <returns>
/// An asynchronous task that reflects when session state has been read. The
/// content of <see cref="SessionState" /> should not be relied upon until this task
/// completes.
/// </returns>
public static async Task RestoreAsync()
{
_sessionState = new Dictionary <String, Object>();
try
{
// Get the input stream for the SessionState file
var file = await ApplicationData.Current.LocalFolder.GetFileAsync(SessionStateFilename);
using (var inStream = await file.OpenSequentialReadAsync())
{
// Deserialize the Session State
var serializer = new DataContractSerializer(typeof(Dictionary <string, object>), KnownTypes);
_sessionState = (Dictionary <string, object>)serializer.ReadObject(inStream.AsStreamForRead());
}
// Notify Root Navigator and AuthenticationService that we are restoring
if (RootNavigatorLocator.IsAvailable)
{
EventFns.Forward(RootNavigatorLocator.GetPart(), new Restoring(SessionState));
}
if (AuthenticationServiceLocator.IsAvailable)
{
EventFns.Forward(AuthenticationServiceLocator.GetPart(), new Restoring(SessionState));
}
// Restore any registered frames to their saved state
foreach (var weakFrameReference in RegisteredFrames)
{
Frame frame;
if (weakFrameReference.TryGetTarget(out frame))
{
frame.ClearValue(FrameSessionStateProperty);
RestoreFrameNavigationState(frame);
}
}
}
catch (Exception e)
{
throw new SuspensionManagerException(e);
}
}
