/// <summary>
        /// Constructor for the Application object.
        /// </summary>
        public App()
        {
            // Global handler for uncaught exceptions.
            UnhandledException += Application_UnhandledException;

            // Standard Silverlight initialization
            InitializeComponent();

            // Phone-specific initialization
            InitializePhoneApplication();

            // Show graphics profiling information while debugging.
            if (System.Diagnostics.Debugger.IsAttached)
            {
                // Display the current frame rate counters
                Application.Current.Host.Settings.EnableFrameRateCounter = true;

                // Show the areas of the app that are being redrawn in each frame.
                //Application.Current.Host.Settings.EnableRedrawRegions = true;

                // Enable non-production analysis visualization mode,
                // which shows areas of a page that are handed off to GPU with a colored overlay.
                //Application.Current.Host.Settings.EnableCacheVisualization = true;

                // Disable the application idle detection by setting the UserIdleDetectionMode property of the
                // application's PhoneApplicationService object to Disabled.
                // Caution:- Use this under debug mode only. Application that disables user idle detection will continue to run
                // and consume battery power when the user is not using the phone.
                PhoneApplicationService.Current.UserIdleDetectionMode = IdleDetectionMode.Disabled;
            }

            // Specify the local database connection string.
            string DBConnectionString = "Data Source=isostore:/health.sdf";

            // Create the database if it does not exist.
            using (HealthTrackerDataContext db = new HealthTrackerDataContext(DBConnectionString))
            {
                if (db.DatabaseExists() == false)
                {
                    // Create the local database.
                    db.CreateDatabase();

                    // Prepopulate the categories.
                    db.categories.InsertOnSubmit(new Categories { ID = 1, Name = "口腔溃疡", DisplayName = "口腔溃疡", DescriptionIds = "", IsActivity = true, UpdateTime = DateTime.Now });
                    db.categories.InsertOnSubmit(new Categories { ID = 2, Name = "鼻血", DisplayName = "鼻血", DescriptionIds = "", IsActivity = true, UpdateTime = DateTime.Now });
                    db.categories.InsertOnSubmit(new Categories { ID = 3, Name = "痘痘", DisplayName = "痘痘", DescriptionIds = "", IsActivity = true, UpdateTime = DateTime.Now });
                    db.categories.InsertOnSubmit(new Categories { ID = 4, Name = "排便", DisplayName = "poop", DescriptionIds = "", IsActivity = true, UpdateTime = DateTime.Now });
                    db.categories.InsertOnSubmit(new Categories { ID = 5, Name = "早餐", DisplayName = "早餐", DescriptionIds = "", IsActivity = true, UpdateTime = DateTime.Now });
                    db.categories.InsertOnSubmit(new Categories { ID = 6, Name = "午餐", DisplayName = "午餐", DescriptionIds = "", IsActivity = true, UpdateTime = DateTime.Now });
                    db.categories.InsertOnSubmit(new Categories { ID = 7, Name = "晚餐", DisplayName = "晚餐", DescriptionIds = "", IsActivity = true, UpdateTime = DateTime.Now });

                    DateTime now = DateTime.Now;
                    DateTime current = new DateTime(now.Year, now.Month, now.Day);
                    DateTime yest = new DateTime(now.Year, now.Month, now.Day -1);

                    db.items.InsertOnSubmit(new Items { CategoryID = 1, StartTime = current, EndTime = DateTime.Now, IsActivity = true, UpdateTime = DateTime.Now });
                    db.items.InsertOnSubmit(new Items { CategoryID = 5, StartTime = yest, EndTime = yest, IsActivity = true, UpdateTime = DateTime.Now });

                    // Save categories to the database.
                    db.SubmitChanges();
                }
            }

            // Create the ViewModel object.
            viewModel = new MainViewModel(DBConnectionString);

            // Query the local database and load observable collections.
            viewModel.LoadCollectionsFromDatabase();
        }