public OrderViewModel()
        {
            Title   = "New order";
            Clients = DataStore.GetClientsAsync().Result.ToList();

            Items            = new ObservableCollection <Item>();
            LoadItemsCommand = new Command(async() => await ExecuteLoadItemsCommand());

            MessagingCenter.Subscribe <NewItemPage, Item>(this, "AddItem", async(obj, item) =>
            {
                var newItem = item as Item;
                Items.Add(newItem);
                await DataStore.AddItemAsync(newItem);
            });

            MessagingCenter.Subscribe <ItemsPage, Item>(this, "QuantityChanged", async(obj, item) =>
            {
                var newItem = item as Item;
                await DataStore.UpdateItemAsync(newItem);
                LoadItemsCommand.Execute(null);
            });

            MessagingCenter.Subscribe <ItemsPage, Item>(this, "DeleteItem", async(obj, item) =>
            {
                var newItem = item as Item;
                await DataStore.DeleteItemAsync(newItem.Id);
                LoadItemsCommand.Execute(null);
            });

            MessagingCenter.Subscribe <LogInPage, Distributor>(this, "LogIn", async(obj, dist) =>
            {
                var newDistibutor = dist as Distributor;
                await DataStore.AddDistributorAsync(newDistibutor);
                DataTransformer.SaveClientsToDB(DataRequester.MakeRequest(RequestTo.GetClients, newDistibutor.DistributorId.ToString()));
            });
        }