/// <summary>
/// Used to save the navigation stack and should be called in the suspending event.
/// </summary>
public async Task SaveAsync()
{
if (StateManager != null)
{
ProcessSuspend();
string frameKey = string.IsNullOrEmpty(_frameKey) ? PageNavigator.DefaultFrameKey : _frameKey;
var frameDictionary = StateManager.GetDictionary(frameKey, true);
frameDictionary[PageNavigator.NavigationStackKey] = NavigationFrame.GetNavigationState();
await StateManager.SaveAsync();
}
}